[release-branch.go1.18] go1.18.5

Change-Id: I4ca2e873fa21fb4676bc1d0e382bd8fd407a2986
Reviewed-on: https://go-review.googlesource.com/c/go/+/420555
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Gopher Robot <gobot@golang.org>
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

VERSION

@@ -0,0 +1 @@
+go1.18.5

codereview.cfg

@@ -1 +1,2 @@
-branch: master
+branch: release-branch.go1.18
+parent-branch: master

doc/go_spec.html

@@ -1,26 +1,16 @@
 <!--{
-	"Title": "The Go Programming Language Specification - Go 1.18 Draft",
-	"Subtitle": "Version of Feb 28, 2022",
+	"Title": "The Go Programming Language Specification",
+	"Subtitle": "Version of March 10, 2022",
 	"Path": "/ref/spec"
 }-->
 
-<h2>Earlier version</h2>
-
-<p>
-For the pre-Go1.18 specification without generics support see
-<a href="/doc/go1.17_spec.html">The Go Programming Language Specification</a>.
-</p>
-
-<!-- TODO(gri) remove this before the final release -->
-<p><b>
-[For reviewers: Sections where we know of missing prose are marked like this. The markers will be removed before the release.]
-</b></p>
-
 <h2 id="Introduction">Introduction</h2>
 
 <p>
-This is a reference manual for the Go programming language. For
-more information and other documents, see <a href="/">golang.org</a>.
+This is the reference manual for the Go programming language.
+The pre-Go1.18 version, without generics, can be found
+<a href="/doc/go1.17_spec.html">here</a>.
+For more information and other documents, see <a href="/">golang.org</a>.
 </p>
 
 <p>
@@ -766,7 +756,7 @@ type given in its declaration, the type provided in the
 <code>new</code> call or composite literal, or the type of
 an element of a structured variable.
 Variables of interface type also have a distinct <i>dynamic type</i>,
-which is the concrete type of the value assigned to the variable at run time
+which is the (non-interface) type of the value assigned to the variable at run time
 (unless the value is the predeclared identifier <code>nil</code>,
 which has no type).
 The dynamic type may vary during execution but values stored in interface
@@ -812,7 +802,7 @@ TypeLit   = ArrayType | StructType | PointerType | FunctionType | InterfaceType
 <p>
 The language <a href="#Predeclared_identifiers">predeclares</a> certain type names.
 Others are introduced with <a href="#Type_declarations">type declarations</a>
-or <a href="#Type_parameter_lists">type parameter lists</a>.
+or <a href="#Type_parameter_declarations">type parameter lists</a>.
 <i>Composite types</i>&mdash;array, struct, pointer, function,
 interface, slice, map, and channel types&mdash;may be constructed using
 type literals.
@@ -987,7 +977,7 @@ built-in function <a href="#Length_and_capacity"><code>cap(a)</code></a>.
 </p>
 
 <p>
-A new, initialized slice value for a given element type <code>T</code> is
+A new, initialized slice value for a given element type <code>T</code> may be
 made using the built-in function
 <a href="#Making_slices_maps_and_channels"><code>make</code></a>,
 which takes a slice type
@@ -1422,7 +1412,7 @@ interface {
 	~int
 }
 
-// An interface representing all types with underlying type int which implement the String method.
+// An interface representing all types with underlying type int that implement the String method.
 interface {
 	~int
 	String() string
@@ -1455,32 +1445,32 @@ Union elements denote unions of type sets:
 </p>
 
 <pre>
-// The Floats interface represents all floating-point types
+// The Float interface represents all floating-point types
 // (including any named types whose underlying types are
 // either float32 or float64).
-type Floats interface {
+type Float interface {
 	~float32 | ~float64
 }
 </pre>
 
 <p>
-In a union, a term cannot be a type parameter, and the type sets of all
+In a union, a term cannot be a <a href="#Type_parameter_declarations">type parameter</a>, and the type sets of all
 non-interface terms must be pairwise disjoint (the pairwise intersection of the type sets must be empty).
 Given a type parameter <code>P</code>:
 </p>
 
 <pre>
 interface {
-	P                 // illegal: the term P is a type parameter
-	int | P           // illegal: the term P is a type parameter
-	~int | MyInt      // illegal: the type sets for ~int and MyInt are not disjoint (~int includes MyInt)
-	float32 | Floats  // overlapping type sets but Floats is an interface
+	P                // illegal: P is a type parameter
+	int | P          // illegal: P is a type parameter
+	~int | MyInt     // illegal: the type sets for ~int and MyInt are not disjoint (~int includes MyInt)
+	float32 | Float  // overlapping type sets but Float is an interface
 }
 </pre>
 
 <p>
 Implementation restriction:
-A union with more than one term cannot contain the
+A union (with more than one term) cannot contain the
 <a href="#Predeclared_identifiers">predeclared identifier</a> <code>comparable</code>
 or interfaces that specify methods, or embed <code>comparable</code> or interfaces
 that specify methods.
@@ -1494,12 +1484,12 @@ non-interface types.
 </p>
 
 <pre>
-var x Floats                     // illegal: Floats is not a basic interface
+var x Float                     // illegal: Float is not a basic interface
 
-var x interface{} = Floats(nil)  // illegal
+var x interface{} = Float(nil)  // illegal
 
 type Floatish struct {
-	f Floats                 // illegal
+	f Float                 // illegal
 }
 </pre>
 
@@ -1545,7 +1535,7 @@ A type <code>T</code> implements an interface <code>I</code> if
 </ul>
 
 <p>
-A value <code>x</code> of type <code>T</code> implements an interface if <code>T</code>
+A value of type <code>T</code> implements an interface if <code>T</code>
 implements the interface.
 </p>
 
@@ -1701,10 +1691,9 @@ Each type <code>T</code> has an <i>underlying type</i>: If <code>T</code>
 is one of the predeclared boolean, numeric, or string types, or a type literal,
 the corresponding underlying type is <code>T</code> itself.
 Otherwise, <code>T</code>'s underlying type is the underlying type of the
-type to which <code>T</code> refers in its <a href="#Type_declarations">type
-declaration</a>. The underlying type of a type parameter is the
-underlying type of its <a href="#Type_constraints">type constraint</a>, which
-is always an interface.
+type to which <code>T</code> refers in its declaration.
+For a type parameter that is the underlying type of its
+<a href="#Type_constraints">type constraint</a>, which is always an interface.
 </p>
 
 <pre>
@@ -1755,7 +1744,7 @@ direction.
 </ol>
 
 <p>
-All other interfaces don't have a core type.
+No other interfaces have a core type.
 </p>
 
 <p>
@@ -1775,7 +1764,7 @@ depending on the direction of the directional channels present.
 
 <p>
 By definition, a core type is never a <a href="#Type_definitions">defined type</a>,
-<a href="#Type_parameter_lists">type parameter</a>, or
+<a href="#Type_parameter_declarations">type parameter</a>, or
 <a href="#Interface_types">interface type</a>.
 </p>
 
@@ -1795,7 +1784,7 @@ interface{ ~[]*data; String() string }    // []*data
 </pre>
 
 <p>
-Examples of interfaces whithout core types:
+Examples of interfaces without core types:
 </p>
 
 <pre>
@@ -1805,70 +1794,6 @@ interface{ chan int | chan&lt;- string }     // channels have different element
 interface{ &lt;-chan int | chan&lt;- int }      // directional channels have different directions
 </pre>
 
-<h3 id="Specific_types">Specific types</h3>
-
-<p><b>
-[The definition of specific types is not quite correct yet.]
-</b></p>
-
-<p>
-An interface specification that contains <a href="#Interface_types">type elements</a>
-defines a (possibly empty) set of <i>specific types</i>.
-Loosely speaking, these are the types <code>T</code> that appear in the
-interface definition in terms of the form <code>T</code>, <code>~T</code>,
-or in unions of such terms.
-</p>
-
-<p>
-More precisely, for a given interface, the set of specific types corresponds to
-the set 𝑅 of representative types of the interface, if 𝑅 is non-empty and finite.
-Otherwise, if 𝑅 is empty or infinite, the interface has <i>no specific types</i>.
-</p>
-
-<p>
-For a given interface, type element or type term, the set 𝑅 of representative types is defined as follows:
-</p>
-
-<ul>
-	<li>For an interface with no type elements, 𝑅 is the (infinite) set of all types.
-	</li>
-
-	<li>For an interface with type elements,
-		𝑅 is the intersection of the representative types of its type elements.
-	</li>
-
-	<li>For a non-interface type term <code>T</code> or a term of the form <code>~T</code>,
-		𝑅 is the set consisting of the type <code>T</code>.
-	</li>
-
-	<li>For a <i>union</i> of terms
-		<code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>,
-		𝑅 is the union of the representative types of the terms.
-	</li>
-</ul>
-
-<p>
-An interface may have specific types even if its <a href="#Interface_types">type set</a>
-is empty.
-</p>
-
-<p>
-Examples of interfaces with their specific types:
-</p>
-
-<pre>
-interface{}                    // no specific types
-interface{ int }               // int
-interface{ ~string }           // string
-interface{ int|~string }       // int, string
-interface{ Celsius|Kelvin }    // Celsius, Kelvin
-interface{ float64|any }       // no specific types (union is all types)
-interface{ int; m() }          // int (but type set is empty because int has no method m)
-interface{ ~int; m() }         // int (but type set is infinite because many integer types have a method m)
-interface{ int; any }          // int
-interface{ int; string }       // no specific types (intersection is empty)
-</pre>
-
 <h3 id="Type_identity">Type identity</h3>
 
 <p>
@@ -1973,21 +1898,21 @@ defined type while the latter is a type literal
 <h3 id="Assignability">Assignability</h3>
 
 <p>
-A value <code>x</code> is <i>assignable</i> to a <a href="#Variables">variable</a> of type <code>T</code>
+A value <code>x</code> of type <code>V</code> is <i>assignable</i> to a <a href="#Variables">variable</a> of type <code>T</code>
 ("<code>x</code> is assignable to <code>T</code>") if one of the following conditions applies:
 </p>
 
 <ul>
 <li>
-<code>x</code>'s type is identical to <code>T</code>.
+<code>V</code> and <code>T</code> are identical.
 </li>
 <li>
-<code>x</code>'s type <code>V</code> and <code>T</code> have identical
+<code>V</code> and <code>T</code> have identical
 <a href="#Underlying_types">underlying types</a> and at least one of <code>V</code>
 or <code>T</code> is not a <a href="#Types">named type</a>.
 </li>
 <li>
-<code>x</code>'s type <code>V</code> and <code>T</code> are channel types with
+<code>V</code> and <code>T</code> are channel types with
 identical element types, <code>V</code> is a bidirectional channel,
 and at least one of <code>V</code> or <code>T</code> is not a <a href="#Types">named type</a>.
 </li>
@@ -2008,25 +1933,24 @@ by a value of type <code>T</code>.
 </ul>
 
 <p>
-Additionally, if <code>x</code>'s type <code>V</code> or <code>T</code> are type parameters
-with <a href="#Specific_types">specific types</a>, <code>x</code>
+Additionally, if <code>x</code>'s type <code>V</code> or <code>T</code> are type parameters, <code>x</code>
 is assignable to a variable of type <code>T</code> if one of the following conditions applies:
 </p>
 
 <ul>
 <li>
 <code>x</code> is the predeclared identifier <code>nil</code>, <code>T</code> is
-a type parameter, and <code>x</code> is assignable to each specific type of
-<code>T</code>.
+a type parameter, and <code>x</code> is assignable to each type in
+<code>T</code>'s type set.
 </li>
 <li>
 <code>V</code> is not a <a href="#Types">named type</a>, <code>T</code> is
-a type parameter, and <code>x</code> is assignable to each specific type of
-<code>T</code>.
+a type parameter, and <code>x</code> is assignable to each type in
+<code>T</code>'s type set.
 </li>
 <li>
 <code>V</code> is a type parameter and <code>T</code> is not a named type,
-and values of each specific type of <code>V</code> are assignable
+and values of each type in <code>V</code>'s type set are assignable
 to <code>T</code>.
 </li>
 </ul>
@@ -2036,7 +1960,7 @@ to <code>T</code>.
 <p>
 A <a href="#Constants">constant</a> <code>x</code> is <i>representable</i>
 by a value of type <code>T</code>,
-where <code>T</code> is not a <a href="#Type_parameter_lists">type parameter</a>,
+where <code>T</code> is not a <a href="#Type_parameter_declarations">type parameter</a>,
 if one of the following conditions applies:
 </p>
 
@@ -2061,9 +1985,9 @@ are representable by values of <code>T</code>'s component type (<code>float32</c
 </ul>
 
 <p>
-If <code>T</code> is a type parameter with <a href="#Specific_types">specific types</a>,
+If <code>T</code> is a type parameter,
 <code>x</code> is representable by a value of type <code>T</code> if <code>x</code> is representable
-by a value of each specific type of <code>T</code>.
+by a value of each type in <code>T</code>'s type set.
 </p>
 
 <pre>
@@ -2176,6 +2100,7 @@ Blocks nest and influence <a href="#Declarations_and_scope">scoping</a>.
 A <i>declaration</i> binds a non-<a href="#Blank_identifier">blank</a> identifier to a
 <a href="#Constant_declarations">constant</a>,
 <a href="#Type_declarations">type</a>,
+<a href="#Type_parameter_declarations">type parameter</a>,
 <a href="#Variable_declarations">variable</a>,
 <a href="#Function_declarations">function</a>,
 <a href="#Labeled_statements">label</a>, or
@@ -2220,13 +2145,13 @@ Go is lexically scoped using <a href="#Blocks">blocks</a>:
 	<li>The scope of an identifier denoting a method receiver, function parameter,
 	    or result variable is the function body.</li>
 
-	<li>The scope of an identifier denoting a type parameter of a generic function
+	<li>The scope of an identifier denoting a type parameter of a function
 	    or declared by a method receiver is the function body and all parameter lists of the
 	    function.
 	</li>
 
-	<li>The scope of an identifier denoting a type parameter of a generic type
-	    begins after the name of the generic type and ends at the end
+	<li>The scope of an identifier denoting a type parameter of a type
+	    begins after the name of the type and ends at the end
 	    of the TypeSpec.</li>
 
 	<li>The scope of a constant or variable identifier declared
@@ -2512,7 +2437,7 @@ type (
 
 type TreeNode struct {
 	left, right *TreeNode
-	value *Comparable
+	value any
 }
 
 type Block interface {
@@ -2573,7 +2498,7 @@ func (tz TimeZone) String() string {
 </pre>
 
 <p>
-If the type definition specifies <a href="#Type_parameter_lists">type parameters</a>,
+If the type definition specifies <a href="#Type_parameter_declarations">type parameters</a>,
 the type name denotes a <i>generic type</i>.
 Generic types must be <a href="#Instantiations">instantiated</a> when they
 are used.
@@ -2584,15 +2509,10 @@ type List[T any] struct {
 	next  *List[T]
 	value T
 }
-
-type Tree[T constraints.Ordered] struct {
-	left, right *Tree[T]
-	value       T
-}
 </pre>
 
 <p>
-The given type cannot be a type parameter in a type definition.
+In a type definition the given type cannot be a type parameter.
 </p>
 
 <pre>
@@ -2604,8 +2524,8 @@ func f[T any]() {
 </pre>
 
 <p>
-A generic type may also have methods associated with it. In this case,
-the method receivers must declare the same number of type parameters as
+A generic type may also have <a href="#Method_declarations">methods</a> associated with it.
+In this case, the method receivers must declare the same number of type parameters as
 present in the generic type definition.
 </p>
 
@@ -2614,7 +2534,7 @@ present in the generic type definition.
 func (l *List[T]) Len() int  { … }
 </pre>
 
-<h3 id="Type_parameter_lists">Type parameter lists</h3>
+<h3 id="Type_parameter_declarations">Type parameter declarations</h3>
 
 <p>
 A type parameter list declares the <i>type parameters</i> of a generic function or type declaration.
@@ -2653,22 +2573,22 @@ has a corresponding (meta-)type which is called its
 
 <p>
 A parsing ambiguity arises when the type parameter list for a generic type
-declares a single type parameter with a type constraint of the form <code>*C</code>
-or <code>(C)</code> where <code>C</code> is not a (possibly parenthesized)
-<a href="#Types">type literal</a>:
+declares a single type parameter <code>P</code> with a constraint <code>C</code>
+such that the text <code>P C</code> forms a valid expression:
 </p>
 
 <pre>
 type T[P *C] …
 type T[P (C)] …
+type T[P *C|Q] …
+…
 </pre>
 
 <p>
-In these rare cases, the type parameter declaration is indistinguishable from
-the expressions <code>P*C</code> or <code>P(C)</code> and the type declaration
-is parsed as an array type declaration.
-To resolve the ambiguity, embed the constraint in an interface or use a trailing
-comma:
+In these rare cases, the type parameter list is indistinguishable from an
+expression and the type declaration is parsed as an array type declaration.
+To resolve the ambiguity, embed the constraint in an
+<a href="#Interface_types">interface</a> or use a trailing comma:
 </p>
 
 <pre>
@@ -2682,6 +2602,11 @@ of a <a href="#Method_declarations">method declaration</a> associated
 with a generic type.
 </p>
 
+<!--
+This section needs to explain if and what kind of cycles are permitted
+using type parameters in a type parameter list.
+-->
+
 <h4 id="Type_constraints">Type constraints</h4>
 
 <p>
@@ -2701,10 +2626,10 @@ the enclosing <code>interface{ … }</code> may be omitted for convenience:
 </p>
 
 <pre>
-[T *P]                             // = [T interface{*P}]
-[T ~int]                           // = [T interface{~int}]
-[T int|string]                     // = [T interface{int|string}]
-type Constraint ~int               // illegal: ~int is not inside a type parameter list
+[T []P]                      // = [T interface{[]P}]
+[T ~int]                     // = [T interface{~int}]
+[T int|string]               // = [T interface{int|string}]
+type Constraint ~int         // illegal: ~int is not inside a type parameter list
 </pre>
 
 <!--
@@ -2716,7 +2641,7 @@ other interfaces based on their type sets. But this should get us going for now.
 <p>
 The <a href="#Predeclared_identifiers">predeclared</a>
 <a href="#Interface_types">interface type</a> <code>comparable</code>
-denotes the set of all concrete (non-interface) types that are
+denotes the set of all non-interface types that are
 <a href="#Comparison_operators">comparable</a>. Specifically,
 a type <code>T</code> implements <code>comparable</code> if:
 </p>
@@ -2897,14 +2822,14 @@ func IndexRune(s string, r rune) int {
 </pre>
 
 <p>
-If the function declaration specifies <a href="#Type_parameter_lists">type parameters</a>,
+If the function declaration specifies <a href="#Type_parameter_declarations">type parameters</a>,
 the function name denotes a <i>generic function</i>.
-Generic functions must be <a href="#Instantiations">instantiated</a> when they
-are used.
+A generic function must be <a href="#Instantiations">instantiated</a> before it can be
+called or used as a value.
 </p>
 
 <pre>
-func min[T constraints.Ordered](x, y T) T {
+func min[T ~int|~float64](x, y T) T {
 	if x &lt; y {
 		return x
 	}
@@ -2963,7 +2888,7 @@ the non-blank method and field names must be distinct.
 </p>
 
 <p>
-Given defined type <code>Point</code>, the declarations
+Given defined type <code>Point</code> the declarations
 </p>
 
 <pre>
@@ -2987,13 +2912,10 @@ to the base type <code>Point</code>.
 If the receiver base type is a <a href="#Type_declarations">generic type</a>, the
 receiver specification must declare corresponding type parameters for the method
 to use. This makes the receiver type parameters available to the method.
-</p>
-
-<p>
 Syntactically, this type parameter declaration looks like an
-<a href="#Instantiations">instantiation</a> of the receiver base type, except that
-the type arguments are the type parameters being declared, one for each type parameter
-of the receiver base type.
+<a href="#Instantiations">instantiation</a> of the receiver base type: the type
+arguments must be identifiers denoting the type parameters being declared, one
+for each type parameter of the receiver base type.
 The type parameter names do not need to match their corresponding parameter names in the
 receiver base type definition, and all non-blank parameter names must be unique in the
 receiver parameter section and the method signature.
@@ -3007,8 +2929,8 @@ type Pair[A, B any] struct {
 	b B
 }
 
-func (p Pair[A, B]) Swap() Pair[B, A]  { return Pair[B, A]{p.b, p.a} }
-func (p Pair[First, _]) First() First  { return p.a }
+func (p Pair[A, B]) Swap() Pair[B, A]  { … }  // receiver declares A, B
+func (p Pair[First, _]) First() First  { … }  // receiver declares First, corresponds to A in Pair
 </pre>
 
 <h2 id="Expressions">Expressions</h2>
@@ -3048,6 +2970,14 @@ The <a href="#Blank_identifier">blank identifier</a> may appear as an
 operand only on the left-hand side of an <a href="#Assignments">assignment</a>.
 </p>
 
+<p>
+Implementation restriction: A compiler need not report an error if an operand's
+type is a <a href="#Type_parameter_declarations">type parameter</a> with an empty
+<a href="#Interface_types">type set</a>. Functions with such type parameters
+cannot be <a href="#Instantiations">instantiated</a>; any attempt will lead
+to an error at the instantiation site.
+</p>
+
 <h3 id="Qualified_identifiers">Qualified identifiers</h3>
 
 <p>
@@ -3354,10 +3284,6 @@ f.p[i].x()
 
 <h3 id="Selectors">Selectors</h3>
 
-<p><b>
-[This section is missing rules for x.f where x's type is a type parameter and f is a field.]
-</b></p>
-
 <p>
 For a <a href="#Primary_expressions">primary expression</a> <code>x</code>
 that is not a <a href="#Package_clause">package name</a>, the
@@ -3758,7 +3684,7 @@ The following rules apply:
 </p>
 
 <p>
-If <code>a</code> is not a map:
+If <code>a</code> is neither a map nor a type parameter:
 </p>
 <ul>
 	<li>the index <code>x</code> must be an untyped constant or its
@@ -3827,23 +3753,22 @@ For <code>a</code> of <a href="#Map_types">map type</a> <code>M</code>:
 </ul>
 
 <p>
-For <code>a</code> of <a href="#Type_parameter_lists">type parameter type</a> <code>P</code>:
+For <code>a</code> of <a href="#Type_parameter_declarations">type parameter type</a> <code>P</code>:
 </p>
 <ul>
-	<li><code>P</code> must have <a href="#Specific_types">specific types</a>.</li>
 	<li>The index expression <code>a[x]</code> must be valid for values
-	    of all specific types of <code>P</code>.</li>
-	<li>The element types of all specific types of <code>P</code> must be identical.
+	    of all types in <code>P</code>'s type set.</li>
+	<li>The element types of all types in <code>P</code>'s type set must be identical.
 	    In this context, the element type of a string type is <code>byte</code>.</li>
-	<li>If there is a map type among the specific types of <code>P</code>,
-	    all specific types must be map types, and the respective key types
+	<li>If there is a map type in the type set of <code>P</code>,
+	    all types in that type set must be map types, and the respective key types
 	    must be all identical.</li>
 	<li><code>a[x]</code> is the array, slice, or string element at index <code>x</code>,
 	    or the map element with key <code>x</code> of the type argument
 	    that <code>P</code> is instantiated with, and the type of <code>a[x]</code> is
 	    the type of the (identical) element types.</li>
-	<li><code>a[x]</code> may not be assigned to if the specific types of <code>P</code>
-	    include string types.
+	<li><code>a[x]</code> may not be assigned to if <code>P</code>'s type set
+	    includes string types.
 </ul>
 
 <p>
@@ -4021,7 +3946,7 @@ If the indices are out of range at run time, a <a href="#Run_time_panics">run-ti
 
 <p>
 For an expression <code>x</code> of <a href="#Interface_types">interface type</a>,
-but not a <a href="#Type_parameter_lists">type parameter</a>, and a type <code>T</code>,
+but not a <a href="#Type_parameter_declarations">type parameter</a>, and a type <code>T</code>,
 the primary expression
 </p>
 
@@ -4236,7 +4161,7 @@ with the same underlying array.
 <p>
 A generic function or type is <i>instantiated</i> by substituting <i>type arguments</i>
 for the type parameters.
-Instantiation proceeds in two phases:
+Instantiation proceeds in two steps:
 </p>
 
 <ol>
@@ -4249,7 +4174,7 @@ including the type parameter list itself and any types in that list.
 
 <li>
 After substitution, each type argument must <a href="#Interface_types">implement</a>
-the <a href="#Type_parameter_lists">constraint</a> (instantiated, if necessary)
+the <a href="#Type_parameter_declarations">constraint</a> (instantiated, if necessary)
 of the corresponding type parameter. Otherwise instantiation fails.
 </li>
 </ol>
@@ -4262,55 +4187,57 @@ instantiating a function produces a new non-generic function.
 <pre>
 type parameter list    type arguments    after substitution
 
-[P any]                int               [int any]
-[S ~[]E, E any]        []int, int        [[]int ~[]int, int any]
-[P io.Writer]          string            [string io.Writer]         // illegal: string doesn't implement io.Writer
+[P any]                int               int implements any
+[S ~[]E, E any]        []int, int        []int implements ~[]int, int implements any
+[P io.Writer]          string            illegal: string doesn't implement io.Writer
 </pre>
 
 <p>
-Type arguments may be provided explicitly, or they may be partially or completely
-<a href="#Type_inference">inferred</a>.
-A partially provided type argument list cannot be empty; there must be at least the
-first argument.
-</p>
-
-<pre>
-type T[P1 ~int, P2 ~[]P1] struct{ … }
-
-T[]            // illegal: at least the first type argument must be present, even if it could be inferred
-T[int]         // argument for P1 explicitly provided, argument for P2 inferred
-T[int, []int]  // both arguments explicitly provided
-</pre>
-
-<p>
-A partial type argument list specifies a prefix of the full list of type arguments, leaving
-the remaining arguments to be inferred. Loosely speaking, type arguments may be omitted from
-"right to left".
-</p>
-
-<p>
-Generic types, and generic functions that are not <a href="#Calls">called</a>,
-require a type argument list for instantiation; if the list is partial, all
+For a generic function, type arguments may be provided explicitly, or they
+may be partially or completely <a href="#Type_inference">inferred</a>.
+A generic function that is is <i>not</i> <a href="#Calls">called</a> requires a
+type argument list for instantiation; if the list is partial, all
 remaining type arguments must be inferrable.
-Calls to generic functions may provide a (possibly partial) type
+A generic function that is called may provide a (possibly partial) type
 argument list, or may omit it entirely if the omitted type arguments are
 inferrable from the ordinary (non-type) function arguments.
 </p>
 
 <pre>
-func min[T constraints.Ordered](x, y T) T { … }
+func min[T ~int|~float64](x, y T) T { … }
 
-f := min                   // illegal: min must be instantiated when used without being called
+f := min                   // illegal: min must be instantiated with type arguments when used without being called
 minInt := min[int]         // minInt has type func(x, y int) int
 a := minInt(2, 3)          // a has value 2 of type int
 b := min[float64](2.0, 3)  // b has value 2.0 of type float64
 c := min(b, -1)            // c has value -1.0 of type float64
 </pre>
 
+<p>
+A partial type argument list cannot be empty; at least the first argument must be present.
+The list is a prefix of the full list of type arguments, leaving the remaining arguments
+to be inferred. Loosely speaking, type arguments may be omitted from "right to left".
+</p>
+
+<pre>
+func apply[S ~[]E, E any](s S, f(E) E) S { … }
+
+f0 := apply[]                  // illegal: type argument list cannot be empty
+f1 := apply[[]int]             // type argument for S explicitly provided, type argument for E inferred
+f2 := apply[[]string, string]  // both type arguments explicitly provided
+
+var bytes []byte
+r := apply(bytes, func(byte) byte { … })  // both type arguments inferred from the function arguments
+</pre>
+
+<p>
+For a generic type, all type arguments must always be provided explicitly.
+</p>
+
 <h3 id="Type_inference">Type inference</h3>
 
 <p>
-Missing type arguments may be <i>inferred</i> by a series of steps, described below.
+Missing function type arguments may be <i>inferred</i> by a series of steps, described below.
 Each step attempts to use known information to infer additional type arguments.
 Type inference stops as soon as all type arguments are known.
 After type inference is complete, it is still necessary to substitute all type arguments
@@ -4326,7 +4253,7 @@ Type inference is based on
 
 <ul>
 <li>
-	a <a href="#Type_parameter_lists">type parameter list</a>
+	a <a href="#Type_parameter_declarations">type parameter list</a>
 </li>
 <li>
 	a substitution map <i>M</i> initialized with the known type arguments, if any
@@ -4491,9 +4418,8 @@ unresolved type parameters left.
 </p>
 
 <p>
-Function argument type inference can be used when the function has ordinary parameters
-whose types are defined using the function's type parameters. Inference happens in two
-separate phases; each phase operates on a specific list of (parameter, argument) pairs:
+Inference happens in two separate phases; each phase operates on a specific list of
+(parameter, argument) pairs:
 </p>
 
 <ol>
@@ -4550,7 +4476,7 @@ Example:
 </p>
 
 <pre>
-func min[T constraints.Ordered](x, y T) T
+func min[T ~int|~float64](x, y T) T
 
 var x int
 min(x, 2.0)    // T is int, inferred from typed argument x; 2.0 is assignable to int
@@ -4841,9 +4767,8 @@ The bitwise logical and shift operators apply to integers only.
 </pre>
 
 <p>
-Excluding shifts, if the operand type is a <a href="#Type_parameter_lists">type parameter</a>,
-it must have <a href="#Specific_types">specific types</a>, and the operator must
-apply to each specific type.
+If the operand type is a <a href="#Type_parameter_declarations">type parameter</a>,
+the operator must apply to each type in that type set.
 The operands are represented as values of the type argument that the type parameter
 is <a href="#Instantiations">instantiated</a> with, and the operation is computed
 with the precision of that type argument. For example, given the function:
@@ -4866,11 +4791,6 @@ are computed with <code>float32</code> or <code>float64</code> precision,
 respectively, depending on the type argument for <code>F</code>.
 </p>
 
-<p>
-For shifts, the <a href="#Core_types">core type</a> of both operands must be
-an integer.
-</p>
-
 <h4 id="Integer_operators">Integer operators</h4>
 
 <p>
@@ -5296,7 +5216,7 @@ as for non-constant <code>x</code>.
 </p>
 
 <p>
-Converting a constant to a type that is not a <a href="#Type_parameter_lists">type parameter</a>
+Converting a constant to a type that is not a <a href="#Type_parameter_declarations">type parameter</a>
 yields a typed constant.
 </p>
 
@@ -5351,7 +5271,7 @@ in any of these cases:
 	<li>
 	ignoring struct tags (see below),
 	<code>x</code>'s type and <code>T</code> are not
-	<a href="#Type_parameter_lists">type parameters</a> but have
+	<a href="#Type_parameter_declarations">type parameters</a> but have
 	<a href="#Type_identity">identical</a> <a href="#Types">underlying types</a>.
 	</li>
 	<li>
@@ -5383,23 +5303,23 @@ in any of these cases:
 
 <p>
 Additionally, if <code>T</code> or <code>x</code>'s type <code>V</code> are type
-parameters with <a href="#Specific_types">specific types</a>, <code>x</code>
+parameters, <code>x</code>
 can also be converted to type <code>T</code> if one of the following conditions applies:
 </p>
 
 <ul>
 <li>
 Both <code>V</code> and <code>T</code> are type parameters and a value of each
-specific type of <code>V</code> can be converted to each specific type
-of <code>T</code>.
+type in <code>V</code>'s type set can be converted to each type in <code>T</code>'s
+type set.
 </li>
 <li>
 Only <code>V</code> is a type parameter and a value of each
-specific type of <code>V</code> can be converted to <code>T</code>.
+type in <code>V</code>'s type set can be converted to <code>T</code>.
 </li>
 <li>
 Only <code>T</code> is a type parameter and <code>x</code> can be converted to each
-specific type of <code>T</code>.
+type in <code>T</code>'s type set.
 </li>
 </ul>
 
@@ -6270,7 +6190,7 @@ switch x.(type) {
 Cases then match actual types <code>T</code> against the dynamic type of the
 expression <code>x</code>. As with type assertions, <code>x</code> must be of
 <a href="#Interface_types">interface type</a>, but not a
-<a href="#Type_parameter_lists">type parameter</a>, and each non-interface type
+<a href="#Type_parameter_declarations">type parameter</a>, and each non-interface type
 <code>T</code> listed in a case must implement the type of <code>x</code>.
 The types listed in the cases of a type switch must all be
 <a href="#Type_identity">different</a>.
@@ -6352,7 +6272,7 @@ if v == nil {
 </pre>
 
 <p>
-A <a href="#Type_parameter_lists">type parameter</a> or a <a href="#Type_declarations">generic type</a>
+A <a href="#Type_parameter_declarations">type parameter</a> or a <a href="#Type_declarations">generic type</a>
 may be used as a type in a case. If upon <a href="#Instantiations">instantiation</a> that type turns
 out to duplicate another entry in the switch, the first matching case is chosen.
 </p>
@@ -7093,10 +7013,9 @@ cap(s)    [n]T, *[n]T      array length (== n)
 </pre>
 
 <p>
-If the argument type is a <a href="#Type_parameter_lists">type parameter</a> <code>P</code>,
-<code>P</code> must have <a href="#Specific_types">specific types</a>, and
+If the argument type is a <a href="#Type_parameter_declarations">type parameter</a> <code>P</code>,
 the call <code>len(e)</code> (or <code>cap(e)</code> respectively) must be valid for
-each specific type of <code>P</code>.
+each type in <code>P</code>'s type set.
 The result is the length (or capacity, respectively) of the argument whose type
 corresponds to the type argument with which <code>P</code> was
 <a href="#Instantiations">instantiated</a>.
@@ -7197,8 +7116,9 @@ make(T, n)       channel      buffered channel of type T, buffer size n
 
 
 <p>
-Each of the size arguments <code>n</code> and <code>m</code> must be of <a href="#Numeric_types">integer type</a>
-or an untyped <a href="#Constants">constant</a>.
+Each of the size arguments <code>n</code> and <code>m</code> must be of <a href="#Numeric_types">integer type</a>,
+have a <a href="#Interface_types">type set</a> containing only integer types,
+or be an untyped <a href="#Constants">constant</a>.
 A constant size argument must be non-negative and <a href="#Representability">representable</a>
 by a value of type <code>int</code>; if it is an untyped constant it is given type <code>int</code>.
 If both <code>n</code> and <code>m</code> are provided and are constant, then
@@ -7235,9 +7155,9 @@ by the arguments overlaps.
 <p>
 The <a href="#Function_types">variadic</a> function <code>append</code>
 appends zero or more values <code>x</code> to a slice <code>s</code>
-and returns the resulting slice.
+and returns the resulting slice of the same type as <code>s</code>.
 The <a href="#Core_types">core type</a> of <code>s</code> must be a slice
-of the form <code>[]E</code>.
+of type <code>[]E</code>.
 The values <code>x</code> are passed to a parameter of type <code>...E</code>
 and the respective <a href="#Passing_arguments_to_..._parameters">parameter
 passing rules</a> apply.
@@ -7247,7 +7167,7 @@ followed by <code>...</code>. This form appends the bytes of the string.
 </p>
 
 <pre class="grammar">
-append(s S, x ...E) S  // E is the element type of the core type of S
+append(s S, x ...E) S  // core type of S is []E
 </pre>
 
 <p>
@@ -7317,9 +7237,8 @@ delete(m, k)  // remove element m[k] from map m
 </pre>
 
 <p>
-If the type of <code>m</code> is a <a href="#Type_parameter_lists">type parameter</a>,
-it must have <a href="#Specific_types">specific types</a>, all specific types
-must be maps, and they must all have identical key types.
+If the type of <code>m</code> is a <a href="#Type_parameter_declarations">type parameter</a>,
+all types in that type set must be maps, and they must all have identical key types.
 </p>
 
 <p>
@@ -7330,10 +7249,6 @@ does not exist, <code>delete</code> is a no-op.
 
 <h3 id="Complex_numbers">Manipulating complex numbers</h3>
 
-<p><b>
-[We don't support generic arguments for these built-ins for Go 1.18.]
-</b></p>
-
 <p>
 Three functions assemble and disassemble complex numbers.
 The built-in function <code>complex</code> constructs a complex
@@ -7396,6 +7311,10 @@ const c = imag(b)                  // untyped constant -1.4
 _ = imag(3 &lt;&lt; s)                   // illegal: 3 assumes complex type, cannot shift
 </pre>
 
+<p>
+Arguments of type parameter type are not permitted.
+</p>
+
 <h3 id="Handling_panics">Handling panics</h3>
 
 <p> Two built-in functions, <code>panic</code> and <code>recover</code>,
@@ -8004,11 +7923,17 @@ func Add(ptr Pointer, len IntegerType) Pointer
 func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType
 </pre>
 
+<!--
+These conversions also apply to type parameters with suitable core types.
+Determine if we can simply use core type insted of underlying type here,
+of if the general conversion rules take care of this.
+-->
+
 <p>
 A <code>Pointer</code> is a <a href="#Pointer_types">pointer type</a> but a <code>Pointer</code>
 value may not be <a href="#Address_operators">dereferenced</a>.
-Any pointer or value of <a href="#Types">underlying type</a> <code>uintptr</code> can be converted to
-a type of underlying type <code>Pointer</code> and vice versa.
+Any pointer or value of <a href="#Types">underlying type</a> <code>uintptr</code> can be
+<a href="#Conversions">converted</a> to a type of underlying type <code>Pointer</code> and vice versa.
 The effect of converting between <code>Pointer</code> and <code>uintptr</code> is implementation-defined.
 </p>
 
@@ -8055,7 +7980,8 @@ uintptr(unsafe.Pointer(&amp;x)) % unsafe.Alignof(x) == 0
 
 <p>
 A (variable of) type <code>T</code> has <i>variable size</i> if <code>T</code>
-is a type parameter, or if it is an array or struct type containing elements
+is a <a href="#Type_parameter_declarations">type parameter</a>, or if it is an
+array or struct type containing elements
 or fields of variable size. Otherwise the size is <i>constant</i>.
 Calls to <code>Alignof</code>, <code>Offsetof</code>, and <code>Sizeof</code>
 are compile-time <a href="#Constant_expressions">constant expressions</a> of

misc/cgo/testplugin/plugin_test.go

@@ -283,6 +283,12 @@ func TestMethod2(t *testing.T) {
 	run(t, "./method2.exe")
 }
 
+func TestMethod3(t *testing.T) {
+	goCmd(t, "build", "-buildmode=plugin", "-o", "method3.so", "./method3/plugin.go")
+	goCmd(t, "build", "-o", "method3.exe", "./method3/main.go")
+	run(t, "./method3.exe")
+}
+
 func TestIssue44956(t *testing.T) {
 	goCmd(t, "build", "-buildmode=plugin", "-o", "issue44956p1.so", "./issue44956/plugin1.go")
 	goCmd(t, "build", "-buildmode=plugin", "-o", "issue44956p2.so", "./issue44956/plugin2.go")

misc/cgo/testplugin/testdata/method3/main.go

@@ -0,0 +1,32 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// An unexported method can be reachable from the plugin via interface
+// when a package is shared. So it need to be live.
+
+package main
+
+import (
+	"plugin"
+
+	"testplugin/method3/p"
+)
+
+var i p.I
+
+func main() {
+	pl, err := plugin.Open("method3.so")
+	if err != nil {
+		panic(err)
+	}
+
+	f, err := pl.Lookup("F")
+	if err != nil {
+		panic(err)
+	}
+
+	f.(func())()
+
+	i = p.T(123)
+}

misc/cgo/testplugin/testdata/method3/p/p.go

@@ -0,0 +1,17 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type T int
+
+func (T) m() { println("m") }
+
+type I interface { m() }
+
+func F() {
+	i.m()
+}
+
+var i I = T(123)

misc/cgo/testplugin/testdata/method3/plugin.go

@@ -0,0 +1,11 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "testplugin/method3/p"
+
+func main() {}
+
+func F() { p.F() }

misc/cgo/testsanitizers/testdata/tsan11.go

@@ -45,7 +45,7 @@ static void register_handler(int signo) {
 import "C"
 
 func main() {
-	ch := make(chan os.Signal)
+	ch := make(chan os.Signal, 1)
 	signal.Notify(ch, syscall.SIGUSR2)
 
 	C.register_handler(C.int(syscall.SIGUSR1))

misc/cgo/testsanitizers/testdata/tsan12.go

@@ -22,7 +22,7 @@ import (
 import "C"
 
 func main() {
-	ch := make(chan os.Signal)
+	ch := make(chan os.Signal, 1)
 	signal.Notify(ch, syscall.SIGUSR1)
 
 	if err := exec.Command("true").Run(); err != nil {

src/bytes/bytes.go

@@ -909,7 +909,11 @@ func containsRune(s string, r rune) bool {
 // Trim returns a subslice of s by slicing off all leading and
 // trailing UTF-8-encoded code points contained in cutset.
 func Trim(s []byte, cutset string) []byte {
-	if len(s) == 0 || cutset == "" {
+	if len(s) == 0 {
+		// This is what we've historically done.
+		return nil
+	}
+	if cutset == "" {
 		return s
 	}
 	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
@@ -924,7 +928,11 @@ func Trim(s []byte, cutset string) []byte {
 // TrimLeft returns a subslice of s by slicing off all leading
 // UTF-8-encoded code points contained in cutset.
 func TrimLeft(s []byte, cutset string) []byte {
-	if len(s) == 0 || cutset == "" {
+	if len(s) == 0 {
+		// This is what we've historically done.
+		return nil
+	}
+	if cutset == "" {
 		return s
 	}
 	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
@@ -940,6 +948,10 @@ func trimLeftByte(s []byte, c byte) []byte {
 	for len(s) > 0 && s[0] == c {
 		s = s[1:]
 	}
+	if len(s) == 0 {
+		// This is what we've historically done.
+		return nil
+	}
 	return s
 }
 
@@ -950,6 +962,10 @@ func trimLeftASCII(s []byte, as *asciiSet) []byte {
 		}
 		s = s[1:]
 	}
+	if len(s) == 0 {
+		// This is what we've historically done.
+		return nil
+	}
 	return s
 }
 
@@ -964,6 +980,10 @@ func trimLeftUnicode(s []byte, cutset string) []byte {
 		}
 		s = s[n:]
 	}
+	if len(s) == 0 {
+		// This is what we've historically done.
+		return nil
+	}
 	return s
 }
 

src/bytes/bytes_test.go

@@ -1278,24 +1278,69 @@ var trimTests = []TrimTest{
 	{"TrimSuffix", "aabb", "b", "aab"},
 }
 
+type TrimNilTest struct {
+	f   string
+	in  []byte
+	arg string
+	out []byte
+}
+
+var trimNilTests = []TrimNilTest{
+	{"Trim", nil, "", nil},
+	{"Trim", []byte{}, "", nil},
+	{"Trim", []byte{'a'}, "a", nil},
+	{"Trim", []byte{'a', 'a'}, "a", nil},
+	{"Trim", []byte{'a'}, "ab", nil},
+	{"Trim", []byte{'a', 'b'}, "ab", nil},
+	{"Trim", []byte("☺"), "☺", nil},
+	{"TrimLeft", nil, "", nil},
+	{"TrimLeft", []byte{}, "", nil},
+	{"TrimLeft", []byte{'a'}, "a", nil},
+	{"TrimLeft", []byte{'a', 'a'}, "a", nil},
+	{"TrimLeft", []byte{'a'}, "ab", nil},
+	{"TrimLeft", []byte{'a', 'b'}, "ab", nil},
+	{"TrimLeft", []byte("☺"), "☺", nil},
+	{"TrimRight", nil, "", nil},
+	{"TrimRight", []byte{}, "", []byte{}},
+	{"TrimRight", []byte{'a'}, "a", []byte{}},
+	{"TrimRight", []byte{'a', 'a'}, "a", []byte{}},
+	{"TrimRight", []byte{'a'}, "ab", []byte{}},
+	{"TrimRight", []byte{'a', 'b'}, "ab", []byte{}},
+	{"TrimRight", []byte("☺"), "☺", []byte{}},
+	{"TrimPrefix", nil, "", nil},
+	{"TrimPrefix", []byte{}, "", []byte{}},
+	{"TrimPrefix", []byte{'a'}, "a", []byte{}},
+	{"TrimPrefix", []byte("☺"), "☺", []byte{}},
+	{"TrimSuffix", nil, "", nil},
+	{"TrimSuffix", []byte{}, "", []byte{}},
+	{"TrimSuffix", []byte{'a'}, "a", []byte{}},
+	{"TrimSuffix", []byte("☺"), "☺", []byte{}},
+}
+
 func TestTrim(t *testing.T) {
-	for _, tc := range trimTests {
-		name := tc.f
-		var f func([]byte, string) []byte
-		var fb func([]byte, []byte) []byte
+	toFn := func(name string) (func([]byte, string) []byte, func([]byte, []byte) []byte) {
 		switch name {
 		case "Trim":
-			f = Trim
+			return Trim, nil
 		case "TrimLeft":
-			f = TrimLeft
+			return TrimLeft, nil
 		case "TrimRight":
-			f = TrimRight
+			return TrimRight, nil
 		case "TrimPrefix":
-			fb = TrimPrefix
+			return nil, TrimPrefix
 		case "TrimSuffix":
-			fb = TrimSuffix
+			return nil, TrimSuffix
 		default:
 			t.Errorf("Undefined trim function %s", name)
+			return nil, nil
+		}
+	}
+
+	for _, tc := range trimTests {
+		name := tc.f
+		f, fb := toFn(name)
+		if f == nil && fb == nil {
+			continue
 		}
 		var actual string
 		if f != nil {
@@ -1307,6 +1352,36 @@ func TestTrim(t *testing.T) {
 			t.Errorf("%s(%q, %q) = %q; want %q", name, tc.in, tc.arg, actual, tc.out)
 		}
 	}
+
+	for _, tc := range trimNilTests {
+		name := tc.f
+		f, fb := toFn(name)
+		if f == nil && fb == nil {
+			continue
+		}
+		var actual []byte
+		if f != nil {
+			actual = f(tc.in, tc.arg)
+		} else {
+			actual = fb(tc.in, []byte(tc.arg))
+		}
+		report := func(s []byte) string {
+			if s == nil {
+				return "nil"
+			} else {
+				return fmt.Sprintf("%q", s)
+			}
+		}
+		if len(actual) != 0 {
+			t.Errorf("%s(%s, %q) returned non-empty value", name, report(tc.in), tc.arg)
+		} else {
+			actualNil := actual == nil
+			outNil := tc.out == nil
+			if actualNil != outNil {
+				t.Errorf("%s(%s, %q) got nil %t; want nil %t", name, report(tc.in), tc.arg, actualNil, outNil)
+			}
+		}
+	}
 }
 
 type predicate struct {

src/cmd/compile/internal/amd64/ssa.go

@@ -78,6 +78,8 @@ func storeByType(t *types.Type) obj.As {
 			return x86.AMOVL
 		case 8:
 			return x86.AMOVQ
+		case 16:
+			return x86.AMOVUPS
 		}
 	}
 	panic(fmt.Sprintf("bad store type %v", t))

src/cmd/compile/internal/deadcode/deadcode.go

@@ -163,4 +163,5 @@ func markHiddenClosureDead(n ir.Node) {
 	if clo.Func.IsHiddenClosure() {
 		clo.Func.SetIsDeadcodeClosure(true)
 	}
+	ir.VisitList(clo.Func.Body, markHiddenClosureDead)
 }

src/cmd/compile/internal/dwarfgen/dwarf.go

@@ -91,6 +91,11 @@ func Info(fnsym *obj.LSym, infosym *obj.LSym, curfn interface{}) ([]dwarf.Scope,
 				continue
 			}
 			apdecls = append(apdecls, n)
+			if n.Type().Kind() == types.TSSA {
+				// Can happen for TypeInt128 types. This only happens for
+				// spill locations, so not a huge deal.
+				continue
+			}
 			fnsym.Func().RecordAutoType(reflectdata.TypeLinksym(n.Type()))
 		}
 	}

src/cmd/compile/internal/importer/iimport.go

@@ -53,7 +53,7 @@ const (
 )
 
 type ident struct {
-	pkg  string
+	pkg  *types2.Package
 	name string
 }
 
@@ -402,7 +402,7 @@ func (r *importReader) obj(name string) {
 		t := types2.NewTypeParam(tn, nil)
 		// To handle recursive references to the typeparam within its
 		// bound, save the partial type in tparamIndex before reading the bounds.
-		id := ident{r.currPkg.Name(), name}
+		id := ident{r.currPkg, name}
 		r.p.tparamIndex[id] = t
 
 		var implicit bool
@@ -687,7 +687,7 @@ func (r *importReader) doType(base *types2.Named) types2.Type {
 			errorf("unexpected type param type")
 		}
 		pkg, name := r.qualifiedIdent()
-		id := ident{pkg.Name(), name}
+		id := ident{pkg, name}
 		if t, ok := r.p.tparamIndex[id]; ok {
 			// We're already in the process of importing this typeparam.
 			return t

src/cmd/compile/internal/ir/stmt.go

@@ -362,7 +362,7 @@ func NewSendStmt(pos src.XPos, ch, value Node) *SendStmt {
 	return n
 }
 
-// A SwitchStmt is a switch statement: switch Init; Expr { Cases }.
+// A SwitchStmt is a switch statement: switch Init; Tag { Cases }.
 type SwitchStmt struct {
 	miniStmt
 	Tag      Node

src/cmd/compile/internal/noder/decl.go

@@ -114,11 +114,11 @@ func (g *irgen) funcDecl(out *ir.Nodes, decl *syntax.FuncDecl) {
 		// the Fields to represent the receiver's method set.
 		if recv := fn.Type().Recv(); recv != nil {
 			typ := types.ReceiverBaseType(recv.Type)
-			if typ.OrigSym() != nil {
+			if orig := typ.OrigType(); orig != nil {
 				// For a generic method, we mark the methods on the
 				// base generic type, since those are the methods
 				// that will be stenciled.
-				typ = typ.OrigSym().Def.Type()
+				typ = orig
 			}
 			meth := typecheck.Lookdot1(fn, typecheck.Lookup(decl.Name.Value), typ, typ.Methods(), 0)
 			meth.SetNointerface(true)

src/cmd/compile/internal/noder/stencil.go

@@ -193,8 +193,7 @@ func (g *genInst) scanForGenCalls(decl ir.Node) {
 			targs := deref(meth.Type().Recv().Type).RParams()
 
 			t := meth.X.Type()
-			baseSym := deref(t).OrigSym()
-			baseType := baseSym.Def.(*ir.Name).Type()
+			baseType := deref(t).OrigType()
 			var gf *ir.Name
 			for _, m := range baseType.Methods().Slice() {
 				if meth.Sel == m.Sym {
@@ -348,7 +347,7 @@ func (g *genInst) buildClosure(outer *ir.Func, x ir.Node) ir.Node {
 			// actually generic, so no need to build a closure.
 			return x
 		}
-		baseType := recv.OrigSym().Def.Type()
+		baseType := recv.OrigType()
 		var gf *ir.Name
 		for _, m := range baseType.Methods().Slice() {
 			if se.Sel == m.Sym {
@@ -418,6 +417,7 @@ func (g *genInst) buildClosure(outer *ir.Func, x ir.Node) ir.Node {
 	var dictAssign *ir.AssignStmt
 	if outer != nil {
 		dictVar = ir.NewNameAt(pos, typecheck.LookupNum(typecheck.LocalDictName, g.dnum))
+		dictVar.SetSym(outer.Sym().Pkg.Lookup(dictVar.Sym().Name))
 		g.dnum++
 		dictVar.Class = ir.PAUTO
 		typed(types.Types[types.TUINTPTR], dictVar)
@@ -432,6 +432,9 @@ func (g *genInst) buildClosure(outer *ir.Func, x ir.Node) ir.Node {
 	var rcvrAssign ir.Node
 	if rcvrValue != nil {
 		rcvrVar = ir.NewNameAt(pos, typecheck.LookupNum(".rcvr", g.dnum))
+		if outer != nil {
+			rcvrVar.SetSym(outer.Sym().Pkg.Lookup(rcvrVar.Sym().Name))
+		}
 		g.dnum++
 		typed(rcvrValue.Type(), rcvrVar)
 		rcvrAssign = ir.NewAssignStmt(pos, rcvrVar, rcvrValue)
@@ -543,8 +546,7 @@ func (g *genInst) instantiateMethods() {
 			typecheck.NeedRuntimeType(typ)
 			// Lookup the method on the base generic type, since methods may
 			// not be set on imported instantiated types.
-			baseSym := typ.OrigSym()
-			baseType := baseSym.Def.(*ir.Name).Type()
+			baseType := typ.OrigType()
 			for j, _ := range typ.Methods().Slice() {
 				if baseType.Methods().Slice()[j].Nointerface() {
 					typ.Methods().Slice()[j].SetNointerface(true)
@@ -644,7 +646,7 @@ func (g *genInst) getInstantiation(nameNode *ir.Name, shapes []*types.Type, isMe
 		if recvType.IsFullyInstantiated() {
 			// Get the type of the base generic type, so we get
 			// its original typeparams.
-			recvType = recvType.OrigSym().Def.(*ir.Name).Type()
+			recvType = recvType.OrigType()
 		}
 		tparams = recvType.RParams()
 	} else {
@@ -898,7 +900,7 @@ func getDictionaryType(info *instInfo, dictParam *ir.Name, pos src.XPos, i int)
 		base.Fatalf(fmt.Sprintf("bad dict index %d", i))
 	}
 
-	r := getDictionaryEntry(pos, info.dictParam, i, info.dictInfo.startSubDict)
+	r := getDictionaryEntry(pos, dictParam, i, info.dictInfo.startSubDict)
 	// change type of retrieved dictionary entry to *byte, which is the
 	// standard typing of a *runtime._type in the compiler
 	typed(types.Types[types.TUINT8].PtrTo(), r)
@@ -1179,6 +1181,26 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			subst.g.newInsts = append(subst.g.newInsts, m.(*ir.ClosureExpr).Func)
 			m.(*ir.ClosureExpr).SetInit(subst.list(x.Init()))
 
+		case ir.OSWITCH:
+			m := m.(*ir.SwitchStmt)
+			if m.Tag != nil && m.Tag.Op() == ir.OTYPESW {
+				break // Nothing to do here for type switches.
+			}
+			if m.Tag != nil && !m.Tag.Type().IsEmptyInterface() && m.Tag.Type().HasShape() {
+				// To implement a switch on a value that is or has a type parameter, we first convert
+				// that thing we're switching on to an interface{}.
+				m.Tag = assignconvfn(m.Tag, types.Types[types.TINTER])
+			}
+			for _, c := range m.Cases {
+				for i, x := range c.List {
+					// If we have a case that is or has a type parameter, convert that case
+					// to an interface{}.
+					if !x.Type().IsEmptyInterface() && x.Type().HasShape() {
+						c.List[i] = assignconvfn(x, types.Types[types.TINTER])
+					}
+				}
+			}
+
 		}
 		return m
 	}
@@ -1270,8 +1292,9 @@ func (g *genInst) dictPass(info *instInfo) {
 			mce := m.(*ir.ConvExpr)
 			// Note: x's argument is still typed as a type parameter.
 			// m's argument now has an instantiated type.
-			if mce.X.Type().HasShape() || (mce.X.Type().IsInterface() && m.Type().HasShape()) {
-				m = convertUsingDictionary(info, info.dictParam, m.Pos(), m.(*ir.ConvExpr).X, m, m.Type(), false)
+
+			if mce.X.Type().HasShape() || m.Type().HasShape() {
+				m = convertUsingDictionary(info, info.dictParam, m.Pos(), mce.X, m, m.Type(), false)
 			}
 		case ir.ODOTTYPE, ir.ODOTTYPE2:
 			if !m.Type().HasShape() {
@@ -1367,7 +1390,7 @@ func findDictType(info *instInfo, t *types.Type) int {
 // If nonEscaping is true, the caller guarantees that the backing store needed for the interface data
 // word will not escape.
 func convertUsingDictionary(info *instInfo, dictParam *ir.Name, pos src.XPos, v ir.Node, in ir.Node, dst *types.Type, nonEscaping bool) ir.Node {
-	assert(v.Type().HasShape() || v.Type().IsInterface() && in.Type().HasShape())
+	assert(v.Type().HasShape() || in.Type().HasShape())
 	assert(dst.IsInterface())
 
 	if v.Type().IsInterface() {
@@ -1576,12 +1599,14 @@ func (g *genInst) getDictionarySym(gf *ir.Name, targs []*types.Type, isMeth bool
 				se := call.X.(*ir.SelectorExpr)
 				if se.X.Type().IsShape() {
 					// This is a method call enabled by a type bound.
-
-					// We need this extra check for method expressions,
-					// which don't add in the implicit XDOTs.
-					tmpse := ir.NewSelectorExpr(src.NoXPos, ir.OXDOT, se.X, se.Sel)
-					tmpse = typecheck.AddImplicitDots(tmpse)
-					tparam := tmpse.X.Type()
+					tparam := se.X.Type()
+					if call.X.Op() == ir.ODOTMETH {
+						// We need this extra check for method expressions,
+						// which don't add in the implicit XDOTs.
+						tmpse := ir.NewSelectorExpr(src.NoXPos, ir.OXDOT, se.X, se.Sel)
+						tmpse = typecheck.AddImplicitDots(tmpse)
+						tparam = tmpse.X.Type()
+					}
 					if !tparam.IsShape() {
 						// The method expression is not
 						// really on a typeparam.
@@ -1608,7 +1633,7 @@ func (g *genInst) getDictionarySym(gf *ir.Name, targs []*types.Type, isMeth bool
 					// instantiated type, so we need a
 					// sub-dictionary.
 					targs := recvType.RParams()
-					genRecvType := recvType.OrigSym().Def.Type()
+					genRecvType := recvType.OrigType()
 					nameNode = typecheck.Lookdot1(call.X, se.Sel, genRecvType, genRecvType.Methods(), 1).Nname.(*ir.Name)
 					sym = g.getDictionarySym(nameNode, targs, true)
 				} else {
@@ -1687,7 +1712,7 @@ func (g *genInst) getSymForMethodCall(se *ir.SelectorExpr, subst *typecheck.Tsub
 	// also give the receiver type. For method expressions with embedded types, we
 	// need to look at the type of the selection to get the final receiver type.
 	recvType := deref(se.Selection.Type.Recv().Type)
-	genRecvType := recvType.OrigSym().Def.Type()
+	genRecvType := recvType.OrigType()
 	nameNode := typecheck.Lookdot1(se, se.Sel, genRecvType, genRecvType.Methods(), 1).Nname.(*ir.Name)
 	subtargs := recvType.RParams()
 	s2targs := make([]*types.Type, len(subtargs))
@@ -1746,6 +1771,7 @@ func (g *genInst) finalizeSyms() {
 				g.instantiateMethods()
 				itabLsym := reflectdata.ITabLsym(srctype, dsttype)
 				d.off = objw.SymPtr(lsym, d.off, itabLsym, 0)
+				markTypeUsed(srctype, lsym)
 				infoPrint(" + Itab for (%v,%v)\n", srctype, dsttype)
 			}
 		}
@@ -1896,7 +1922,7 @@ func (g *genInst) getInstInfo(st *ir.Func, shapes []*types.Type, instInfo *instI
 			}
 		case ir.OCONVIFACE:
 			if n.Type().IsInterface() && !n.Type().IsEmptyInterface() &&
-				n.(*ir.ConvExpr).X.Type().HasShape() {
+				(n.Type().HasShape() || n.(*ir.ConvExpr).X.Type().HasShape()) {
 				infoPrint("  Itab for interface conv: %v\n", n)
 				info.itabConvs = append(info.itabConvs, n)
 			}
@@ -2091,6 +2117,9 @@ func startClosure(pos src.XPos, outer *ir.Func, typ *types.Type) (*ir.Func, []*t
 	for i := 0; i < typ.NumParams(); i++ {
 		t := typ.Params().Field(i).Type
 		arg := ir.NewNameAt(pos, typecheck.LookupNum("a", i))
+		if outer != nil {
+			arg.SetSym(outer.Sym().Pkg.Lookup(arg.Sym().Name))
+		}
 		arg.Class = ir.PPARAM
 		typed(t, arg)
 		arg.Curfn = fn
@@ -2103,6 +2132,9 @@ func startClosure(pos src.XPos, outer *ir.Func, typ *types.Type) (*ir.Func, []*t
 	for i := 0; i < typ.NumResults(); i++ {
 		t := typ.Results().Field(i).Type
 		result := ir.NewNameAt(pos, typecheck.LookupNum("r", i)) // TODO: names not needed?
+		if outer != nil {
+			result.SetSym(outer.Sym().Pkg.Lookup(result.Sym().Name))
+		}
 		result.Class = ir.PPARAMOUT
 		typed(t, result)
 		result.Curfn = fn

src/cmd/compile/internal/noder/transform.go

@@ -242,7 +242,7 @@ func transformCompare(n *ir.BinaryExpr) {
 			aop, _ := typecheck.Assignop(rt, lt)
 			if aop != ir.OXXX {
 				types.CalcSize(rt)
-				if rt.HasTParam() || rt.IsInterface() == lt.IsInterface() || rt.Size() >= 1<<16 {
+				if rt.HasShape() || rt.IsInterface() == lt.IsInterface() || rt.Size() >= 1<<16 {
 					r = ir.NewConvExpr(base.Pos, aop, lt, r)
 					r.SetTypecheck(1)
 				}

src/cmd/compile/internal/noder/types.go

@@ -166,7 +166,7 @@ func (g *irgen) typ0(typ types2.Type) *types.Type {
 			//fmt.Printf("Saw new type %v %v\n", instName, ntyp.HasTParam())
 
 			// Save the symbol for the base generic type.
-			ntyp.SetOrigSym(g.pkg(typ.Obj().Pkg()).Lookup(typ.Obj().Name()))
+			ntyp.SetOrigType(base.Type())
 			ntyp.SetUnderlying(g.typ1(typ.Underlying()))
 			if typ.NumMethods() != 0 {
 				// Save a delayed call to g.fillinMethods() (once

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1321,21 +1321,21 @@ func writeITab(lsym *obj.LSym, typ, iface *types.Type, allowNonImplement bool) {
 	// type itab struct {
 	//   inter  *interfacetype
 	//   _type  *_type
-	//   hash   uint32
+	//   hash   uint32 // copy of _type.hash. Used for type switches.
 	//   _      [4]byte
-	//   fun    [1]uintptr // variable sized
+	//   fun    [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
 	// }
 	o := objw.SymPtr(lsym, 0, writeType(iface), 0)
 	o = objw.SymPtr(lsym, o, writeType(typ), 0)
 	o = objw.Uint32(lsym, o, types.TypeHash(typ)) // copy of type hash
 	o += 4                                        // skip unused field
+	if !completeItab {
+		// If typ doesn't implement iface, make method entries be zero.
+		o = objw.Uintptr(lsym, o, 0)
+		entries = entries[:0]
+	}
 	for _, fn := range entries {
-		if !completeItab {
-			// If typ doesn't implement iface, make method entries be zero.
-			o = objw.Uintptr(lsym, o, 0)
-		} else {
-			o = objw.SymPtrWeak(lsym, o, fn, 0) // method pointer for each method
-		}
+		o = objw.SymPtrWeak(lsym, o, fn, 0) // method pointer for each method
 	}
 	// Nothing writes static itabs, so they are read only.
 	objw.Global(lsym, int32(o), int16(obj.DUPOK|obj.RODATA))
@@ -1430,7 +1430,7 @@ func WriteBasicTypes() {
 
 type typeAndStr struct {
 	t       *types.Type
-	short   string // "short" here means NameString
+	short   string // "short" here means TypeSymName
 	regular string
 }
 
@@ -1921,7 +1921,7 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 
 			// Target method uses shaped names.
 			targs2 := make([]*types.Type, len(targs))
-			origRParams := deref(orig).OrigSym().Def.(*ir.Name).Type().RParams()
+			origRParams := deref(orig).OrigType().RParams()
 			for i, t := range targs {
 				targs2[i] = typecheck.Shapify(t, i, origRParams[i])
 			}

src/cmd/compile/internal/ssa/loopbce.go

@@ -159,6 +159,13 @@ func findIndVar(f *Func) []indVar {
 			step = -step
 		}
 
+		if flags&indVarMaxInc != 0 && max.Op == OpConst64 && max.AuxInt+step < max.AuxInt {
+			// For a <= comparison, we need to make sure that a value equal to
+			// max can be incremented without overflowing.
+			// (For a < comparison, the %step check below ensures no overflow.)
+			continue
+		}
+
 		// Up to now we extracted the induction variable (ind),
 		// the increment delta (inc), the temporary sum (nxt),
 		// the mininum value (min) and the maximum value (max).

src/cmd/compile/internal/ssa/rewrite.go

@@ -40,6 +40,7 @@ func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter, deadcode deadValu
 	var states map[string]bool
 	for {
 		change := false
+		deadChange := false
 		for _, b := range f.Blocks {
 			var b0 *Block
 			if debug > 1 {
@@ -73,7 +74,7 @@ func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter, deadcode deadValu
 						// Not quite a deadcode pass, because it does not handle cycles.
 						// But it should help Uses==1 rules to fire.
 						v.reset(OpInvalid)
-						change = true
+						deadChange = true
 					}
 					// No point rewriting values which aren't used.
 					continue
@@ -145,15 +146,16 @@ func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter, deadcode deadValu
 				}
 			}
 		}
-		if !change {
+		if !change && !deadChange {
 			break
 		}
 		iters++
-		if iters > 1000 || debug >= 2 {
+		if (iters > 1000 || debug >= 2) && change {
 			// We've done a suspiciously large number of rewrites (or we're in debug mode).
 			// As of Sep 2021, 90% of rewrites complete in 4 iterations or fewer
 			// and the maximum value encountered during make.bash is 12.
 			// Start checking for cycles. (This is too expensive to do routinely.)
+			// Note: we avoid this path for deadChange-only iterations, to fix #51639.
 			if states == nil {
 				states = make(map[string]bool)
 			}

src/cmd/compile/internal/typecheck/const.go

@@ -895,6 +895,18 @@ func evalunsafe(n ir.Node) int64 {
 		sel.X = Expr(sel.X)
 		sbase := sel.X
 
+		// Implicit dot may already be resolved for instantiating generic function. So we
+		// need to remove any implicit dot until we reach the first non-implicit one, it's
+		// the right base selector. See issue #53137.
+		var clobberBase func(n ir.Node) ir.Node
+		clobberBase = func(n ir.Node) ir.Node {
+			if sel, ok := n.(*ir.SelectorExpr); ok && sel.Implicit() {
+				return clobberBase(sel.X)
+			}
+			return n
+		}
+		sbase = clobberBase(sbase)
+
 		tsel := Expr(sel)
 		n.X = tsel
 		if tsel.Type() == nil {

src/cmd/compile/internal/typecheck/crawler.go

@@ -66,9 +66,9 @@ func (p *crawler) markObject(n *ir.Name) {
 // inline bodies may be needed. For instantiated generic types, it visits the base
 // generic type, which has the relevant methods.
 func (p *crawler) markType(t *types.Type) {
-	if t.OrigSym() != nil {
+	if orig := t.OrigType(); orig != nil {
 		// Convert to the base generic type.
-		t = t.OrigSym().Def.Type()
+		t = orig
 	}
 	if p.marked[t] {
 		return
@@ -154,9 +154,9 @@ func (p *crawler) markEmbed(t *types.Type) {
 		t = t.Elem()
 	}
 
-	if t.OrigSym() != nil {
+	if orig := t.OrigType(); orig != nil {
 		// Convert to the base generic type.
-		t = t.OrigSym().Def.Type()
+		t = orig
 	}
 
 	if p.embedded[t] {
@@ -194,9 +194,9 @@ func (p *crawler) markGeneric(t *types.Type) {
 	if t.IsPtr() {
 		t = t.Elem()
 	}
-	if t.OrigSym() != nil {
+	if orig := t.OrigType(); orig != nil {
 		// Convert to the base generic type.
-		t = t.OrigSym().Def.Type()
+		t = orig
 	}
 	if p.generic[t] {
 		return
@@ -229,12 +229,12 @@ func (p *crawler) checkForFullyInst(t *types.Type) {
 		// them available for import, and so will not need
 		// another round of method and dictionary
 		// instantiation after inlining.
-		baseType := t.OrigSym().Def.(*ir.Name).Type()
+		baseType := t.OrigType()
 		shapes := make([]*types.Type, len(t.RParams()))
 		for i, t1 := range t.RParams() {
 			shapes[i] = Shapify(t1, i, baseType.RParams()[i])
 		}
-		for j := range t.Methods().Slice() {
+		for j, tmethod := range t.Methods().Slice() {
 			baseNname := baseType.Methods().Slice()[j].Nname.(*ir.Name)
 			dictsym := MakeDictSym(baseNname.Sym(), t.RParams(), true)
 			if dictsym.Def == nil {
@@ -255,6 +255,8 @@ func (p *crawler) checkForFullyInst(t *types.Type) {
 				ImportedBody(methNode.Func)
 				methNode.Func.SetExportInline(true)
 			}
+			// Make sure that any associated types are also exported. (See #52279)
+			p.checkForFullyInst(tmethod.Type)
 		}
 	}
 

src/cmd/compile/internal/typecheck/iexport.go

@@ -953,7 +953,7 @@ func (w *exportWriter) startType(k itag) {
 
 func (w *exportWriter) doTyp(t *types.Type) {
 	s := t.Sym()
-	if s != nil && t.OrigSym() != nil {
+	if s != nil && t.OrigType() != nil {
 		assert(base.Flag.G > 0)
 		// This is an instantiated type - could be a re-instantiation like
 		// Value[T2] or a full instantiation like Value[int].
@@ -970,7 +970,7 @@ func (w *exportWriter) doTyp(t *types.Type) {
 		// types or existing typeparams from the function/method header.
 		w.typeList(t.RParams())
 		// Export a reference to the base type.
-		baseType := t.OrigSym().Def.(*ir.Name).Type()
+		baseType := t.OrigType()
 		w.typ(baseType)
 		return
 	}
@@ -1851,7 +1851,10 @@ func (w *exportWriter) expr(n ir.Node) {
 		n := n.(*ir.ClosureExpr)
 		w.op(ir.OCLOSURE)
 		w.pos(n.Pos())
+		old := w.currPkg
+		w.setPkg(n.Type().Pkg(), true)
 		w.signature(n.Type())
+		w.setPkg(old, true)
 
 		// Write out id for the Outer of each conditional variable. The
 		// conditional variable itself for this closure will be re-created
@@ -2281,7 +2284,7 @@ func (w *exportWriter) localIdent(s *types.Sym) {
 		return
 	}
 
-	if i := strings.LastIndex(name, "."); i >= 0 && !strings.HasPrefix(name, LocalDictName) {
+	if i := strings.LastIndex(name, "."); i >= 0 && !strings.HasPrefix(name, LocalDictName) && !strings.HasPrefix(name, ".rcvr") {
 		base.Fatalf("unexpected dot in identifier: %v", name)
 	}
 

src/cmd/compile/internal/typecheck/iimport.go

@@ -761,7 +761,7 @@ func (p *iimporter) typAt(off uint64) *types.Type {
 		// No need to calc sizes for re-instantiated generic types, and
 		// they are not necessarily resolved until the top-level type is
 		// defined (because of recursive types).
-		if t.OrigSym() == nil || !t.HasTParam() {
+		if t.OrigType() == nil || !t.HasTParam() {
 			types.CheckSize(t)
 		}
 		p.typCache[off] = t
@@ -1374,7 +1374,9 @@ func (r *importReader) node() ir.Node {
 	case ir.OCLOSURE:
 		//println("Importing CLOSURE")
 		pos := r.pos()
+		r.setPkg()
 		typ := r.signature(nil, nil)
+		r.setPkg()
 
 		// All the remaining code below is similar to (*noder).funcLit(), but
 		// with Dcls and ClosureVars lists already set up
@@ -1480,7 +1482,7 @@ func (r *importReader) node() ir.Node {
 					} else {
 						genType := types.ReceiverBaseType(n1.X.Type())
 						if genType.IsInstantiatedGeneric() {
-							genType = genType.OrigSym().Def.Type()
+							genType = genType.OrigType()
 						}
 						m = Lookdot1(n1, sel, genType, genType.Methods(), 1)
 					}
@@ -1911,7 +1913,7 @@ func Instantiate(pos src.XPos, baseType *types.Type, targs []*types.Type) *types
 
 	t := NewIncompleteNamedType(baseType.Pos(), instSym)
 	t.SetRParams(targs)
-	t.SetOrigSym(baseSym)
+	t.SetOrigType(baseType)
 
 	// baseType may still be TFORW or its methods may not be fully filled in
 	// (since we are in the middle of importing it). So, delay call to
@@ -1936,7 +1938,7 @@ func resumeDoInst() {
 		for len(deferredInstStack) > 0 {
 			t := deferredInstStack[0]
 			deferredInstStack = deferredInstStack[1:]
-			substInstType(t, t.OrigSym().Def.(*ir.Name).Type(), t.RParams())
+			substInstType(t, t.OrigType(), t.RParams())
 		}
 	}
 	deferInst--
@@ -1948,7 +1950,7 @@ func resumeDoInst() {
 // instantiations of mutually recursive types.
 func doInst(t *types.Type) *types.Type {
 	assert(t.Kind() == types.TFORW)
-	return Instantiate(t.Pos(), t.OrigSym().Def.(*ir.Name).Type(), t.RParams())
+	return Instantiate(t.Pos(), t.OrigType(), t.RParams())
 }
 
 // substInstType completes the instantiation of a generic type by doing a

src/cmd/compile/internal/typecheck/subr.go

@@ -1120,10 +1120,10 @@ func (ts *Tsubster) typ1(t *types.Type) *types.Type {
 		forw = NewIncompleteNamedType(t.Pos(), newsym)
 		//println("Creating new type by sub", newsym.Name, forw.HasTParam())
 		forw.SetRParams(neededTargs)
-		// Copy the OrigSym from the re-instantiated type (which is the sym of
+		// Copy the OrigType from the re-instantiated type (which is the sym of
 		// the base generic type).
-		assert(t.OrigSym() != nil)
-		forw.SetOrigSym(t.OrigSym())
+		assert(t.OrigType() != nil)
+		forw.SetOrigType(t.OrigType())
 	}
 
 	var newt *types.Type
@@ -1536,7 +1536,7 @@ func Shapify(t *types.Type, index int, tparam *types.Type) *types.Type {
 	// Note: pointers to arrays are special because of slice-to-array-pointer
 	// conversions. See issue 49295.
 	if u.Kind() == types.TPTR && u.Elem().Kind() != types.TARRAY &&
-		tparam.Bound().StructuralType() == nil {
+		tparam.Bound().StructuralType() == nil && !u.Elem().NotInHeap() {
 		u = types.Types[types.TUINT8].PtrTo()
 	}
 

src/cmd/compile/internal/types/fmt.go

@@ -72,6 +72,7 @@ const (
 	fmtDebug
 	fmtTypeID
 	fmtTypeIDName
+	fmtTypeIDHash
 )
 
 // Sym
@@ -144,10 +145,21 @@ func symfmt(b *bytes.Buffer, s *Sym, verb rune, mode fmtMode) {
 	if q := pkgqual(s.Pkg, verb, mode); q != "" {
 		b.WriteString(q)
 		b.WriteByte('.')
-		if mode == fmtTypeIDName {
+		switch mode {
+		case fmtTypeIDName:
 			// If name is a generic instantiation, it might have local package placeholders
 			// in it. Replace those placeholders with the package name. See issue 49547.
 			name = strings.Replace(name, LocalPkg.Prefix, q, -1)
+		case fmtTypeIDHash:
+			// If name is a generic instantiation, don't hash the instantiating types.
+			// This isn't great, but it is safe. If we hash the instantiating types, then
+			// we need to make sure they have just the package name. At this point, they
+			// either have "", or the whole package path, and it is hard to reconcile
+			// the two without depending on -p (which we might do someday).
+			// See issue 51250.
+			if i := strings.Index(name, "["); i >= 0 {
+				name = name[:i]
+			}
 		}
 	}
 	b.WriteString(name)
@@ -173,7 +185,7 @@ func pkgqual(pkg *Pkg, verb rune, mode fmtMode) string {
 		case fmtDebug:
 			return pkg.Name
 
-		case fmtTypeIDName:
+		case fmtTypeIDName, fmtTypeIDHash:
 			// dcommontype, typehash
 			return pkg.Name
 
@@ -331,7 +343,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 	if t == AnyType || t == ByteType || t == RuneType {
 		// in %-T mode collapse predeclared aliases with their originals.
 		switch mode {
-		case fmtTypeIDName, fmtTypeID:
+		case fmtTypeIDName, fmtTypeIDHash, fmtTypeID:
 			t = Types[t.Kind()]
 		default:
 			sconv2(b, t.Sym(), 'S', mode)
@@ -422,7 +434,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 	case TPTR:
 		b.WriteByte('*')
 		switch mode {
-		case fmtTypeID, fmtTypeIDName:
+		case fmtTypeID, fmtTypeIDName, fmtTypeIDHash:
 			if verb == 'S' {
 				tconv2(b, t.Elem(), 'S', mode, visited)
 				return
@@ -484,7 +496,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 			case IsExported(f.Sym.Name):
 				sconv2(b, f.Sym, 'S', mode)
 			default:
-				if mode != fmtTypeIDName {
+				if mode != fmtTypeIDName && mode != fmtTypeIDHash {
 					mode = fmtTypeID
 				}
 				sconv2(b, f.Sym, 'v', mode)
@@ -554,7 +566,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 			b.WriteByte(byte(open))
 			fieldVerb := 'v'
 			switch mode {
-			case fmtTypeID, fmtTypeIDName, fmtGo:
+			case fmtTypeID, fmtTypeIDName, fmtTypeIDHash, fmtGo:
 				// no argument names on function signature, and no "noescape"/"nosplit" tags
 				fieldVerb = 'S'
 			}
@@ -688,7 +700,7 @@ func fldconv(b *bytes.Buffer, f *Field, verb rune, mode fmtMode, visited map[*Ty
 				if name == ".F" {
 					name = "F" // Hack for toolstash -cmp.
 				}
-				if !IsExported(name) && mode != fmtTypeIDName {
+				if !IsExported(name) && mode != fmtTypeIDName && mode != fmtTypeIDHash {
 					name = sconv(s, 0, mode) // qualify non-exported names (used on structs, not on funarg)
 				}
 			} else {
@@ -756,7 +768,7 @@ func FmtConst(v constant.Value, sharp bool) string {
 
 // TypeHash computes a hash value for type t to use in type switch statements.
 func TypeHash(t *Type) uint32 {
-	p := t.NameString()
+	p := tconv(t, 0, fmtTypeIDHash)
 
 	// Using MD5 is overkill, but reduces accidental collisions.
 	h := md5.Sum([]byte(p))

src/cmd/compile/internal/types/size.go

@@ -696,6 +696,12 @@ func PtrDataSize(t *Type) int64 {
 		}
 		return 0
 
+	case TSSA:
+		if t != TypeInt128 {
+			base.Fatalf("PtrDataSize: unexpected ssa type %v", t)
+		}
+		return 0
+
 	default:
 		base.Fatalf("PtrDataSize: unexpected type, %v", t)
 		return 0

src/cmd/compile/internal/types/type.go

@@ -202,10 +202,10 @@ type Type struct {
 	// TODO(danscales): choose a better name.
 	rparams *[]*Type
 
-	// For an instantiated generic type, the symbol for the base generic type.
+	// For an instantiated generic type, the base generic type.
 	// This backpointer is useful, because the base type is the type that has
 	// the method bodies.
-	origSym *Sym
+	origType *Type
 }
 
 func (*Type) CanBeAnSSAAux() {}
@@ -250,10 +250,10 @@ func (t *Type) Kind() Kind { return t.kind }
 func (t *Type) Sym() *Sym       { return t.sym }
 func (t *Type) SetSym(sym *Sym) { t.sym = sym }
 
-// OrigSym returns the name of the original generic type that t is an
+// OrigType returns the original generic type that t is an
 // instantiation of, if any.
-func (t *Type) OrigSym() *Sym       { return t.origSym }
-func (t *Type) SetOrigSym(sym *Sym) { t.origSym = sym }
+func (t *Type) OrigType() *Type        { return t.origType }
+func (t *Type) SetOrigType(orig *Type) { t.origType = orig }
 
 // Underlying returns the underlying type of type t.
 func (t *Type) Underlying() *Type { return t.underlying }
@@ -1721,6 +1721,11 @@ var (
 	TypeResultMem = newResults([]*Type{TypeMem})
 )
 
+func init() {
+	TypeInt128.width = 16
+	TypeInt128.align = 8
+}
+
 // NewNamed returns a new named type for the given type name. obj should be an
 // ir.Name. The new type is incomplete (marked as TFORW kind), and the underlying
 // type should be set later via SetUnderlying(). References to the type are

src/cmd/compile/internal/types2/api.go

@@ -204,12 +204,12 @@ type Info struct {
 	// qualified identifiers are collected in the Uses map.
 	Types map[syntax.Expr]TypeAndValue
 
-	// Instances maps identifiers denoting parameterized types or functions to
-	// their type arguments and instantiated type.
+	// Instances maps identifiers denoting generic types or functions to their
+	// type arguments and instantiated type.
 	//
 	// For example, Instances will map the identifier for 'T' in the type
 	// instantiation T[int, string] to the type arguments [int, string] and
-	// resulting instantiated *Named type. Given a parameterized function
+	// resulting instantiated *Named type. Given a generic function
 	// func F[A any](A), Instances will map the identifier for 'F' in the call
 	// expression F(int(1)) to the inferred type arguments [int], and resulting
 	// instantiated *Signature.
@@ -421,8 +421,11 @@ func (conf *Config) Check(path string, files []*syntax.File, info *Info) (*Packa
 }
 
 // AssertableTo reports whether a value of type V can be asserted to have type T.
-// The behavior of AssertableTo is undefined if V is a generalized interface; i.e.,
-// an interface that may only be used as a type constraint in Go code.
+//
+// The behavior of AssertableTo is undefined in two cases:
+//  - if V is a generalized interface; i.e., an interface that may only be used
+//    as a type constraint in Go code
+//  - if T is an uninstantiated generic type
 func AssertableTo(V *Interface, T Type) bool {
 	// Checker.newAssertableTo suppresses errors for invalid types, so we need special
 	// handling here.
@@ -432,20 +435,31 @@ func AssertableTo(V *Interface, T Type) bool {
 	return (*Checker)(nil).newAssertableTo(V, T) == nil
 }
 
-// AssignableTo reports whether a value of type V is assignable to a variable of type T.
+// AssignableTo reports whether a value of type V is assignable to a variable
+// of type T.
+//
+// The behavior of AssignableTo is undefined if V or T is an uninstantiated
+// generic type.
 func AssignableTo(V, T Type) bool {
 	x := operand{mode: value, typ: V}
 	ok, _ := x.assignableTo(nil, T, nil) // check not needed for non-constant x
 	return ok
 }
 
-// ConvertibleTo reports whether a value of type V is convertible to a value of type T.
+// ConvertibleTo reports whether a value of type V is convertible to a value of
+// type T.
+//
+// The behavior of ConvertibleTo is undefined if V or T is an uninstantiated
+// generic type.
 func ConvertibleTo(V, T Type) bool {
 	x := operand{mode: value, typ: V}
 	return x.convertibleTo(nil, T, nil) // check not needed for non-constant x
 }
 
 // Implements reports whether type V implements interface T.
+//
+// The behavior of Implements is undefined if V is an uninstantiated generic
+// type.
 func Implements(V Type, T *Interface) bool {
 	if T.Empty() {
 		// All types (even Typ[Invalid]) implement the empty interface.

src/cmd/compile/internal/types2/api_test.go

@@ -12,6 +12,7 @@ import (
 	"internal/testenv"
 	"reflect"
 	"regexp"
+	"sort"
 	"strings"
 	"testing"
 
@@ -403,69 +404,61 @@ func TestTypesInfo(t *testing.T) {
 }
 
 func TestInstanceInfo(t *testing.T) {
-	var tests = []struct {
-		src   string
+	const lib = `package lib
+
+func F[P any](P) {}
+
+type T[P any] []P
+`
+
+	type testInst struct {
 		name  string
 		targs []string
 		typ   string
+	}
+
+	var tests = []struct {
+		src       string
+		instances []testInst // recorded instances in source order
 	}{
 		{`package p0; func f[T any](T) {}; func _() { f(42) }`,
-			`f`,
-			[]string{`int`},
-			`func(int)`,
+			[]testInst{{`f`, []string{`int`}, `func(int)`}},
 		},
 		{`package p1; func f[T any](T) T { panic(0) }; func _() { f('@') }`,
-			`f`,
-			[]string{`rune`},
-			`func(rune) rune`,
+			[]testInst{{`f`, []string{`rune`}, `func(rune) rune`}},
 		},
 		{`package p2; func f[T any](...T) T { panic(0) }; func _() { f(0i) }`,
-			`f`,
-			[]string{`complex128`},
-			`func(...complex128) complex128`,
+			[]testInst{{`f`, []string{`complex128`}, `func(...complex128) complex128`}},
 		},
 		{`package p3; func f[A, B, C any](A, *B, []C) {}; func _() { f(1.2, new(string), []byte{}) }`,
-			`f`,
-			[]string{`float64`, `string`, `byte`},
-			`func(float64, *string, []byte)`,
+			[]testInst{{`f`, []string{`float64`, `string`, `byte`}, `func(float64, *string, []byte)`}},
 		},
 		{`package p4; func f[A, B any](A, *B, ...[]B) {}; func _() { f(1.2, new(byte)) }`,
-			`f`,
-			[]string{`float64`, `byte`},
-			`func(float64, *byte, ...[]byte)`,
+			[]testInst{{`f`, []string{`float64`, `byte`}, `func(float64, *byte, ...[]byte)`}},
 		},
-
 		// we don't know how to translate these but we can type-check them
 		{`package q0; type T struct{}; func (T) m[P any](P) {}; func _(x T) { x.m(42) }`,
-			`m`,
-			[]string{`int`},
-			`func(int)`,
+			[]testInst{{`m`, []string{`int`}, `func(int)`}},
 		},
 		{`package q1; type T struct{}; func (T) m[P any](P) P { panic(0) }; func _(x T) { x.m(42) }`,
-			`m`,
-			[]string{`int`},
-			`func(int) int`,
+			[]testInst{{`m`, []string{`int`}, `func(int) int`}},
 		},
 		{`package q2; type T struct{}; func (T) m[P any](...P) P { panic(0) }; func _(x T) { x.m(42) }`,
-			`m`,
-			[]string{`int`},
-			`func(...int) int`,
+			[]testInst{{`m`, []string{`int`}, `func(...int) int`}},
 		},
 		{`package q3; type T struct{}; func (T) m[A, B, C any](A, *B, []C) {}; func _(x T) { x.m(1.2, new(string), []byte{}) }`,
-			`m`,
-			[]string{`float64`, `string`, `byte`},
-			`func(float64, *string, []byte)`,
+			[]testInst{{`m`, []string{`float64`, `string`, `byte`}, `func(float64, *string, []byte)`}},
 		},
 		{`package q4; type T struct{}; func (T) m[A, B any](A, *B, ...[]B) {}; func _(x T) { x.m(1.2, new(byte)) }`,
-			`m`,
-			[]string{`float64`, `byte`},
-			`func(float64, *byte, ...[]byte)`,
+			[]testInst{{`m`, []string{`float64`, `byte`}, `func(float64, *byte, ...[]byte)`}},
 		},
 
-		{`package r0; type T[P any] struct{}; func (_ T[P]) m[Q any](Q) {}; func _[P any](x T[P]) { x.m(42) }`,
-			`m`,
-			[]string{`int`},
-			`func(int)`,
+		{`package r0; type T[P1 any] struct{}; func (_ T[P2]) m[Q any](Q) {}; func _[P3 any](x T[P3]) { x.m(42) }`,
+			[]testInst{
+				{`T`, []string{`P2`}, `struct{}`},
+				{`T`, []string{`P3`}, `struct{}`},
+				{`m`, []string{`int`}, `func(int)`},
+			},
 		},
 		// TODO(gri) record method type parameters in syntax.FuncType so we can check this
 		// {`package r1; type T interface{ m[P any](P) }; func _(x T) { x.m(4.2) }`,
@@ -474,97 +467,113 @@ func TestInstanceInfo(t *testing.T) {
 		// 	`func(float64)`,
 		// },
 
-		{`package s1; func f[T any, P interface{~*T}](x T) {}; func _(x string) { f(x) }`,
-			`f`,
-			[]string{`string`, `*string`},
-			`func(x string)`,
+		{`package s1; func f[T any, P interface{*T}](x T) {}; func _(x string) { f(x) }`,
+			[]testInst{{`f`, []string{`string`, `*string`}, `func(x string)`}},
 		},
-		{`package s2; func f[T any, P interface{~*T}](x []T) {}; func _(x []int) { f(x) }`,
-			`f`,
-			[]string{`int`, `*int`},
-			`func(x []int)`,
+		{`package s2; func f[T any, P interface{*T}](x []T) {}; func _(x []int) { f(x) }`,
+			[]testInst{{`f`, []string{`int`, `*int`}, `func(x []int)`}},
 		},
-		{`package s3; type C[T any] interface{~chan<- T}; func f[T any, P C[T]](x []T) {}; func _(x []int) { f(x) }`,
-			`f`,
-			[]string{`int`, `chan<- int`},
-			`func(x []int)`,
+		{`package s3; type C[T any] interface{chan<- T}; func f[T any, P C[T]](x []T) {}; func _(x []int) { f(x) }`,
+			[]testInst{
+				{`C`, []string{`T`}, `interface{chan<- T}`},
+				{`f`, []string{`int`, `chan<- int`}, `func(x []int)`},
+			},
 		},
-		{`package s4; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T) {}; func _(x []int) { f(x) }`,
-			`f`,
-			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
-			`func(x []int)`,
+		{`package s4; type C[T any] interface{chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T) {}; func _(x []int) { f(x) }`,
+			[]testInst{
+				{`C`, []string{`T`}, `interface{chan<- T}`},
+				{`C`, []string{`[]*P`}, `interface{chan<- []*P}`},
+				{`f`, []string{`int`, `chan<- int`, `chan<- []*chan<- int`}, `func(x []int)`},
+			},
 		},
 
-		{`package t1; func f[T any, P interface{~*T}]() T { panic(0) }; func _() { _ = f[string] }`,
-			`f`,
-			[]string{`string`, `*string`},
-			`func() string`,
+		{`package t1; func f[T any, P interface{*T}]() T { panic(0) }; func _() { _ = f[string] }`,
+			[]testInst{{`f`, []string{`string`, `*string`}, `func() string`}},
 		},
-		{`package t2; func f[T any, P interface{~*T}]() T { panic(0) }; func _() { _ = (f[string]) }`,
-			`f`,
-			[]string{`string`, `*string`},
-			`func() string`,
+		{`package t2; func f[T any, P interface{*T}]() T { panic(0) }; func _() { _ = (f[string]) }`,
+			[]testInst{{`f`, []string{`string`, `*string`}, `func() string`}},
 		},
-		{`package t3; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T { return nil }; func _() { _ = f[int] }`,
-			`f`,
-			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
-			`func() []int`,
+		{`package t3; type C[T any] interface{chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T { return nil }; func _() { _ = f[int] }`,
+			[]testInst{
+				{`C`, []string{`T`}, `interface{chan<- T}`},
+				{`C`, []string{`[]*P`}, `interface{chan<- []*P}`},
+				{`f`, []string{`int`, `chan<- int`, `chan<- []*chan<- int`}, `func() []int`},
+			},
 		},
-		{`package t4; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T { return nil }; func _() { _ = f[int] }`,
-			`f`,
-			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
-			`func() []int`,
+		{`package t4; type C[T any] interface{chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T { return nil }; func _() { _ = (f[int]) }`,
+			[]testInst{
+				{`C`, []string{`T`}, `interface{chan<- T}`},
+				{`C`, []string{`[]*P`}, `interface{chan<- []*P}`},
+				{`f`, []string{`int`, `chan<- int`, `chan<- []*chan<- int`}, `func() []int`},
+			},
 		},
-		{`package i0; import lib "generic_lib"; func _() { lib.F(42) }`,
-			`F`,
-			[]string{`int`},
-			`func(int)`,
+		{`package i0; import "lib"; func _() { lib.F(42) }`,
+			[]testInst{{`F`, []string{`int`}, `func(int)`}},
 		},
+
+		{`package duplfunc0; func f[T any](T) {}; func _() { f(42); f("foo"); f[int](3) }`,
+			[]testInst{
+				{`f`, []string{`int`}, `func(int)`},
+				{`f`, []string{`string`}, `func(string)`},
+				{`f`, []string{`int`}, `func(int)`},
+			},
+		},
+		{`package duplfunc1; import "lib"; func _() { lib.F(42); lib.F("foo"); lib.F(3) }`,
+			[]testInst{
+				{`F`, []string{`int`}, `func(int)`},
+				{`F`, []string{`string`}, `func(string)`},
+				{`F`, []string{`int`}, `func(int)`},
+			},
+		},
+
 		{`package type0; type T[P interface{~int}] struct{ x P }; var _ T[int]`,
-			`T`,
-			[]string{`int`},
-			`struct{x int}`,
+			[]testInst{{`T`, []string{`int`}, `struct{x int}`}},
 		},
 		{`package type1; type T[P interface{~int}] struct{ x P }; var _ (T[int])`,
-			`T`,
-			[]string{`int`},
-			`struct{x int}`,
+			[]testInst{{`T`, []string{`int`}, `struct{x int}`}},
 		},
 		{`package type2; type T[P interface{~int}] struct{ x P }; var _ T[(int)]`,
-			`T`,
-			[]string{`int`},
-			`struct{x int}`,
+			[]testInst{{`T`, []string{`int`}, `struct{x int}`}},
 		},
 		{`package type3; type T[P1 interface{~[]P2}, P2 any] struct{ x P1; y P2 }; var _ T[[]int, int]`,
-			`T`,
-			[]string{`[]int`, `int`},
-			`struct{x []int; y int}`,
+			[]testInst{{`T`, []string{`[]int`, `int`}, `struct{x []int; y int}`}},
 		},
-		{`package type4; import lib "generic_lib"; var _ lib.T[int]`,
-			`T`,
-			[]string{`int`},
-			`[]int`,
+		{`package type4; import "lib"; var _ lib.T[int]`,
+			[]testInst{{`T`, []string{`int`}, `[]int`}},
+		},
+
+		{`package dupltype0; type T[P interface{~int}] struct{ x P }; var x T[int]; var y T[int]`,
+			[]testInst{
+				{`T`, []string{`int`}, `struct{x int}`},
+				{`T`, []string{`int`}, `struct{x int}`},
+			},
+		},
+		{`package dupltype1; type T[P ~int] struct{ x P }; func (r *T[Q]) add(z T[Q]) { r.x += z.x }`,
+			[]testInst{
+				{`T`, []string{`Q`}, `struct{x Q}`},
+				{`T`, []string{`Q`}, `struct{x Q}`},
+			},
+		},
+		{`package dupltype1; import "lib"; var x lib.T[int]; var y lib.T[int]; var z lib.T[string]`,
+			[]testInst{
+				{`T`, []string{`int`}, `[]int`},
+				{`T`, []string{`int`}, `[]int`},
+				{`T`, []string{`string`}, `[]string`},
+			},
 		},
 	}
 
 	for _, test := range tests {
-		const lib = `package generic_lib
-
-func F[P any](P) {}
-
-type T[P any] []P
-`
-
 		imports := make(testImporter)
 		conf := Config{Importer: imports}
-		instances := make(map[*syntax.Name]Instance)
-		uses := make(map[*syntax.Name]Object)
+		instMap := make(map[*syntax.Name]Instance)
+		useMap := make(map[*syntax.Name]Object)
 		makePkg := func(src string) *Package {
 			f, err := parseSrc("p.go", src)
 			if err != nil {
 				t.Fatal(err)
 			}
-			pkg, err := conf.Check("", []*syntax.File{f}, &Info{Instances: instances, Uses: uses})
+			pkg, err := conf.Check("", []*syntax.File{f}, &Info{Instances: instMap, Uses: useMap})
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -574,60 +583,72 @@ type T[P any] []P
 		makePkg(lib)
 		pkg := makePkg(test.src)
 
-		// look for instance information
-		var targs []Type
-		var typ Type
-		for ident, inst := range instances {
-			if syntax.String(ident) == test.name {
-				for i := 0; i < inst.TypeArgs.Len(); i++ {
-					targs = append(targs, inst.TypeArgs.At(i))
-				}
-				typ = inst.Type
+		t.Run(pkg.Name(), func(t *testing.T) {
+			// Sort instances in source order for stability.
+			instances := sortedInstances(instMap)
+			if got, want := len(instances), len(test.instances); got != want {
+				t.Fatalf("got %d instances, want %d", got, want)
+			}
 
-				// Check that we can find the corresponding parameterized type.
-				ptype := uses[ident].Type()
+			// Pairwise compare with the expected instances.
+			for ii, inst := range instances {
+				var targs []Type
+				for i := 0; i < inst.Inst.TypeArgs.Len(); i++ {
+					targs = append(targs, inst.Inst.TypeArgs.At(i))
+				}
+				typ := inst.Inst.Type
+
+				testInst := test.instances[ii]
+				if got := inst.Name.Value; got != testInst.name {
+					t.Fatalf("got name %s, want %s", got, testInst.name)
+				}
+
+				if len(targs) != len(testInst.targs) {
+					t.Fatalf("got %d type arguments; want %d", len(targs), len(testInst.targs))
+				}
+				for i, targ := range targs {
+					if got := targ.String(); got != testInst.targs[i] {
+						t.Errorf("type argument %d: got %s; want %s", i, got, testInst.targs[i])
+					}
+				}
+				if got := typ.Underlying().String(); got != testInst.typ {
+					t.Errorf("package %s: got %s; want %s", pkg.Name(), got, testInst.typ)
+				}
+
+				// Verify the invariant that re-instantiating the corresponding generic
+				// type with TypeArgs results in an identical instance.
+				ptype := useMap[inst.Name].Type()
 				lister, _ := ptype.(interface{ TypeParams() *TypeParamList })
 				if lister == nil || lister.TypeParams().Len() == 0 {
-					t.Errorf("package %s: info.Types[%v] = %v, want parameterized type", pkg.Name(), ident, ptype)
-					continue
+					t.Fatalf("info.Types[%v] = %v, want parameterized type", inst.Name, ptype)
 				}
-
-				// Verify the invariant that re-instantiating the generic type with
-				// TypeArgs results in an equivalent type.
 				inst2, err := Instantiate(nil, ptype, targs, true)
 				if err != nil {
 					t.Errorf("Instantiate(%v, %v) failed: %v", ptype, targs, err)
 				}
-				if !Identical(inst.Type, inst2) {
-					t.Errorf("%v and %v are not identical", inst.Type, inst2)
+				if !Identical(inst.Inst.Type, inst2) {
+					t.Errorf("%v and %v are not identical", inst.Inst.Type, inst2)
 				}
-				break
 			}
-		}
-		if targs == nil {
-			t.Errorf("package %s: no instance information found for %s", pkg.Name(), test.name)
-			continue
-		}
-
-		// check that type arguments are correct
-		if len(targs) != len(test.targs) {
-			t.Errorf("package %s: got %d type arguments; want %d", pkg.Name(), len(targs), len(test.targs))
-			continue
-		}
-		for i, targ := range targs {
-			if got := targ.String(); got != test.targs[i] {
-				t.Errorf("package %s, %d. type argument: got %s; want %s", pkg.Name(), i, got, test.targs[i])
-				continue
-			}
-		}
-
-		// check that the types match
-		if got := typ.Underlying().String(); got != test.typ {
-			t.Errorf("package %s: got %s; want %s", pkg.Name(), got, test.typ)
-		}
+		})
 	}
 }
 
+type recordedInstance struct {
+	Name *syntax.Name
+	Inst Instance
+}
+
+func sortedInstances(m map[*syntax.Name]Instance) (instances []recordedInstance) {
+	for id, inst := range m {
+		instances = append(instances, recordedInstance{id, inst})
+	}
+	sort.Slice(instances, func(i, j int) bool {
+		return instances[i].Name.Pos().Cmp(instances[j].Name.Pos()) < 0
+	})
+	return instances
+}
+
 func TestDefsInfo(t *testing.T) {
 	var tests = []struct {
 		src  string
@@ -1598,19 +1619,41 @@ func TestLookupFieldOrMethod(t *testing.T) {
 		{"var x T; type T struct{ f int }", true, []int{0}, false},
 		{"var x T; type T struct{ a, b, f, c int }", true, []int{2}, false},
 
+		// field lookups on a generic type
+		{"var x T[int]; type T[P any] struct{}", false, nil, false},
+		{"var x T[int]; type T[P any] struct{ f P }", true, []int{0}, false},
+		{"var x T[int]; type T[P any] struct{ a, b, f, c P }", true, []int{2}, false},
+
 		// method lookups
 		{"var a T; type T struct{}; func (T) f() {}", true, []int{0}, false},
 		{"var a *T; type T struct{}; func (T) f() {}", true, []int{0}, true},
 		{"var a T; type T struct{}; func (*T) f() {}", true, []int{0}, false},
 		{"var a *T; type T struct{}; func (*T) f() {}", true, []int{0}, true}, // TODO(gri) should this report indirect = false?
 
+		// method lookups on a generic type
+		{"var a T[int]; type T[P any] struct{}; func (T[P]) f() {}", true, []int{0}, false},
+		{"var a *T[int]; type T[P any] struct{}; func (T[P]) f() {}", true, []int{0}, true},
+		{"var a T[int]; type T[P any] struct{}; func (*T[P]) f() {}", true, []int{0}, false},
+		{"var a *T[int]; type T[P any] struct{}; func (*T[P]) f() {}", true, []int{0}, true}, // TODO(gri) should this report indirect = false?
+
 		// collisions
 		{"type ( E1 struct{ f int }; E2 struct{ f int }; x struct{ E1; *E2 })", false, []int{1, 0}, false},
 		{"type ( E1 struct{ f int }; E2 struct{}; x struct{ E1; *E2 }); func (E2) f() {}", false, []int{1, 0}, false},
 
+		// collisions on a generic type
+		{"type ( E1[P any] struct{ f P }; E2[P any] struct{ f P }; x struct{ E1[int]; *E2[int] })", false, []int{1, 0}, false},
+		{"type ( E1[P any] struct{ f P }; E2[P any] struct{}; x struct{ E1[int]; *E2[int] }); func (E2[P]) f() {}", false, []int{1, 0}, false},
+
 		// outside methodset
 		// (*T).f method exists, but value of type T is not addressable
 		{"var x T; type T struct{}; func (*T) f() {}", false, nil, true},
+
+		// outside method set of a generic type
+		{"var x T[int]; type T[P any] struct{}; func (*T[P]) f() {}", false, nil, true},
+
+		// recursive generic types; see golang/go#52715
+		{"var a T[int]; type ( T[P any] struct { *N[P] }; N[P any] struct { *T[P] } ); func (N[P]) f() {}", true, []int{0, 0}, true},
+		{"var a T[int]; type ( T[P any] struct { *N[P] }; N[P any] struct { *T[P] } ); func (T[P]) f() {}", true, []int{0}, false},
 	}
 
 	for _, test := range tests {
@@ -1645,6 +1688,37 @@ func TestLookupFieldOrMethod(t *testing.T) {
 	}
 }
 
+// Test for golang/go#52715
+func TestLookupFieldOrMethod_RecursiveGeneric(t *testing.T) {
+	const src = `
+package pkg
+
+type Tree[T any] struct {
+	*Node[T]
+}
+
+func (*Tree[R]) N(r R) R { return r }
+
+type Node[T any] struct {
+	*Tree[T]
+}
+
+type Instance = *Tree[int]
+`
+
+	f, err := parseSrc("foo.go", src)
+	if err != nil {
+		panic(err)
+	}
+	pkg := NewPackage("pkg", f.PkgName.Value)
+	if err := NewChecker(nil, pkg, nil).Files([]*syntax.File{f}); err != nil {
+		panic(err)
+	}
+
+	T := pkg.Scope().Lookup("Instance").Type()
+	_, _, _ = LookupFieldOrMethod(T, false, pkg, "M") // verify that LookupFieldOrMethod terminates
+}
+
 func sameSlice(a, b []int) bool {
 	if len(a) != len(b) {
 		return false
@@ -1697,7 +1771,7 @@ func F(){
 	var F = /*F=func:12*/ F /*F=var:17*/ ; _ = F
 
 	var a []int
-	for i, x := range /*i=undef*/ /*x=var:16*/ a /*i=var:20*/ /*x=var:20*/ { _ = i; _ = x }
+	for i, x := range a /*i=undef*/ /*x=var:16*/ { _ = i; _ = x }
 
 	var i interface{}
 	switch y := i.(type) { /*y=undef*/
@@ -2267,6 +2341,103 @@ func TestInstanceIdentity(t *testing.T) {
 	}
 }
 
+// TestInstantiatedObjects verifies properties of instantiated objects.
+func TestInstantiatedObjects(t *testing.T) {
+	const src = `
+package p
+
+type T[P any] struct {
+	field P
+}
+
+func (recv *T[Q]) concreteMethod() {}
+
+type FT[P any] func(ftp P) (ftrp P)
+
+func F[P any](fp P) (frp P){ return }
+
+type I[P any] interface {
+	interfaceMethod(P)
+}
+
+var (
+	t T[int]
+	ft FT[int]
+	f = F[int]
+	i I[int]
+)
+`
+	info := &Info{
+		Defs: make(map[*syntax.Name]Object),
+	}
+	f, err := parseSrc("p.go", src)
+	if err != nil {
+		t.Fatal(err)
+	}
+	conf := Config{}
+	pkg, err := conf.Check(f.PkgName.Value, []*syntax.File{f}, info)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	lookup := func(name string) Type { return pkg.Scope().Lookup(name).Type() }
+	tests := []struct {
+		ident string
+		obj   Object
+	}{
+		{"field", lookup("t").Underlying().(*Struct).Field(0)},
+		{"concreteMethod", lookup("t").(*Named).Method(0)},
+		{"recv", lookup("t").(*Named).Method(0).Type().(*Signature).Recv()},
+		{"ftp", lookup("ft").Underlying().(*Signature).Params().At(0)},
+		{"ftrp", lookup("ft").Underlying().(*Signature).Results().At(0)},
+		{"fp", lookup("f").(*Signature).Params().At(0)},
+		{"frp", lookup("f").(*Signature).Results().At(0)},
+		{"interfaceMethod", lookup("i").Underlying().(*Interface).Method(0)},
+	}
+
+	// Collect all identifiers by name.
+	idents := make(map[string][]*syntax.Name)
+	syntax.Inspect(f, func(n syntax.Node) bool {
+		if id, ok := n.(*syntax.Name); ok {
+			idents[id.Value] = append(idents[id.Value], id)
+		}
+		return true
+	})
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.ident, func(t *testing.T) {
+			if got := len(idents[test.ident]); got != 1 {
+				t.Fatalf("found %d identifiers named %s, want 1", got, test.ident)
+			}
+			ident := idents[test.ident][0]
+			def := info.Defs[ident]
+			if def == test.obj {
+				t.Fatalf("info.Defs[%s] contains the test object", test.ident)
+			}
+			if def.Pkg() != test.obj.Pkg() {
+				t.Errorf("Pkg() = %v, want %v", def.Pkg(), test.obj.Pkg())
+			}
+			if def.Name() != test.obj.Name() {
+				t.Errorf("Name() = %v, want %v", def.Name(), test.obj.Name())
+			}
+			if def.Pos() != test.obj.Pos() {
+				t.Errorf("Pos() = %v, want %v", def.Pos(), test.obj.Pos())
+			}
+			if def.Parent() != test.obj.Parent() {
+				t.Fatalf("Parent() = %v, want %v", def.Parent(), test.obj.Parent())
+			}
+			if def.Exported() != test.obj.Exported() {
+				t.Fatalf("Exported() = %v, want %v", def.Exported(), test.obj.Exported())
+			}
+			if def.Id() != test.obj.Id() {
+				t.Fatalf("Id() = %v, want %v", def.Id(), test.obj.Id())
+			}
+			// String and Type are expected to differ.
+		})
+	}
+}
+
 func TestImplements(t *testing.T) {
 	const src = `
 package p

src/cmd/compile/internal/types2/call.go

@@ -423,7 +423,7 @@ var cgoPrefixes = [...]string{
 	"_Cmacro_", // function to evaluate the expanded expression
 }
 
-func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
+func (check *Checker) selector(x *operand, e *syntax.SelectorExpr, def *Named) {
 	// these must be declared before the "goto Error" statements
 	var (
 		obj      Object
@@ -526,6 +526,12 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 
 	check.exprOrType(x, e.X, false)
 	switch x.mode {
+	case typexpr:
+		// don't crash for "type T T.x" (was issue #51509)
+		if def != nil && x.typ == def {
+			check.cycleError([]Object{def.obj})
+			goto Error
+		}
 	case builtin:
 		check.errorf(e.Pos(), "cannot select on %s", x)
 		goto Error

src/cmd/compile/internal/types2/context.go

@@ -12,11 +12,12 @@ import (
 	"sync"
 )
 
-// An Context is an opaque type checking context. It may be used to share
+// A Context is an opaque type checking context. It may be used to share
 // identical type instances across type-checked packages or calls to
-// Instantiate.
+// Instantiate. Contexts are safe for concurrent use.
 //
-// It is safe for concurrent use.
+// The use of a shared context does not guarantee that identical instances are
+// deduplicated in all cases.
 type Context struct {
 	mu        sync.Mutex
 	typeMap   map[string][]ctxtEntry // type hash -> instances entries

src/cmd/compile/internal/types2/decl.go

@@ -636,14 +636,12 @@ func (check *Checker) collectMethods(obj *TypeName) {
 	base, _ := obj.typ.(*Named) // shouldn't fail but be conservative
 	if base != nil {
 		assert(base.targs.Len() == 0) // collectMethods should not be called on an instantiated type
-		u := base.under()
-		if t, _ := u.(*Struct); t != nil {
-			for _, fld := range t.fields {
-				if fld.name != "_" {
-					assert(mset.insert(fld) == nil)
-				}
-			}
-		}
+
+		// See issue #52529: we must delay the expansion of underlying here, as
+		// base may not be fully set-up.
+		check.later(func() {
+			check.checkFieldUniqueness(base)
+		}).describef(obj, "verifying field uniqueness for %v", base)
 
 		// Checker.Files may be called multiple times; additional package files
 		// may add methods to already type-checked types. Add pre-existing methods
@@ -662,17 +660,10 @@ func (check *Checker) collectMethods(obj *TypeName) {
 		assert(m.name != "_")
 		if alt := mset.insert(m); alt != nil {
 			var err error_
-			switch alt.(type) {
-			case *Var:
-				err.errorf(m.pos, "field and method with the same name %s", m.name)
-			case *Func:
-				if check.conf.CompilerErrorMessages {
-					err.errorf(m.pos, "%s.%s redeclared in this block", obj.Name(), m.name)
-				} else {
-					err.errorf(m.pos, "method %s already declared for %s", m.name, obj)
-				}
-			default:
-				unreachable()
+			if check.conf.CompilerErrorMessages {
+				err.errorf(m.pos, "%s.%s redeclared in this block", obj.Name(), m.name)
+			} else {
+				err.errorf(m.pos, "method %s already declared for %s", m.name, obj)
 			}
 			err.recordAltDecl(alt)
 			check.report(&err)
@@ -686,6 +677,36 @@ func (check *Checker) collectMethods(obj *TypeName) {
 	}
 }
 
+func (check *Checker) checkFieldUniqueness(base *Named) {
+	if t, _ := base.under().(*Struct); t != nil {
+		var mset objset
+		for i := 0; i < base.methods.Len(); i++ {
+			m := base.methods.At(i, nil)
+			assert(m.name != "_")
+			assert(mset.insert(m) == nil)
+		}
+
+		// Check that any non-blank field names of base are distinct from its
+		// method names.
+		for _, fld := range t.fields {
+			if fld.name != "_" {
+				if alt := mset.insert(fld); alt != nil {
+					// Struct fields should already be unique, so we should only
+					// encounter an alternate via collision with a method name.
+					_ = alt.(*Func)
+
+					// For historical consistency, we report the primary error on the
+					// method, and the alt decl on the field.
+					var err error_
+					err.errorf(alt, "field and method with the same name %s", fld.name)
+					err.recordAltDecl(fld)
+					check.report(&err)
+				}
+			}
+		}
+	}
+}
+
 func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
 	assert(obj.typ == nil)
 
@@ -735,7 +756,7 @@ func (check *Checker) declStmt(list []syntax.Decl) {
 			top := len(check.delayed)
 
 			// iota is the index of the current constDecl within the group
-			if first < 0 || list[index-1].(*syntax.ConstDecl).Group != s.Group {
+			if first < 0 || s.Group == nil || list[index-1].(*syntax.ConstDecl).Group != s.Group {
 				first = index
 				last = nil
 			}

src/cmd/compile/internal/types2/expr.go

@@ -1556,7 +1556,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
 		return kind
 
 	case *syntax.SelectorExpr:
-		check.selector(x, e)
+		check.selector(x, e, nil)
 
 	case *syntax.IndexExpr:
 		if check.indexExpr(x, e) {
@@ -1642,6 +1642,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
 				case invalid:
 					goto Error
 				case typexpr:
+					check.validVarType(e.X, x.typ)
 					x.typ = &Pointer{base: x.typ}
 				default:
 					var base Type

src/cmd/compile/internal/types2/infer.go

@@ -488,21 +488,88 @@ func (check *Checker) inferB(pos syntax.Pos, tparams []*TypeParam, targs []Type)
 		}
 	}
 
-	// If a constraint has a core type, unify the corresponding type parameter with it.
-	for _, tpar := range tparams {
-		if ctype := adjCoreType(tpar); ctype != nil {
-			if !u.unify(tpar, ctype) {
-				// TODO(gri) improve error message by providing the type arguments
-				//           which we know already
-				check.errorf(pos, "%s does not match %s", tpar, ctype)
-				return nil, 0
+	// Repeatedly apply constraint type inference as long as
+	// there are still unknown type arguments and progress is
+	// being made.
+	//
+	// This is an O(n^2) algorithm where n is the number of
+	// type parameters: if there is progress (and iteration
+	// continues), at least one type argument is inferred
+	// per iteration and we have a doubly nested loop.
+	// In practice this is not a problem because the number
+	// of type parameters tends to be very small (< 5 or so).
+	// (It should be possible for unification to efficiently
+	// signal newly inferred type arguments; then the loops
+	// here could handle the respective type parameters only,
+	// but that will come at a cost of extra complexity which
+	// may not be worth it.)
+	for n := u.x.unknowns(); n > 0; {
+		nn := n
+
+		for i, tpar := range tparams {
+			// If there is a core term (i.e., a core type with tilde information)
+			// unify the type parameter with the core type.
+			if core, single := coreTerm(tpar); core != nil {
+				// A type parameter can be unified with its core type in two cases.
+				tx := u.x.at(i)
+				switch {
+				case tx != nil:
+					// The corresponding type argument tx is known.
+					// In this case, if the core type has a tilde, the type argument's underlying
+					// type must match the core type, otherwise the type argument and the core type
+					// must match.
+					// If tx is an external type parameter, don't consider its underlying type
+					// (which is an interface). Core type unification will attempt to unify against
+					// core.typ.
+					// Note also that even with inexact unification we cannot leave away the under
+					// call here because it's possible that both tx and core.typ are named types,
+					// with under(tx) being a (named) basic type matching core.typ. Such cases do
+					// not match with inexact unification.
+					if core.tilde && !isTypeParam(tx) {
+						tx = under(tx)
+					}
+					if !u.unify(tx, core.typ) {
+						// TODO(gri) improve error message by providing the type arguments
+						//           which we know already
+						// Don't use term.String() as it always qualifies types, even if they
+						// are in the current package.
+						tilde := ""
+						if core.tilde {
+							tilde = "~"
+						}
+						check.errorf(pos, "%s does not match %s%s", tpar, tilde, core.typ)
+						return nil, 0
+					}
+
+				case single && !core.tilde:
+					// The corresponding type argument tx is unknown and there's a single
+					// specific type and no tilde.
+					// In this case the type argument must be that single type; set it.
+					u.x.set(i, core.typ)
+
+				default:
+					// Unification is not possible and no progress was made.
+					continue
+				}
+
+				// The number of known type arguments may have changed.
+				nn = u.x.unknowns()
+				if nn == 0 {
+					break // all type arguments are known
+				}
 			}
 		}
+
+		assert(nn <= n)
+		if nn == n {
+			break // no progress
+		}
+		n = nn
 	}
 
 	// u.x.types() now contains the incoming type arguments plus any additional type
-	// arguments which were inferred from core types. The newly inferred non-
-	// nil entries may still contain references to other type parameters.
+	// arguments which were inferred from core terms. The newly inferred non-nil
+	// entries may still contain references to other type parameters.
 	// For instance, for [A any, B interface{ []C }, C interface{ *A }], if A == int
 	// was given, unification produced the type list [int, []C, *A]. We eliminate the
 	// remaining type parameters by substituting the type parameters in this type list
@@ -591,26 +658,40 @@ func (check *Checker) inferB(pos syntax.Pos, tparams []*TypeParam, targs []Type)
 	return
 }
 
-// adjCoreType returns the core type of tpar unless the
-// type parameter embeds a single, possibly named type,
-// in which case it returns that single type instead.
-// (The core type is always the underlying type of that
-// single type.)
-func adjCoreType(tpar *TypeParam) Type {
-	var single *term
-	if tpar.is(func(t *term) bool {
-		if single == nil && t != nil {
-			single = t
-			return true
+// If the type parameter has a single specific type S, coreTerm returns (S, true).
+// Otherwise, if tpar has a core type T, it returns a term corresponding to that
+// core type and false. In that case, if any term of tpar has a tilde, the core
+// term has a tilde. In all other cases coreTerm returns (nil, false).
+func coreTerm(tpar *TypeParam) (*term, bool) {
+	n := 0
+	var single *term // valid if n == 1
+	var tilde bool
+	tpar.is(func(t *term) bool {
+		if t == nil {
+			assert(n == 0)
+			return false // no terms
 		}
-		return false // zero or more than one terms
-	}) {
+		n++
+		single = t
+		if t.tilde {
+			tilde = true
+		}
+		return true
+	})
+	if n == 1 {
 		if debug {
-			assert(under(single.typ) == coreType(tpar))
+			assert(debug && under(single.typ) == coreType(tpar))
 		}
-		return single.typ
+		return single, true
 	}
-	return coreType(tpar)
+	if typ := coreType(tpar); typ != nil {
+		// A core type is always an underlying type.
+		// If any term of tpar has a tilde, we don't
+		// have a precise core type and we must return
+		// a tilde as well.
+		return &term{tilde, typ}, false
+	}
+	return nil, false
 }
 
 type cycleFinder struct {
@@ -658,8 +739,6 @@ func (w *cycleFinder) typ(typ Type) {
 	//      in signatures where they are handled explicitly.
 
 	case *Signature:
-		// There are no "method types" so we should never see a recv.
-		assert(t.recv == nil)
 		if t.params != nil {
 			w.varList(t.params.vars)
 		}

src/cmd/compile/internal/types2/instantiate.go

@@ -15,16 +15,17 @@ import (
 
 // Instantiate instantiates the type orig with the given type arguments targs.
 // orig must be a *Named or a *Signature type. If there is no error, the
-// resulting Type is a new, instantiated (not parameterized) type of the same
-// kind (either a *Named or a *Signature). Methods attached to a *Named type
-// are also instantiated, and associated with a new *Func that has the same
-// position as the original method, but nil function scope.
+// resulting Type is an instantiated type of the same kind (either a *Named or
+// a *Signature). Methods attached to a *Named type are also instantiated, and
+// associated with a new *Func that has the same position as the original
+// method, but nil function scope.
 //
 // If ctxt is non-nil, it may be used to de-duplicate the instance against
 // previous instances with the same identity. As a special case, generic
 // *Signature origin types are only considered identical if they are pointer
 // equivalent, so that instantiating distinct (but possibly identical)
-// signatures will yield different instances.
+// signatures will yield different instances. The use of a shared context does
+// not guarantee that identical instances are deduplicated in all cases.
 //
 // If validate is set, Instantiate verifies that the number of type arguments
 // and parameters match, and that the type arguments satisfy their

src/cmd/compile/internal/types2/lookup.go

@@ -25,9 +25,9 @@ import (
 // The last index entry is the field or method index in the (possibly embedded)
 // type where the entry was found, either:
 //
-//	1) the list of declared methods of a named type; or
-//	2) the list of all methods (method set) of an interface type; or
-//	3) the list of fields of a struct type.
+//  1. the list of declared methods of a named type; or
+//  2. the list of all methods (method set) of an interface type; or
+//  3. the list of fields of a struct type.
 //
 // The earlier index entries are the indices of the embedded struct fields
 // traversed to get to the found entry, starting at depth 0.
@@ -35,13 +35,12 @@ import (
 // If no entry is found, a nil object is returned. In this case, the returned
 // index and indirect values have the following meaning:
 //
-//	- If index != nil, the index sequence points to an ambiguous entry
-//	(the same name appeared more than once at the same embedding level).
-//
-//	- If indirect is set, a method with a pointer receiver type was found
-//      but there was no pointer on the path from the actual receiver type to
-//	the method's formal receiver base type, nor was the receiver addressable.
+//   - If index != nil, the index sequence points to an ambiguous entry
+//     (the same name appeared more than once at the same embedding level).
 //
+//   - If indirect is set, a method with a pointer receiver type was found
+//     but there was no pointer on the path from the actual receiver type to
+//     the method's formal receiver base type, nor was the receiver addressable.
 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
 	if T == nil {
 		panic("LookupFieldOrMethod on nil type")
@@ -70,7 +69,8 @@ func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (o
 	// see if there is a matching field (but not a method, those need to be declared
 	// explicitly in the constraint). If the constraint is a named pointer type (see
 	// above), we are ok here because only fields are accepted as results.
-	if obj == nil && isTypeParam(T) {
+	const enableTParamFieldLookup = false // see issue #51576
+	if enableTParamFieldLookup && obj == nil && isTypeParam(T) {
 		if t := coreType(T); t != nil {
 			obj, index, indirect = lookupFieldOrMethod(t, addressable, pkg, name, false)
 			if _, ok := obj.(*Var); !ok {
@@ -81,11 +81,6 @@ func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (o
 	return
 }
 
-// TODO(gri) The named type consolidation and seen maps below must be
-//           indexed by unique keys for a given type. Verify that named
-//           types always have only one representation (even when imported
-//           indirectly via different packages.)
-
 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
 // If foldCase is true, the lookup for methods will include looking for any method
 // which case-folds to the same as 'name' (used for giving helpful error messages).
@@ -110,14 +105,12 @@ func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, fo
 	// Start with typ as single entry at shallowest depth.
 	current := []embeddedType{{typ, nil, isPtr, false}}
 
-	// Named types that we have seen already, allocated lazily.
+	// seen tracks named types that we have seen already, allocated lazily.
 	// Used to avoid endless searches in case of recursive types.
-	// Since only Named types can be used for recursive types, we
-	// only need to track those.
-	// (If we ever allow type aliases to construct recursive types,
-	// we must use type identity rather than pointer equality for
-	// the map key comparison, as we do in consolidateMultiples.)
-	var seen map[*Named]bool
+	//
+	// We must use a lookup on identity rather than a simple map[*Named]bool as
+	// instantiated types may be identical but not equal.
+	var seen instanceLookup
 
 	// search current depth
 	for len(current) > 0 {
@@ -130,7 +123,7 @@ func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, fo
 			// If we have a named type, we may have associated methods.
 			// Look for those first.
 			if named, _ := typ.(*Named); named != nil {
-				if seen[named] {
+				if alt := seen.lookup(named); alt != nil {
 					// We have seen this type before, at a more shallow depth
 					// (note that multiples of this type at the current depth
 					// were consolidated before). The type at that depth shadows
@@ -138,10 +131,7 @@ func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string, fo
 					// this one.
 					continue
 				}
-				if seen == nil {
-					seen = make(map[*Named]bool)
-				}
-				seen[named] = true
+				seen.add(named)
 
 				// look for a matching attached method
 				named.resolve(nil)
@@ -271,6 +261,27 @@ func lookupType(m map[Type]int, typ Type) (int, bool) {
 	return 0, false
 }
 
+type instanceLookup struct {
+	m map[*Named][]*Named
+}
+
+func (l *instanceLookup) lookup(inst *Named) *Named {
+	for _, t := range l.m[inst.Origin()] {
+		if Identical(inst, t) {
+			return t
+		}
+	}
+	return nil
+}
+
+func (l *instanceLookup) add(inst *Named) {
+	if l.m == nil {
+		l.m = make(map[*Named][]*Named)
+	}
+	insts := l.m[inst.Origin()]
+	l.m[inst.Origin()] = append(insts, inst)
+}
+
 // MissingMethod returns (nil, false) if V implements T, otherwise it
 // returns a missing method required by T and whether it is missing or
 // just has the wrong type.
@@ -280,7 +291,6 @@ func lookupType(m map[Type]int, typ Type) (int, bool) {
 // is not set), MissingMethod only checks that methods of T which are also
 // present in V have matching types (e.g., for a type assertion x.(T) where
 // x is of interface type V).
-//
 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
 	m, alt := (*Checker)(nil).missingMethod(V, T, static)
 	// Only report a wrong type if the alternative method has the same name as m.

src/cmd/compile/internal/types2/named.go

@@ -98,10 +98,10 @@ func (t *Named) cleanup() {
 }
 
 // Obj returns the type name for the declaration defining the named type t. For
-// instantiated types, this is the type name of the base type.
+// instantiated types, this is same as the type name of the origin type.
 func (t *Named) Obj() *TypeName { return t.orig.obj } // for non-instances this is the same as t.obj
 
-// Origin returns the parameterized type from which the named type t is
+// Origin returns the generic type from which the named type t is
 // instantiated. If t is not an instantiated type, the result is t.
 func (t *Named) Origin() *Named { return t.orig }
 
@@ -109,7 +109,7 @@ func (t *Named) Origin() *Named { return t.orig }
 //           between parameterized instantiated and non-instantiated types.
 
 // TypeParams returns the type parameters of the named type t, or nil.
-// The result is non-nil for an (originally) parameterized type even if it is instantiated.
+// The result is non-nil for an (originally) generic type even if it is instantiated.
 func (t *Named) TypeParams() *TypeParamList { return t.resolve(nil).tparams }
 
 // SetTypeParams sets the type parameters of the named type t.
@@ -122,7 +122,11 @@ func (t *Named) SetTypeParams(tparams []*TypeParam) {
 // TypeArgs returns the type arguments used to instantiate the named type t.
 func (t *Named) TypeArgs() *TypeList { return t.targs }
 
-// NumMethods returns the number of explicit methods whose receiver is named type t.
+// NumMethods returns the number of explicit methods defined for t.
+//
+// For an ordinary or instantiated type t, the receiver base type of these
+// methods will be the named type t. For an uninstantiated generic type t, each
+// method receiver will be instantiated with its receiver type parameters.
 func (t *Named) NumMethods() int { return t.resolve(nil).methods.Len() }
 
 // Method returns the i'th method of named type t for 0 <= i < t.NumMethods().
@@ -186,7 +190,7 @@ func (t *Named) instantiateMethod(i int) *Func {
 		rtyp = t
 	}
 
-	sig.recv = NewParam(origSig.recv.pos, origSig.recv.pkg, origSig.recv.name, rtyp)
+	sig.recv = substVar(origSig.recv, rtyp)
 	return NewFunc(origm.pos, origm.pkg, origm.name, sig)
 }
 

src/cmd/compile/internal/types2/resolver.go

@@ -339,7 +339,7 @@ func (check *Checker) collectObjects() {
 
 			case *syntax.ConstDecl:
 				// iota is the index of the current constDecl within the group
-				if first < 0 || file.DeclList[index-1].(*syntax.ConstDecl).Group != s.Group {
+				if first < 0 || s.Group == nil || file.DeclList[index-1].(*syntax.ConstDecl).Group != s.Group {
 					first = index
 					last = nil
 				}
@@ -413,7 +413,7 @@ func (check *Checker) collectObjects() {
 
 			case *syntax.TypeDecl:
 				if len(s.TParamList) != 0 && !check.allowVersion(pkg, 1, 18) {
-					check.softErrorf(s.TParamList[0], "type parameters require go1.18 or later")
+					check.versionErrorf(s.TParamList[0], "go1.18", "type parameter")
 				}
 				obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Value, nil)
 				check.declarePkgObj(s.Name, obj, &declInfo{file: fileScope, tdecl: s})
@@ -458,7 +458,7 @@ func (check *Checker) collectObjects() {
 					check.recordDef(s.Name, obj)
 				}
 				if len(s.TParamList) != 0 && !check.allowVersion(pkg, 1, 18) && !hasTParamError {
-					check.softErrorf(s.TParamList[0], "type parameters require go1.18 or later")
+					check.versionErrorf(s.TParamList[0], "go1.18", "type parameter")
 				}
 				info := &declInfo{file: fileScope, fdecl: s}
 				// Methods are not package-level objects but we still track them in the

src/cmd/compile/internal/types2/stmt.go

@@ -626,14 +626,15 @@ func (check *Checker) stmt(ctxt stmtContext, s syntax.Stmt) {
 
 	case *syntax.ForStmt:
 		inner |= breakOk | continueOk
-		check.openScope(s, "for")
-		defer check.closeScope()
 
 		if rclause, _ := s.Init.(*syntax.RangeClause); rclause != nil {
 			check.rangeStmt(inner, s, rclause)
 			break
 		}
 
+		check.openScope(s, "for")
+		defer check.closeScope()
+
 		check.simpleStmt(s.Init)
 		if s.Cond != nil {
 			var x operand
@@ -809,8 +810,6 @@ func (check *Checker) typeSwitchStmt(inner stmtContext, s *syntax.SwitchStmt, gu
 }
 
 func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *syntax.RangeClause) {
-	// scope already opened
-
 	// determine lhs, if any
 	sKey := rclause.Lhs // possibly nil
 	var sValue, sExtra syntax.Expr
@@ -866,6 +865,11 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 		}
 	}
 
+	// Open the for-statement block scope now, after the range clause.
+	// Iteration variables declared with := need to go in this scope (was issue #51437).
+	check.openScope(s, "range")
+	defer check.closeScope()
+
 	// check assignment to/declaration of iteration variables
 	// (irregular assignment, cannot easily map to existing assignment checks)
 
@@ -874,9 +878,7 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 	rhs := [2]Type{key, val} // key, val may be nil
 
 	if rclause.Def {
-		// short variable declaration; variable scope starts after the range clause
-		// (the for loop opens a new scope, so variables on the lhs never redeclare
-		// previously declared variables)
+		// short variable declaration
 		var vars []*Var
 		for i, lhs := range lhs {
 			if lhs == nil {
@@ -913,12 +915,8 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
 
 		// declare variables
 		if len(vars) > 0 {
-			scopePos := syntax.EndPos(rclause.X) // TODO(gri) should this just be s.Body.Pos (spec clarification)?
+			scopePos := s.Body.Pos()
 			for _, obj := range vars {
-				// spec: "The scope of a constant or variable identifier declared inside
-				// a function begins at the end of the ConstSpec or VarSpec (ShortVarDecl
-				// for short variable declarations) and ends at the end of the innermost
-				// containing block."
 				check.declare(check.scope, nil /* recordDef already called */, obj, scopePos)
 			}
 		} else {

src/cmd/compile/internal/types2/subst.go

@@ -290,14 +290,18 @@ func (subst *subster) typOrNil(typ Type) Type {
 func (subst *subster) var_(v *Var) *Var {
 	if v != nil {
 		if typ := subst.typ(v.typ); typ != v.typ {
-			copy := *v
-			copy.typ = typ
-			return &copy
+			return substVar(v, typ)
 		}
 	}
 	return v
 }
 
+func substVar(v *Var, typ Type) *Var {
+	copy := *v
+	copy.typ = typ
+	return &copy
+}
+
 func (subst *subster) tuple(t *Tuple) *Tuple {
 	if t != nil {
 		if vars, copied := subst.varList(t.vars); copied {
@@ -410,9 +414,8 @@ func replaceRecvType(in []*Func, old, new Type) (out []*Func, copied bool) {
 				copied = true
 			}
 			newsig := *sig
-			sig = &newsig
-			sig.recv = NewVar(sig.recv.pos, sig.recv.pkg, "", new)
-			out[i] = NewFunc(method.pos, method.pkg, method.name, sig)
+			newsig.recv = substVar(sig.recv, new)
+			out[i] = NewFunc(method.pos, method.pkg, method.name, &newsig)
 		}
 	}
 	return

src/cmd/compile/internal/types2/testdata/check/const0.src

@@ -349,6 +349,25 @@ const _ = unsafe.Sizeof(func() {
 	assert(iota == 0)
 })
 
+// issue #52438
+const i1 = iota
+const i2 = iota
+const i3 = iota
+
+func _() {
+	assert(i1 == 0)
+	assert(i2 == 0)
+	assert(i3 == 0)
+
+	const i4 = iota
+	const i5 = iota
+	const i6 = iota
+
+	assert(i4 == 0)
+	assert(i5 == 0)
+	assert(i6 == 0)
+}
+
 // untyped constants must not get arbitrarily large
 const prec = 512 // internal maximum precision for integers
 const maxInt = (1<<(prec/2) - 1) * (1<<(prec/2) + 1) // == 1<<prec - 1

src/cmd/compile/internal/types2/testdata/check/funcinference.go2

@@ -8,21 +8,21 @@ import "strconv"
 
 type any interface{}
 
-func f0[A any, B interface{~*C}, C interface{~*D}, D interface{~*A}](A, B, C, D) {}
+func f0[A any, B interface{*C}, C interface{*D}, D interface{*A}](A, B, C, D) {}
 func _() {
 	f := f0[string]
 	f("a", nil, nil, nil)
 	f0("a", nil, nil, nil)
 }
 
-func f1[A any, B interface{~*A}](A, B) {}
+func f1[A any, B interface{*A}](A, B) {}
 func _() {
 	f := f1[int]
 	f(int(0), new(int))
 	f1(int(0), new(int))
 }
 
-func f2[A any, B interface{~[]A}](A, B) {}
+func f2[A any, B interface{[]A}](A, B) {}
 func _() {
 	f := f2[byte]
 	f(byte(0), []byte{})
@@ -38,7 +38,7 @@ func _() {
 // 	f3(x, &x, &x)
 // }
 
-func f4[A any, B interface{~[]C}, C interface{~*A}](A, B, C) {}
+func f4[A any, B interface{[]C}, C interface{*A}](A, B, C) {}
 func _() {
 	f := f4[int]
 	var x int
@@ -46,7 +46,7 @@ func _() {
 	f4(x, []*int{}, &x)
 }
 
-func f5[A interface{~struct{b B; c C}}, B any, C interface{~*B}](x B) A { panic(0) }
+func f5[A interface{struct{b B; c C}}, B any, C interface{*B}](x B) A { panic(0) }
 func _() {
 	x := f5(1.2)
 	var _ float64 = x.b
@@ -79,14 +79,14 @@ var _ = Double(MySlice{1})
 
 type Setter[B any] interface {
 	Set(string)
-	~*B
+	*B
 }
 
 func FromStrings[T interface{}, PT Setter[T]](s []string) []T {
 	result := make([]T, len(s))
 	for i, v := range s {
 		// The type of &result[i] is *T which is in the type list
-		// of Setter2, so we can convert it to PT.
+		// of Setter, so we can convert it to PT.
 		p := PT(&result[i])
 		// PT has a Set method.
 		p.Set(v)

src/cmd/compile/internal/types2/testdata/check/typeinference.go2

@@ -4,44 +4,46 @@
 
 package typeInference
 
+// As of issue #51527, type-type inference has been disabled.
+
 // basic inference
 type Tb[P ~*Q, Q any] int
 func _() {
-	var x Tb[*int]
+	var x Tb /* ERROR got 1 arguments */ [*int]
 	var y Tb[*int, int]
-	x = y
+	x = y /* ERROR cannot use y .* in assignment */
 	_ = x
 }
 
 // recursive inference
-type Tr[A any, B ~*C, C ~*D, D ~*A] int
+type Tr[A any, B *C, C *D, D *A] int
 func _() {
-	var x Tr[string]
+	var x Tr /* ERROR got 1 arguments */ [string]
 	var y Tr[string, ***string, **string, *string]
 	var z Tr[int, ***int, **int, *int]
-	x = y
+	x = y /* ERROR cannot use y .* in assignment */
 	x = z // ERROR cannot use z .* as Tr
 	_ = x
 }
 
 // other patterns of inference
-type To0[A any, B ~[]A] int
-type To1[A any, B ~struct{a A}] int
-type To2[A any, B ~[][]A] int
-type To3[A any, B ~[3]*A] int
-type To4[A any, B any, C ~struct{a A; b B}] int
+type To0[A any, B []A] int
+type To1[A any, B struct{a A}] int
+type To2[A any, B [][]A] int
+type To3[A any, B [3]*A] int
+type To4[A any, B any, C struct{a A; b B}] int
 func _() {
-	var _ To0[int]
-	var _ To1[int]
-	var _ To2[int]
-	var _ To3[int]
-	var _ To4[int, string]
+	var _ To0 /* ERROR got 1 arguments */ [int]
+	var _ To1 /* ERROR got 1 arguments */ [int]
+	var _ To2 /* ERROR got 1 arguments */ [int]
+	var _ To3 /* ERROR got 1 arguments */ [int]
+	var _ To4 /* ERROR got 2 arguments */ [int, string]
 }
 
 // failed inference
 type Tf0[A, B any] int
 type Tf1[A any, B ~struct{a A; c C}, C any] int
 func _() {
-	var _ Tf0 /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [int]
-	var _ Tf1 /* ERROR cannot infer B */ /* ERROR got 1 arguments but 3 type parameters */ [int]
+	var _ Tf0 /* ERROR got 1 arguments but 2 type parameters */ [int]
+	var _ Tf1 /* ERROR got 1 arguments but 3 type parameters */ [int]
 }

src/cmd/compile/internal/types2/testdata/examples/constraints.go2

@@ -24,7 +24,8 @@ type (
 	_ interface{int|any}
 	_ interface{int|~string|union}
 	_ interface{int|~string|interface{int}}
-	_ interface{union|union /* ERROR overlapping terms p.union and p.union */ }
+	_ interface{union|int}   // interfaces (here: union) are ignored when checking for overlap
+	_ interface{union|union} // ditto
 
 	// For now we do not permit interfaces with methods in unions.
 	_ interface{~ /* ERROR invalid use of ~ */ any}

src/cmd/compile/internal/types2/testdata/examples/inference.go2

@@ -78,7 +78,7 @@ func _() {
 	related1(si, "foo" /* ERROR cannot use "foo" */ )
 }
 
-func related2[Elem any, Slice interface{~[]Elem}](e Elem, s Slice) {}
+func related2[Elem any, Slice interface{[]Elem}](e Elem, s Slice) {}
 
 func _() {
 	// related2 can be called with explicit instantiation.
@@ -109,16 +109,8 @@ func _() {
 	related3[int, []int]()
 	related3[byte, List[byte]]()
 
-	// Alternatively, the 2nd type argument can be inferred
-	// from the first one through constraint type inference.
-	related3[int]()
-
-	// The inferred type is the core type of the Slice
-	// type parameter.
-	var _ []int = related3[int]()
-
-	// It is not the defined parameterized type List.
-	type anotherList []float32
-	var _ anotherList = related3[float32]() // valid
-	var _ anotherList = related3 /* ERROR cannot use .* \(value of type List\[float32\]\) as anotherList */ [float32, List[float32]]()
+	// The 2nd type argument cannot be inferred from the first
+	// one because there's two possible choices: []Elem and
+	// List[Elem].
+	related3[int]( /* ERROR cannot infer Slice */ )
 }

src/cmd/compile/internal/types2/testdata/examples/typesets.go2

@@ -35,7 +35,7 @@ func _() int {
 	return deref(p)
 }
 
-func addrOfCopy[V any, P ~*V](v V) P {
+func addrOfCopy[V any, P *V](v V) P {
 	return &v
 }
 

src/cmd/compile/internal/types2/testdata/fixedbugs/issue41124.go2

@@ -47,7 +47,7 @@ type _ struct{
 }
 
 type _ struct{
-	I3 // ERROR interface is .* comparable
+	I3 // ERROR interface contains type constraints
 }
 
 // General composite types.
@@ -59,19 +59,19 @@ type (
 	_ []I1 // ERROR interface is .* comparable
 	_ []I2 // ERROR interface contains type constraints
 
-	_ *I3 // ERROR interface is .* comparable
+	_ *I3 // ERROR interface contains type constraints
 	_ map[I1 /* ERROR interface is .* comparable */ ]I2 // ERROR interface contains type constraints
-	_ chan I3 // ERROR interface is .* comparable
+	_ chan I3 // ERROR interface contains type constraints
 	_ func(I1 /* ERROR interface is .* comparable */ )
 	_ func() I2 // ERROR interface contains type constraints
 )
 
 // Other cases.
 
-var _ = [...]I3 /* ERROR interface is .* comparable */ {}
+var _ = [...]I3 /* ERROR interface contains type constraints */ {}
 
 func _(x interface{}) {
-	_ = x.(I3 /* ERROR interface is .* comparable */ )
+	_ = x.(I3 /* ERROR interface contains type constraints */ )
 }
 
 type T1[_ any] struct{}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue45548.go2

@@ -4,7 +4,7 @@
 
 package p
 
-func f[F interface{~*Q}, G interface{~*R}, Q, R any](q Q, r R) {}
+func f[F interface{*Q}, G interface{*R}, Q, R any](q Q, r R) {}
 
 func _() {
 	f[*float64, *int](1, 2)

src/cmd/compile/internal/types2/testdata/fixedbugs/issue47818.go2

@@ -8,13 +8,13 @@
 
 package go1_17
 
-type T[P /* ERROR type parameters require go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ] struct{}
+type T[P /* ERROR type parameter requires go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ] struct{}
 
 // for init (and main, but we're not in package main) we should only get one error
 func init[P /* ERROR func init must have no type parameters */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ]()   {}
-func main[P /* ERROR type parameters require go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ]() {}
+func main[P /* ERROR type parameter requires go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ]() {}
 
-func f[P /* ERROR type parameters require go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ](x P) {
+func f[P /* ERROR type parameter requires go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ](x P) {
 	var _ T[ /* ERROR type instantiation requires go1\.18 or later */ int]
 	var _ (T[ /* ERROR type instantiation requires go1\.18 or later */ int])
 	_ = T[ /* ERROR type instantiation requires go1\.18 or later */ int]{}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue49541.go2

@@ -10,9 +10,10 @@ type S[A, B any] struct {
 
 func (S[A, B]) m() {}
 
-// TODO(gri) We should only report one error below. See issue #50588.
+// TODO(gri): with type-type inference enabled we should only report one error
+// below. See issue #50588.
 
-func _[A any](s S /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [A]) {
+func _[A any](s S /* ERROR got 1 arguments but 2 type parameters */ [A]) {
 	// we should see no follow-on errors below
 	s.f = 1
 	s.m()
@@ -21,7 +22,7 @@ func _[A any](s S /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type
 // another test case from the issue
 
 func _() {
-	X(Interface[*F /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [string]](Impl{}))
+	X(Interface[*F /* ERROR got 1 arguments but 2 type parameters */ [string]](Impl{}))
 }
 
 func X[Q Qer](fs Interface[Q]) {

src/cmd/compile/internal/types2/testdata/fixedbugs/issue50417.go2

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Field accesses through type parameters are disabled
+// until we have a more thorough understanding of the
+// implications on the spec. See issue #51576.
+
 package p
 
 type Sf struct {
@@ -9,13 +13,13 @@ type Sf struct {
 }
 
 func f0[P Sf](p P) {
-        _ = p.f
-        p.f = 0
+        _ = p.f // ERROR p\.f undefined
+        p.f /* ERROR p\.f undefined */ = 0
 }
 
 func f0t[P ~struct{f int}](p P) {
-        _ = p.f
-        p.f = 0
+        _ = p.f // ERROR p\.f undefined
+        p.f /* ERROR p\.f undefined */ = 0
 }
 
 var _ = f0[Sf]
@@ -25,8 +29,8 @@ var _ = f0[Sm /* ERROR does not implement */ ]
 var _ = f0t[Sm /* ERROR does not implement */ ]
 
 func f1[P interface{ Sf; m() }](p P) {
-        _ = p.f
-        p.f = 0
+        _ = p.f // ERROR p\.f undefined
+        p.f /* ERROR p\.f undefined */ = 0
         p.m()
 }
 
@@ -44,8 +48,8 @@ type Sfm struct {
 func (Sfm) m() {}
 
 func f2[P interface{ Sfm; m() }](p P) {
-        _ = p.f
-        p.f = 0
+        _ = p.f // ERROR p\.f undefined
+        p.f /* ERROR p\.f undefined */ = 0
         p.m()
 }
 
@@ -56,8 +60,8 @@ var _ = f2[Sfm]
 type PSfm *Sfm
 
 func f3[P interface{ PSfm }](p P) {
-        _ = p.f
-        p.f = 0
+        _ = p.f // ERROR p\.f undefined
+        p.f /* ERROR p\.f undefined */ = 0
         p.m /* ERROR type P has no field or method m */ ()
 }
 

src/cmd/compile/internal/types2/testdata/fixedbugs/issue50782.go2

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Field accesses through type parameters are disabled
+// until we have a more thorough understanding of the
+// implications on the spec. See issue #51576.
+
 package p
 
 // The first example from the issue.
@@ -18,9 +22,12 @@ type numericAbs[T Numeric] interface {
 // AbsDifference computes the absolute value of the difference of
 // a and b, where the absolute value is determined by the Abs method.
 func absDifference[T numericAbs[T /* ERROR T does not implement Numeric */]](a, b T) T {
-	// TODO: the error below should probably be positioned on the '-'.
-	d := a /* ERROR "invalid operation: operator - not defined" */ .Value - b.Value
-	return d.Abs()
+	// Field accesses are not permitted for now. Keep an error so
+	// we can find and fix this code once the situation changes.
+	return a.Value // ERROR a\.Value undefined
+	// TODO: The error below should probably be positioned on the '-'.
+	// d := a /* ERROR "invalid operation: operator - not defined" */ .Value - b.Value
+	// return d.Abs()
 }
 
 // The second example from the issue.

src/cmd/compile/internal/types2/testdata/fixedbugs/issue50929.go2

@@ -16,7 +16,7 @@ func G[A, B any](F[A, B]) {
 
 func _() {
 	// TODO(gri) only report one error below (issue #50932)
-	var x F /* ERROR cannot infer B */ /* ERROR got 1 arguments but 2 type parameters */ [int]
+	var x F /* ERROR got 1 arguments but 2 type parameters */ [int]
 	G(x /* ERROR does not match */)
 }
 
@@ -46,9 +46,9 @@ func NSG[G any](c RSC[G]) {
 	fmt.Println(c)
 }
 
-func MMD[Rc RC /* ERROR cannot infer RG */ /* ERROR got 1 arguments */ [RG], RG any, G any]() M /* ERROR got 2 arguments */ /* ERROR Rc does not match */ [Rc, RG] {
+func MMD[Rc RC /* ERROR got 1 arguments */ [RG], RG any, G any]() M /* ERROR got 2 arguments */ [Rc, RG] {
 
-	var nFn NFn /* ERROR got 2 arguments */ /* ERROR Rc does not match */ [Rc, RG]
+	var nFn NFn /* ERROR got 2 arguments */ [Rc, RG]
 
 	var empty Rc
 	switch any(empty).(type) {

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51229.go2

@@ -0,0 +1,164 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+// Constraint type inference should be independent of the
+// ordering of the type parameter declarations. Try all
+// permutations in the test case below.
+// Permutations produced by https://go.dev/play/p/PHcZNGJTEBZ.
+
+func f00[S1 ~[]E1, S2 ~[]E2, E1 ~byte, E2 ~byte](S1, S2) {}
+func f01[S2 ~[]E2, S1 ~[]E1, E1 ~byte, E2 ~byte](S1, S2) {}
+func f02[E1 ~byte, S1 ~[]E1, S2 ~[]E2, E2 ~byte](S1, S2) {}
+func f03[S1 ~[]E1, E1 ~byte, S2 ~[]E2, E2 ~byte](S1, S2) {}
+func f04[S2 ~[]E2, E1 ~byte, S1 ~[]E1, E2 ~byte](S1, S2) {}
+func f05[E1 ~byte, S2 ~[]E2, S1 ~[]E1, E2 ~byte](S1, S2) {}
+func f06[E2 ~byte, S2 ~[]E2, S1 ~[]E1, E1 ~byte](S1, S2) {}
+func f07[S2 ~[]E2, E2 ~byte, S1 ~[]E1, E1 ~byte](S1, S2) {}
+func f08[S1 ~[]E1, E2 ~byte, S2 ~[]E2, E1 ~byte](S1, S2) {}
+func f09[E2 ~byte, S1 ~[]E1, S2 ~[]E2, E1 ~byte](S1, S2) {}
+func f10[S2 ~[]E2, S1 ~[]E1, E2 ~byte, E1 ~byte](S1, S2) {}
+func f11[S1 ~[]E1, S2 ~[]E2, E2 ~byte, E1 ~byte](S1, S2) {}
+func f12[S1 ~[]E1, E1 ~byte, E2 ~byte, S2 ~[]E2](S1, S2) {}
+func f13[E1 ~byte, S1 ~[]E1, E2 ~byte, S2 ~[]E2](S1, S2) {}
+func f14[E2 ~byte, S1 ~[]E1, E1 ~byte, S2 ~[]E2](S1, S2) {}
+func f15[S1 ~[]E1, E2 ~byte, E1 ~byte, S2 ~[]E2](S1, S2) {}
+func f16[E1 ~byte, E2 ~byte, S1 ~[]E1, S2 ~[]E2](S1, S2) {}
+func f17[E2 ~byte, E1 ~byte, S1 ~[]E1, S2 ~[]E2](S1, S2) {}
+func f18[E2 ~byte, E1 ~byte, S2 ~[]E2, S1 ~[]E1](S1, S2) {}
+func f19[E1 ~byte, E2 ~byte, S2 ~[]E2, S1 ~[]E1](S1, S2) {}
+func f20[S2 ~[]E2, E2 ~byte, E1 ~byte, S1 ~[]E1](S1, S2) {}
+func f21[E2 ~byte, S2 ~[]E2, E1 ~byte, S1 ~[]E1](S1, S2) {}
+func f22[E1 ~byte, S2 ~[]E2, E2 ~byte, S1 ~[]E1](S1, S2) {}
+func f23[S2 ~[]E2, E1 ~byte, E2 ~byte, S1 ~[]E1](S1, S2) {}
+
+type myByte byte
+
+func _(a []byte, b []myByte) {
+	f00(a, b)
+	f01(a, b)
+	f02(a, b)
+	f03(a, b)
+	f04(a, b)
+	f05(a, b)
+	f06(a, b)
+	f07(a, b)
+	f08(a, b)
+	f09(a, b)
+	f10(a, b)
+	f11(a, b)
+	f12(a, b)
+	f13(a, b)
+	f14(a, b)
+	f15(a, b)
+	f16(a, b)
+	f17(a, b)
+	f18(a, b)
+	f19(a, b)
+	f20(a, b)
+	f21(a, b)
+	f22(a, b)
+	f23(a, b)
+}
+
+// Constraint type inference may have to iterate.
+// Again, the order of the type parameters shouldn't matter.
+
+func g0[S ~[]E, M ~map[string]S, E any](m M) {}
+func g1[M ~map[string]S, S ~[]E, E any](m M) {}
+func g2[E any, S ~[]E, M ~map[string]S](m M) {}
+func g3[S ~[]E, E any, M ~map[string]S](m M) {}
+func g4[M ~map[string]S, E any, S ~[]E](m M) {}
+func g5[E any, M ~map[string]S, S ~[]E](m M) {}
+
+func _(m map[string][]byte) {
+	g0(m)
+	g1(m)
+	g2(m)
+	g3(m)
+	g4(m)
+	g5(m)
+}
+
+// Worst-case scenario.
+// There are 10 unknown type parameters. In each iteration of
+// constraint type inference we infer one more, from right to left.
+// Each iteration looks repeatedly at all 11 type parameters,
+// requiring a total of 10*11 = 110 iterations with the current
+// implementation. Pathological case.
+
+func h[K any, J ~*K, I ~*J, H ~*I, G ~*H, F ~*G, E ~*F, D ~*E, C ~*D, B ~*C, A ~*B](x A) {}
+
+func _(x **********int) {
+	h(x)
+}
+
+// Examples with channel constraints and tilde.
+
+func ch1[P chan<- int]() (_ P)           { return } // core(P) == chan<- int   (single type, no tilde)
+func ch2[P ~chan int]()                  { return } // core(P) == ~chan<- int  (tilde)
+func ch3[P chan E, E any](E)             { return } // core(P) == chan<- E     (single type, no tilde)
+func ch4[P chan E | ~chan<- E, E any](E) { return } // core(P) == ~chan<- E    (tilde)
+func ch5[P chan int | chan<- int]()      { return } // core(P) == chan<- int   (not a single type)
+
+func _() {
+	// P can be inferred as there's a single specific type and no tilde.
+	var _ chan int = ch1 /* ERROR cannot use ch1.*value of type chan<- int */ ()
+	var _ chan<- int = ch1()
+
+	// P cannot be inferred as there's a tilde.
+	ch2( /* ERROR cannot infer P */ )
+	type myChan chan int
+	ch2[myChan]()
+
+	// P can be inferred as there's a single specific type and no tilde.
+	var e int
+	ch3(e)
+
+	// P cannot be inferred as there's more than one specific type and a tilde.
+	ch4( /* ERROR cannot infer P */ e)
+	_ = ch4[chan int]
+
+	// P cannot be inferred as there's more than one specific type.
+	ch5( /* ERROR cannot infer P */ )
+	ch5[chan<- int]()
+}
+
+// test case from issue
+
+func equal[M1 ~map[K1]V1, M2 ~map[K2]V2, K1, K2 ~uint32, V1, V2 ~string](m1 M1, m2 M2) bool {
+	if len(m1) != len(m2) {
+		return false
+	}
+	for k, v1 := range m1 {
+		if v2, ok := m2[K2(k)]; !ok || V2(v1) != v2 {
+			return false
+		}
+	}
+	return true
+}
+
+func equalFixed[K1, K2 ~uint32, V1, V2 ~string](m1 map[K1]V1, m2 map[K2]V2) bool {
+	if len(m1) != len(m2) {
+		return false
+	}
+	for k, v1 := range m1 {
+		if v2, ok := m2[K2(k)]; !ok || v1 != V1(v2) {
+			return false
+		}
+	}
+	return true
+}
+
+type (
+	someNumericID uint32
+	someStringID  string
+)
+
+func _() {
+	foo := map[uint32]string{10: "bar"}
+	bar := map[someNumericID]someStringID{10: "bar"}
+	equal(foo, bar)
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51232.go2

@@ -11,19 +11,20 @@ type RC[RG any] interface {
 type Fn[RCT RC[RG], RG any] func(RCT)
 
 type F[RCT RC[RG], RG any] interface {
-	Fn() Fn[RCT]
+	Fn() Fn /* ERROR got 1 arguments */ [RCT]
 }
 
 type concreteF[RCT RC[RG], RG any] struct {
-	makeFn func() Fn[RCT]
+	makeFn func() Fn /* ERROR got 1 arguments */ [RCT]
 }
 
-func (c *concreteF[RCT, RG]) Fn() Fn[RCT] {
+func (c *concreteF[RCT, RG]) Fn() Fn /* ERROR got 1 arguments */ [RCT] {
 	return c.makeFn()
 }
 
-func NewConcrete[RCT RC[RG], RG any](Rc RCT) F[RCT] {
-	return &concreteF[RCT]{
+func NewConcrete[RCT RC[RG], RG any](Rc RCT) F /* ERROR got 1 arguments */ [RCT] {
+	// TODO(rfindley): eliminate the duplicate error below.
+	return & /* ERROR cannot use .* as F\[RCT\] */ concreteF /* ERROR got 1 arguments */ [RCT]{
 		makeFn: nil,
 	}
 }

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51233.go2

@@ -4,22 +4,24 @@
 
 package p
 
+// As of issue #51527, type-type inference has been disabled.
+
 type RC[RG any] interface {
 	~[]RG
 }
 
 type Fn[RCT RC[RG], RG any] func(RCT)
 
-type FFn[RCT RC[RG], RG any] func() Fn[RCT]
+type FFn[RCT RC[RG], RG any] func() Fn /* ERROR got 1 arguments */ [RCT]
 
 type F[RCT RC[RG], RG any] interface {
-	Fn() Fn[RCT]
+	Fn() Fn /* ERROR got 1 arguments */ [RCT]
 }
 
 type concreteF[RCT RC[RG], RG any] struct {
-	makeFn FFn[RCT]
+	makeFn FFn /* ERROR got 1 arguments */ [RCT]
 }
 
-func (c *concreteF[RCT, RG]) Fn() Fn[RCT] {
+func (c *concreteF[RCT, RG]) Fn() Fn /* ERROR got 1 arguments */ [RCT] {
 	return c.makeFn()
 }

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51339.go2

@@ -10,7 +10,9 @@ package p
 type T[P any, B *P] struct{}
 
 func (T /* ERROR cannot use generic type */ ) m0() {}
-func (T /* ERROR got 1 type parameter, but receiver base type declares 2 */ [_]) m1() {}
+
+// TODO(rfindley): eliminate the duplicate errors here.
+func (T /* ERROR got 1 type parameter, but receiver base type declares 2 */ /* ERROR got 1 arguments but 2 type parameters */ [_]) m1() {}
 func (T[_, _]) m2() {}
 // TODO(gri) this error is unfortunate (issue #51343)
 func (T /* ERROR got 3 arguments but 2 type parameters */ [_, _, _]) m3() {}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51376.go2

@@ -0,0 +1,24 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type Map map[string]int
+
+func f[M ~map[K]V, K comparable, V any](M) {}
+func g[M map[K]V, K comparable, V any](M) {}
+
+func _[M1 ~map[K]V, M2 map[K]V, K comparable, V any]() {
+        var m1 M1
+        f(m1)
+        g( /* ERROR M1 does not implement map\[K\]V */ m1) // M1 has tilde
+
+        var m2 M2
+        f(m2)
+        g(m2) // M1 does not have tilde
+
+        var m3 Map
+        f(m3)
+        g( /* ERROR Map does not implement map\[string\]int */ m3) // M in g does not have tilde
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51437.go

@@ -0,0 +1,17 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type T struct{}
+
+func (T) m() []int { return nil }
+
+func f(x T) {
+	for _, x := range func() []int {
+		return x.m() // x declared in parameter list of f
+	}() {
+		_ = x // x declared by range clause
+	}
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51472.go2

@@ -0,0 +1,54 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func _[T comparable](x T) {
+        _ = x == x
+}
+
+func _[T interface{interface{comparable}}](x T) {
+        _ = x == x
+}
+
+func _[T interface{comparable; interface{comparable}}](x T) {
+        _ = x == x
+}
+
+func _[T interface{comparable; ~int}](x T) {
+        _ = x == x
+}
+
+func _[T interface{comparable; ~[]byte}](x T) {
+        _ = x /* ERROR cannot compare */ == x
+}
+
+// TODO(gri) The error message here should be better. See issue #51525.
+func _[T interface{comparable; ~int; ~string}](x T) {
+        _ = x /* ERROR cannot compare */ == x
+}
+
+// TODO(gri) The error message here should be better. See issue #51525.
+func _[T interface{~int; ~string}](x T) {
+        _ = x /* ERROR cannot compare */ == x
+}
+
+func _[T interface{comparable; interface{~int}; interface{int|float64}}](x T) {
+        _ = x == x
+}
+
+func _[T interface{interface{comparable; ~int}; interface{~float64; comparable; m()}}](x T) {
+        _ = x /* ERROR cannot compare */ == x
+}
+
+// test case from issue
+
+func f[T interface{comparable; []byte|string}](x T) {
+        _ = x == x
+}
+
+func _(s []byte) {
+	f( /* ERROR \[\]byte does not implement interface{comparable; \[\]byte\|string} */ s)
+        _ = f[[ /* ERROR does not implement */ ]byte]
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51509.go

@@ -0,0 +1,7 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type T /* ERROR illegal cycle */ T.x

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51578.go2

@@ -0,0 +1,17 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+var _ = (*interface /* ERROR interface contains type constraints */ {int})(nil)
+
+// abbreviated test case from issue
+
+type TypeSet interface{ int | string }
+
+func _() {
+	f((*TypeSet /* ERROR interface contains type constraints */)(nil))
+}
+
+func f(any) {}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51593.go2

@@ -0,0 +1,13 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func f[P interface{ m(R) }, R any]() {}
+
+type T = interface { m(int) }
+
+func _() {
+	_ = f[ /* ERROR cannot infer R */ T] // don't crash in type inference
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51607.go2

@@ -0,0 +1,65 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+// Interface types must be ignored during overlap test.
+
+type (
+	T1 interface{int}
+	T2 interface{~int}
+	T3 interface{T1 | bool | string}
+	T4 interface{T2 | ~bool | ~string}
+)
+
+type (
+	// overlap errors for non-interface terms
+	// (like the interface terms, but explicitly inlined)
+	_ interface{int | int /* ERROR overlapping terms int and int */ }
+	_ interface{int | ~ /* ERROR overlapping terms ~int and int */ int}
+	_ interface{~int | int /* ERROR overlapping terms int and ~int */ }
+	_ interface{~int | ~ /* ERROR overlapping terms ~int and ~int */ int}
+
+	_ interface{T1 | bool | string | T1 | bool /* ERROR overlapping terms bool and bool */ | string /* ERROR overlapping terms string and string */ }
+	_ interface{T1 | bool | string | T2 | ~ /* ERROR overlapping terms ~bool and bool */ bool | ~ /* ERROR overlapping terms ~string and string */ string}
+
+	// no errors for interface terms
+	_ interface{T1 | T1}
+	_ interface{T1 | T2}
+	_ interface{T2 | T1}
+	_ interface{T2 | T2}
+
+	_ interface{T3 | T3 | int}
+	_ interface{T3 | T4 | bool }
+	_ interface{T4 | T3 | string }
+	_ interface{T4 | T4 | float64 }
+)
+
+func _[_ T1 | bool | string | T1 | bool /* ERROR overlapping terms */ ]() {}
+func _[_ T1 | bool | string | T2 | ~ /* ERROR overlapping terms */ bool ]() {}
+func _[_ T2 | ~bool | ~string | T1 | bool /* ERROR overlapping terms */ ]() {}
+func _[_ T2 | ~bool | ~string | T2 | ~ /* ERROR overlapping terms */ bool ]() {}
+
+func _[_ T3 | T3 | int]() {}
+func _[_ T3 | T4 | bool]() {}
+func _[_ T4 | T3 | string]() {}
+func _[_ T4 | T4 | float64]() {}
+
+// test cases from issue
+
+type _ interface {
+	interface {bool | int} | interface {bool | string}
+}
+
+type _ interface {
+	interface {bool | int} ; interface {bool | string}
+}
+
+type _ interface {
+	interface {bool; int} ; interface {bool; string}
+}
+
+type _ interface {
+	interface {bool; int} | interface {bool; string}
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51658.go2

@@ -0,0 +1,39 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type F { // ERROR syntax error
+	float64
+} // ERROR syntax error
+
+func _[T F | int](x T) {
+	_ = x == 0 // don't crash when recording type of 0
+}
+
+// test case from issue
+
+type FloatType { // ERROR syntax error
+	float32 | float64
+} // ERROR syntax error
+
+type IntegerType interface {
+	int8 | int16 | int32 | int64 | int |
+		uint8 | uint16 | uint32 | uint64 | uint
+}
+
+type ComplexType interface {
+	complex64 | complex128
+}
+
+type Number interface {
+	FloatType | IntegerType | ComplexType
+}
+
+func GetDefaultNumber[T Number](value, defaultValue T) T {
+	if value == 0 {
+		return defaultValue
+	}
+	return value
+}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue52529.go2

@@ -0,0 +1,15 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type Foo[P any] struct {
+	_ *Bar[P]
+}
+
+type Bar[Q any] Foo[Q]
+
+func (v *Bar[R]) M() {
+	_ = (*Foo[R])(v)
+}

src/cmd/compile/internal/types2/typeparam.go

@@ -31,7 +31,8 @@ func (t *TypeParam) Obj() *TypeName { return t.obj }
 // or Signature type by calling SetTypeParams. Setting a type parameter on more
 // than one type will result in a panic.
 //
-// The constraint argument can be nil, and set later via SetConstraint.
+// The constraint argument can be nil, and set later via SetConstraint. If the
+// constraint is non-nil, it must be fully defined.
 func NewTypeParam(obj *TypeName, constraint Type) *TypeParam {
 	return (*Checker)(nil).newTypeParam(obj, constraint)
 }
@@ -71,8 +72,10 @@ func (t *TypeParam) Constraint() Type {
 
 // SetConstraint sets the type constraint for t.
 //
-// SetConstraint should not be called concurrently, but once SetConstraint
-// returns the receiver t is safe for concurrent use.
+// It must be called by users of NewTypeParam after the bound's underlying is
+// fully defined, and before using the type parameter in any way other than to
+// form other types. Once SetConstraint returns the receiver, t is safe for
+// concurrent use.
 func (t *TypeParam) SetConstraint(bound Type) {
 	if bound == nil {
 		panic("nil constraint")

src/cmd/compile/internal/types2/typeset.go

@@ -15,20 +15,25 @@ import (
 // API
 
 // A _TypeSet represents the type set of an interface.
+// Because of existing language restrictions, methods can be "factored out"
+// from the terms. The actual type set is the intersection of the type set
+// implied by the methods and the type set described by the terms and the
+// comparable bit. To test whether a type is included in a type set
+// ("implements" relation), the type must implement all methods _and_ be
+// an element of the type set described by the terms and the comparable bit.
+// If the term list describes the set of all types and comparable is true,
+// only comparable types are meant; in all other cases comparable is false.
 type _TypeSet struct {
-	comparable bool // if set, the interface is or embeds comparable
-	// TODO(gri) consider using a set for the methods for faster lookup
-	methods []*Func  // all methods of the interface; sorted by unique ID
-	terms   termlist // type terms of the type set
+	methods    []*Func  // all methods of the interface; sorted by unique ID
+	terms      termlist // type terms of the type set
+	comparable bool     // invariant: !comparable || terms.isAll()
 }
 
 // IsEmpty reports whether type set s is the empty set.
 func (s *_TypeSet) IsEmpty() bool { return s.terms.isEmpty() }
 
 // IsAll reports whether type set s is the set of all types (corresponding to the empty interface).
-func (s *_TypeSet) IsAll() bool {
-	return !s.comparable && len(s.methods) == 0 && s.terms.isAll()
-}
+func (s *_TypeSet) IsAll() bool { return s.IsMethodSet() && len(s.methods) == 0 }
 
 // IsMethodSet reports whether the interface t is fully described by its method set.
 func (s *_TypeSet) IsMethodSet() bool { return !s.comparable && s.terms.isAll() }
@@ -43,13 +48,6 @@ func (s *_TypeSet) IsComparable(seen map[Type]bool) bool {
 	})
 }
 
-// TODO(gri) IsTypeSet is not a great name for this predicate. Find a better one.
-
-// IsTypeSet reports whether the type set s is represented by a finite set of underlying types.
-func (s *_TypeSet) IsTypeSet() bool {
-	return !s.comparable && len(s.methods) == 0
-}
-
 // NumMethods returns the number of methods available.
 func (s *_TypeSet) NumMethods() int { return len(s.methods) }
 
@@ -215,12 +213,12 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 
 	var todo []*Func
 	var seen objset
-	var methods []*Func
+	var allMethods []*Func
 	mpos := make(map[*Func]syntax.Pos) // method specification or method embedding position, for good error messages
 	addMethod := func(pos syntax.Pos, m *Func, explicit bool) {
 		switch other := seen.insert(m); {
 		case other == nil:
-			methods = append(methods, m)
+			allMethods = append(allMethods, m)
 			mpos[m] = pos
 		case explicit:
 			if check == nil {
@@ -259,7 +257,8 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 	}
 
 	// collect embedded elements
-	var allTerms = allTermlist
+	allTerms := allTermlist
+	allComparable := false
 	for i, typ := range ityp.embeddeds {
 		// The embedding position is nil for imported interfaces
 		// and also for interface copies after substitution (but
@@ -268,6 +267,7 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 		if ityp.embedPos != nil {
 			pos = (*ityp.embedPos)[i]
 		}
+		var comparable bool
 		var terms termlist
 		switch u := under(typ).(type) {
 		case *Interface:
@@ -279,9 +279,7 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 				check.versionErrorf(pos, "go1.18", "embedding constraint interface %s", typ)
 				continue
 			}
-			if tset.comparable {
-				ityp.tset.comparable = true
-			}
+			comparable = tset.comparable
 			for _, m := range tset.methods {
 				addMethod(pos, m, false) // use embedding position pos rather than m.pos
 			}
@@ -295,6 +293,8 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 			if tset == &invalidTypeSet {
 				continue // ignore invalid unions
 			}
+			assert(!tset.comparable)
+			assert(len(tset.methods) == 0)
 			terms = tset.terms
 		default:
 			if u == Typ[Invalid] {
@@ -306,11 +306,11 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 			}
 			terms = termlist{{false, typ}}
 		}
-		// The type set of an interface is the intersection
-		// of the type sets of all its elements.
-		// Intersection cannot produce longer termlists and
-		// thus cannot overflow.
-		allTerms = allTerms.intersect(terms)
+
+		// The type set of an interface is the intersection of the type sets of all its elements.
+		// Due to language restrictions, only embedded interfaces can add methods, they are handled
+		// separately. Here we only need to intersect the term lists and comparable bits.
+		allTerms, allComparable = intersectTermLists(allTerms, allComparable, terms, comparable)
 	}
 	ityp.embedPos = nil // not needed anymore (errors have been reported)
 
@@ -323,15 +323,46 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 		}
 	}
 
-	if methods != nil {
-		sortMethods(methods)
-		ityp.tset.methods = methods
+	ityp.tset.comparable = allComparable
+	if len(allMethods) != 0 {
+		sortMethods(allMethods)
+		ityp.tset.methods = allMethods
 	}
 	ityp.tset.terms = allTerms
 
 	return ityp.tset
 }
 
+// TODO(gri) The intersectTermLists function belongs to the termlist implementation.
+//           The comparable type set may also be best represented as a term (using
+//           a special type).
+
+// intersectTermLists computes the intersection of two term lists and respective comparable bits.
+// xcomp, ycomp are valid only if xterms.isAll() and yterms.isAll() respectively.
+func intersectTermLists(xterms termlist, xcomp bool, yterms termlist, ycomp bool) (termlist, bool) {
+	terms := xterms.intersect(yterms)
+	// If one of xterms or yterms is marked as comparable,
+	// the result must only include comparable types.
+	comp := xcomp || ycomp
+	if comp && !terms.isAll() {
+		// only keep comparable terms
+		i := 0
+		for _, t := range terms {
+			assert(t.typ != nil)
+			if Comparable(t.typ) {
+				terms[i] = t
+				i++
+			}
+		}
+		terms = terms[:i]
+		if !terms.isAll() {
+			comp = false
+		}
+	}
+	assert(!comp || terms.isAll()) // comparable invariant
+	return terms, comp
+}
+
 func sortMethods(list []*Func) {
 	sort.Sort(byUniqueMethodName(list))
 }
@@ -375,7 +406,7 @@ func computeUnionTypeSet(check *Checker, unionSets map[*Union]*_TypeSet, pos syn
 			// For now we don't permit type parameters as constraints.
 			assert(!isTypeParam(t.typ))
 			terms = computeInterfaceTypeSet(check, pos, ui).terms
-		} else if t.typ == Typ[Invalid] {
+		} else if u == Typ[Invalid] {
 			continue
 		} else {
 			if t.tilde && !Identical(t.typ, u) {

src/cmd/compile/internal/types2/typeset_test.go

@@ -25,9 +25,9 @@ func TestTypeSetString(t *testing.T) {
 		"{int; string}": "∅",
 
 		"{comparable}":              "{comparable}",
-		"{comparable; int}":         "{comparable; int}",
-		"{~int; comparable}":        "{comparable; ~int}",
-		"{int|string; comparable}":  "{comparable; int ∪ string}",
+		"{comparable; int}":         "{int}",
+		"{~int; comparable}":        "{~int}",
+		"{int|string; comparable}":  "{int ∪ string}",
 		"{comparable; int; string}": "∅",
 
 		"{m()}":                         "{func (p.T).m()}",
@@ -37,8 +37,8 @@ func TestTypeSetString(t *testing.T) {
 		"{m1(); comparable; m2() int }": "{comparable; func (p.T).m1(); func (p.T).m2() int}",
 		"{comparable; error}":           "{comparable; func (error).Error() string}",
 
-		"{m(); comparable; int|float32|string}": "{comparable; func (p.T).m(); int ∪ float32 ∪ string}",
-		"{m1(); int; m2(); comparable }":        "{comparable; func (p.T).m1(); func (p.T).m2(); int}",
+		"{m(); comparable; int|float32|string}": "{func (p.T).m(); int ∪ float32 ∪ string}",
+		"{m1(); int; m2(); comparable }":        "{func (p.T).m1(); func (p.T).m2(); int}",
 
 		"{E}; type E interface{}":           "𝓤",
 		"{E}; type E interface{int;string}": "∅",

src/cmd/compile/internal/types2/typexpr.go

@@ -147,10 +147,16 @@ func (check *Checker) typ(e syntax.Expr) Type {
 // constraint interface.
 func (check *Checker) varType(e syntax.Expr) Type {
 	typ := check.definedType(e, nil)
+	check.validVarType(e, typ)
+	return typ
+}
 
+// validVarType reports an error if typ is a constraint interface.
+// The expression e is used for error reporting, if any.
+func (check *Checker) validVarType(e syntax.Expr, typ Type) {
 	// If we have a type parameter there's nothing to do.
 	if isTypeParam(typ) {
-		return typ
+		return
 	}
 
 	// We don't want to call under() or complete interfaces while we are in
@@ -169,8 +175,6 @@ func (check *Checker) varType(e syntax.Expr) Type {
 			}
 		}
 	})
-
-	return typ
 }
 
 // definedType is like typ but also accepts a type name def.
@@ -256,7 +260,7 @@ func (check *Checker) typInternal(e0 syntax.Expr, def *Named) (T Type) {
 
 	case *syntax.SelectorExpr:
 		var x operand
-		check.selector(&x, e)
+		check.selector(&x, e, def)
 
 		switch x.mode {
 		case typexpr:
@@ -430,10 +434,14 @@ func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *
 	// evaluate arguments
 	targs := check.typeList(xlist)
 	if targs == nil {
-		def.setUnderlying(Typ[Invalid]) // avoid later errors due to lazy instantiation
+		def.setUnderlying(Typ[Invalid]) // avoid errors later due to lazy instantiation
 		return Typ[Invalid]
 	}
 
+	// enableTypeTypeInference controls whether to infer missing type arguments
+	// using constraint type inference. See issue #51527.
+	const enableTypeTypeInference = false
+
 	// create the instance
 	ctxt := check.bestContext(nil)
 	h := ctxt.instanceHash(orig, targs)
@@ -453,19 +461,18 @@ func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *
 	def.setUnderlying(inst)
 
 	inst.resolver = func(ctxt *Context, n *Named) (*TypeParamList, Type, *methodList) {
-		tparams := orig.TypeParams().list()
+		tparams := n.orig.TypeParams().list()
 
-		inferred := targs
-		if len(targs) < len(tparams) {
+		targs := n.targs.list()
+		if enableTypeTypeInference && len(targs) < len(tparams) {
 			// If inference fails, len(inferred) will be 0, and inst.underlying will
 			// be set to Typ[Invalid] in expandNamed.
-			inferred = check.infer(x.Pos(), tparams, targs, nil, nil)
+			inferred := check.infer(x.Pos(), tparams, targs, nil, nil)
 			if len(inferred) > len(targs) {
-				inst.targs = newTypeList(inferred)
+				n.targs = newTypeList(inferred)
 			}
 		}
 
-		check.recordInstance(x, inferred, inst)
 		return expandNamed(ctxt, n, x.Pos())
 	}
 
@@ -478,6 +485,7 @@ func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *
 		// Since check is non-nil, we can still mutate inst. Unpinning the resolver
 		// frees some memory.
 		inst.resolver = nil
+		check.recordInstance(x, inst.TypeArgs().list(), inst)
 
 		if check.validateTArgLen(x.Pos(), inst.tparams.Len(), inst.targs.Len()) {
 			if i, err := check.verify(x.Pos(), inst.tparams.list(), inst.targs.list()); err != nil {

src/cmd/compile/internal/types2/unify.go

@@ -247,6 +247,17 @@ func (d *tparamsList) set(i int, typ Type) {
 	}
 }
 
+// unknowns returns the number of type parameters for which no type has been set yet.
+func (d *tparamsList) unknowns() int {
+	n := 0
+	for _, ti := range d.indices {
+		if ti <= 0 {
+			n++
+		}
+	}
+	return n
+}
+
 // types returns the list of inferred types (via unification) for the type parameters
 // described by d, and an index. If all types were inferred, the returned index is < 0.
 // Otherwise, it is the index of the first type parameter which couldn't be inferred;
@@ -349,12 +360,16 @@ func (u *unifier) nify(x, y Type, p *ifacePair) (result bool) {
 	if enableCoreTypeUnification && !u.exact {
 		if isTypeParam(x) && !hasName(y) {
 			// When considering the type parameter for unification
-			// we look at the adjusted core type (adjCoreType).
+			// we look at the adjusted core term (adjusted core type
+			// with tilde information).
 			// If the adjusted core type is a named type N; the
 			// corresponding core type is under(N). Since !u.exact
 			// and y doesn't have a name, unification will end up
 			// comparing under(N) to y, so we can just use the core
-			// type instead. Optimization.
+			// type instead. And we can ignore the tilde because we
+			// already look at the underlying types on both sides
+			// and we have known types on both sides.
+			// Optimization.
 			if cx := coreType(x); cx != nil {
 				if traceInference {
 					u.tracef("core %s ≡ %s", x, y)

src/cmd/compile/internal/types2/union.go

@@ -100,25 +100,25 @@ func parseUnion(check *Checker, uexpr syntax.Expr) Type {
 
 				if !Identical(u, t.typ) {
 					check.errorf(tlist[i], "invalid use of ~ (underlying type of %s is %s)", t.typ, u)
-					continue // don't report another error for t
+					continue
 				}
 			}
 
 			// Stand-alone embedded interfaces are ok and are handled by the single-type case
 			// in the beginning. Embedded interfaces with tilde are excluded above. If we reach
-			// here, we must have at least two terms in the union.
-			if f != nil && !f.typeSet().IsTypeSet() {
+			// here, we must have at least two terms in the syntactic term list (but not necessarily
+			// in the term list of the union's type set).
+			if f != nil {
+				tset := f.typeSet()
 				switch {
-				case f.typeSet().NumMethods() != 0:
+				case tset.NumMethods() != 0:
 					check.errorf(tlist[i], "cannot use %s in union (%s contains methods)", t, t)
 				case t.typ == universeComparable.Type():
 					check.error(tlist[i], "cannot use comparable in union")
-				case f.typeSet().comparable:
+				case tset.comparable:
 					check.errorf(tlist[i], "cannot use %s in union (%s embeds comparable)", t, t)
-				default:
-					panic("not a type set but no methods and not comparable")
 				}
-				continue // don't report another error for t
+				continue // terms with interface types are not subject to the no-overlap rule
 			}
 
 			// Report overlapping (non-disjoint) terms such as
@@ -158,10 +158,16 @@ func parseTilde(check *Checker, tx syntax.Expr) *Term {
 
 // overlappingTerm reports the index of the term x in terms which is
 // overlapping (not disjoint) from y. The result is < 0 if there is no
-// such term.
+// such term. The type of term y must not be an interface, and terms
+// with an interface type are ignored in the terms list.
 func overlappingTerm(terms []*Term, y *Term) int {
+	assert(!IsInterface(y.typ))
 	for i, x := range terms {
-		// disjoint requires non-nil, non-top arguments
+		if IsInterface(x.typ) {
+			continue
+		}
+		// disjoint requires non-nil, non-top arguments,
+		// and non-interface types as term types.
 		if debug {
 			if x == nil || x.typ == nil || y == nil || y.typ == nil {
 				panic("empty or top union term")

src/cmd/compile/internal/types2/universe.go

@@ -111,7 +111,7 @@ func defPredeclaredTypes() {
 		typ := NewNamed(obj, nil, nil)
 
 		// interface{} // marked as comparable
-		ityp := &Interface{obj: obj, complete: true, tset: &_TypeSet{true, nil, allTermlist}}
+		ityp := &Interface{obj: obj, complete: true, tset: &_TypeSet{nil, allTermlist, true}}
 
 		typ.SetUnderlying(ityp)
 		def(obj)

src/cmd/compile/internal/walk/closure.go

@@ -235,15 +235,7 @@ func methodValueWrapper(dot *ir.SelectorExpr) *ir.Name {
 	saveLineNo := base.Pos
 	ir.CurFunc = nil
 
-	// Set line number equal to the line number where the method is declared.
-	if pos := dot.Selection.Pos; pos.IsKnown() {
-		base.Pos = pos
-	}
-	// Note: !dot.Selection.Pos.IsKnown() happens for method expressions where
-	// the method is implicitly declared. The Error method of the
-	// built-in error type is one such method.  We leave the line
-	// number at the use of the method expression in this
-	// case. See issue 29389.
+	base.Pos = base.AutogeneratedPos
 
 	tfn := ir.NewFuncType(base.Pos, nil,
 		typecheck.NewFuncParams(t0.Params(), true),

src/cmd/compile/internal/walk/complit.go

@@ -621,6 +621,12 @@ func oaslit(n *ir.AssignStmt, init *ir.Nodes) bool {
 		// not a special composite literal assignment
 		return false
 	}
+	if x.Addrtaken() {
+		// If x is address-taken, the RHS may (implicitly) uses LHS.
+		// Not safe to do a special composite literal assignment
+		// (which may expand to multiple assignments).
+		return false
+	}
 
 	switch n.Y.Op() {
 	default:
@@ -629,7 +635,7 @@ func oaslit(n *ir.AssignStmt, init *ir.Nodes) bool {
 
 	case ir.OSTRUCTLIT, ir.OARRAYLIT, ir.OSLICELIT, ir.OMAPLIT:
 		if ir.Any(n.Y, func(y ir.Node) bool { return ir.Uses(y, x) }) {
-			// not a special composite literal assignment
+			// not safe to do a special composite literal assignment if RHS uses LHS.
 			return false
 		}
 		anylit(n.Y, n.X, init)

src/cmd/go.mod

@@ -8,7 +8,7 @@ require (
 	golang.org/x/mod v0.6.0-dev.0.20211102181907-3a5865c02020
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
 	golang.org/x/term v0.0.0-20210927222741-03fcf44c2211
-	golang.org/x/tools v0.1.9-0.20220124164225-97de9ec46646
+	golang.org/x/tools v0.1.9-0.20220329150752-294080fd2f5a
 )
 
 require (

src/cmd/go.sum

@@ -18,7 +18,7 @@ golang.org/x/sys v0.0.0-20211205182925-97ca703d548d h1:FjkYO/PPp4Wi0EAUOVLxePm7q
 golang.org/x/sys v0.0.0-20211205182925-97ca703d548d/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211 h1:JGgROgKl9N8DuW20oFS5gxc+lE67/N3FcwmBPMe7ArY=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
-golang.org/x/tools v0.1.9-0.20220124164225-97de9ec46646 h1:f8aekWvlQQ8ZhD8SL7lOu18dtWslZYl029PN2F0VnS4=
-golang.org/x/tools v0.1.9-0.20220124164225-97de9ec46646/go.mod h1:nABZi5QlRsZVlzPpHl034qft6wpY4eDcsTt5AaioBiU=
+golang.org/x/tools v0.1.9-0.20220329150752-294080fd2f5a h1:IlVBSvpiWIkpqADzaiismkf1xcqsZjBDIXzO+7kZEpY=
+golang.org/x/tools v0.1.9-0.20220329150752-294080fd2f5a/go.mod h1:nABZi5QlRsZVlzPpHl034qft6wpY4eDcsTt5AaioBiU=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

src/cmd/go/alldocs.go

@@ -138,11 +138,13 @@
 // 	-buildmode mode
 // 		build mode to use. See 'go help buildmode' for more.
 // 	-buildvcs
-// 		Whether to stamp binaries with version control information. By default,
-// 		version control information is stamped into a binary if the main package
-// 		and the main module containing it are in the repository containing the
-// 		current directory (if there is a repository). Use -buildvcs=false to
-// 		omit version control information.
+// 		Whether to stamp binaries with version control information
+// 		("true", "false", or "auto"). By default ("auto"), version control
+// 		information is stamped into a binary if the main package, the main module
+// 		containing it, and the current directory are all in the same repository.
+// 		Use -buildvcs=false to always omit version control information, or
+// 		-buildvcs=true to error out if version control information is available but
+// 		cannot be included due to a missing tool or ambiguous directory structure.
 // 	-compiler name
 // 		name of compiler to use, as in runtime.Compiler (gccgo or gc).
 // 	-gccgoflags '[pattern=]arg list'
@@ -1356,7 +1358,7 @@
 //
 // Workspace maintenance
 //
-// Go workspace provides access to operations on workspaces.
+// Work provides access to operations on workspaces.
 //
 // Note that support for workspaces is built into many other commands, not
 // just 'go work'.
@@ -1364,6 +1366,12 @@
 // See 'go help modules' for information about Go's module system of which
 // workspaces are a part.
 //
+// See https://go.dev/ref/mod#workspaces for an in-depth reference on
+// workspaces.
+//
+// See https://go.dev/doc/tutorial/workspaces for an introductory
+// tutorial on workspaces.
+//
 // A workspace is specified by a go.work file that specifies a set of
 // module directories with the "use" directive. These modules are used as
 // root modules by the go command for builds and related operations.  A
@@ -1485,9 +1493,8 @@
 // 		Version string
 // 	}
 //
-// See the workspaces design proposal at
-// https://go.googlesource.com/proposal/+/master/design/45713-workspace.md for
-// more information.
+// See the workspaces reference at https://go.dev/ref/mod#workspaces
+// for more information.
 //
 //
 // Initialize workspace file
@@ -1507,6 +1514,9 @@
 // Each argument path is added to a use directive in the go.work file. The
 // current go version will also be listed in the go.work file.
 //
+// See the workspaces reference at https://go.dev/ref/mod#workspaces
+// for more information.
+//
 //
 // Sync workspace build list to modules
 //
@@ -1530,12 +1540,15 @@
 // build list's version of each module is always the same or higher than
 // that in each workspace module.
 //
+// See the workspaces reference at https://go.dev/ref/mod#workspaces
+// for more information.
+//
 //
 // Add modules to workspace file
 //
 // Usage:
 //
-// 	go work use [-r] [moddirs]
+// 	go work use [-r] moddirs
 //
 // Use provides a command-line interface for adding
 // directories, optionally recursively, to a go.work file.
@@ -1549,6 +1562,9 @@
 // were specified as arguments: namely, use directives will be added for
 // directories that exist, and removed for directories that do not exist.
 //
+// See the workspaces reference at https://go.dev/ref/mod#workspaces
+// for more information.
+//
 //
 // Compile and run Go program
 //

src/cmd/go/internal/cfg/cfg.go

@@ -24,9 +24,9 @@ import (
 
 // These are general "build flags" used by build and other commands.
 var (
-	BuildA                 bool   // -a flag
-	BuildBuildmode         string // -buildmode flag
-	BuildBuildvcs          bool   // -buildvcs flag
+	BuildA                 bool     // -a flag
+	BuildBuildmode         string   // -buildmode flag
+	BuildBuildvcs          = "auto" // -buildvcs flag: "true", "false", or "auto"
 	BuildContext           = defaultContext()
 	BuildMod               string                  // -mod flag
 	BuildModExplicit       bool                    // whether -mod was set explicitly

src/cmd/go/internal/list/list.go

@@ -503,6 +503,7 @@ func runList(ctx context.Context, cmd *base.Command, args []string) {
 	pkgOpts := load.PackageOpts{
 		IgnoreImports:   *listFind,
 		ModResolveTests: *listTest,
+		LoadVCS:         true,
 	}
 	pkgs := load.PackagesAndErrors(ctx, pkgOpts, args)
 	if !*listE {

src/cmd/go/internal/load/pkg.go

@@ -17,6 +17,7 @@ import (
 	"internal/goroot"
 	"io/fs"
 	"os"
+	"os/exec"
 	"path"
 	pathpkg "path"
 	"path/filepath"
@@ -193,6 +194,18 @@ func (p *Package) Desc() string {
 	return p.ImportPath
 }
 
+// IsTestOnly reports whether p is a test-only package.
+//
+// A “test-only” package is one that:
+//   - is a test-only variant of an ordinary package, or
+//   - is a synthesized "main" package for a test binary, or
+//   - contains only _test.go files.
+func (p *Package) IsTestOnly() bool {
+	return p.ForTest != "" ||
+		p.Internal.TestmainGo != nil ||
+		len(p.TestGoFiles)+len(p.XTestGoFiles) > 0 && len(p.GoFiles)+len(p.CgoFiles) == 0
+}
+
 type PackageInternal struct {
 	// Unexported fields are not part of the public API.
 	Build             *build.Package
@@ -1926,8 +1939,12 @@ func (p *Package) load(ctx context.Context, opts PackageOpts, path string, stk *
 	}
 	p.Internal.Imports = imports
 	p.collectDeps()
-	if p.Error == nil && p.Name == "main" && len(p.DepsErrors) == 0 {
-		p.setBuildInfo()
+	if p.Error == nil && p.Name == "main" && !p.Internal.ForceLibrary && len(p.DepsErrors) == 0 {
+		// TODO(bcmills): loading VCS metadata can be fairly slow.
+		// Consider starting this as a background goroutine and retrieving the result
+		// asynchronously when we're actually ready to build the package, or when we
+		// actually need to evaluate whether the package's metadata is stale.
+		p.setBuildInfo(opts.LoadVCS)
 	}
 
 	// unsafe is a fake package.
@@ -2216,7 +2233,7 @@ var vcsStatusCache par.Cache
 //
 // Note that the GoVersion field is not set here to avoid encoding it twice.
 // It is stored separately in the binary, mostly for historical reasons.
-func (p *Package) setBuildInfo() {
+func (p *Package) setBuildInfo(includeVCS bool) {
 	// TODO: build and vcs information is not embedded for executables in GOROOT.
 	// cmd/dist uses -gcflags=all= -ldflags=all= by default, which means these
 	// executables always appear stale unless the user sets the same flags.
@@ -2312,7 +2329,17 @@ func (p *Package) setBuildInfo() {
 			appendSetting("-gcflags", BuildGcflags.String())
 		}
 		if BuildLdflags.present {
-			appendSetting("-ldflags", BuildLdflags.String())
+			// https://go.dev/issue/52372: only include ldflags if -trimpath is not set,
+			// since it can include system paths through various linker flags (notably
+			// -extar, -extld, and -extldflags).
+			//
+			// TODO: since we control cmd/link, in theory we can parse ldflags to
+			// determine whether they may refer to system paths. If we do that, we can
+			// redact only those paths from the recorded -ldflags setting and still
+			// record the system-independent parts of the flags.
+			if !cfg.BuildTrimpath {
+				appendSetting("-ldflags", BuildLdflags.String())
+			}
 		}
 		if cfg.BuildMSan {
 			appendSetting("-msan", "true")
@@ -2328,7 +2355,14 @@ func (p *Package) setBuildInfo() {
 			cgo = "1"
 		}
 		appendSetting("CGO_ENABLED", cgo)
-		if cfg.BuildContext.CgoEnabled {
+		// https://go.dev/issue/52372: only include CGO flags if -trimpath is not set.
+		// (If -trimpath is set, it is possible that these flags include system paths.)
+		// If cgo is involved, reproducibility is already pretty well ruined anyway,
+		// given that we aren't stamping header or library versions.
+		//
+		// TODO(bcmills): perhaps we could at least parse the flags and stamp the
+		// subset of flags that are known not to be paths?
+		if cfg.BuildContext.CgoEnabled && !cfg.BuildTrimpath {
 			for _, name := range []string{"CGO_CFLAGS", "CGO_CPPFLAGS", "CGO_CXXFLAGS", "CGO_LDFLAGS"} {
 				appendSetting(name, cfg.Getenv(name))
 			}
@@ -2346,8 +2380,8 @@ func (p *Package) setBuildInfo() {
 	// Add VCS status if all conditions are true:
 	//
 	// - -buildvcs is enabled.
-	// - p is contained within a main module (there may be multiple main modules
-	//   in a workspace, but local replacements don't count).
+	// - p is a non-test contained within a main module (there may be multiple
+	//   main modules in a workspace, but local replacements don't count).
 	// - Both the current directory and p's module's root directory are contained
 	//   in the same local repository.
 	// - We know the VCS commands needed to get the status.
@@ -2359,7 +2393,7 @@ func (p *Package) setBuildInfo() {
 	var vcsCmd *vcs.Cmd
 	var err error
 	const allowNesting = true
-	if cfg.BuildBuildvcs && p.Module != nil && p.Module.Version == "" && !p.Standard {
+	if includeVCS && cfg.BuildBuildvcs != "false" && p.Module != nil && p.Module.Version == "" && !p.Standard && !p.IsTestOnly() {
 		repoDir, vcsCmd, err = vcs.FromDir(base.Cwd(), "", allowNesting)
 		if err != nil && !errors.Is(err, os.ErrNotExist) {
 			setVCSError(err)
@@ -2371,7 +2405,14 @@ func (p *Package) setBuildInfo() {
 			// repository containing the working directory. Don't include VCS info.
 			// If the repo contains the module or vice versa, but they are not
 			// the same directory, it's likely an error (see below).
-			repoDir, vcsCmd = "", nil
+			goto omitVCS
+		}
+		if cfg.BuildBuildvcs == "auto" && vcsCmd != nil && vcsCmd.Cmd != "" {
+			if _, err := exec.LookPath(vcsCmd.Cmd); err != nil {
+				// We fould a repository, but the required VCS tool is not present.
+				// "-buildvcs=auto" means that we should silently drop the VCS metadata.
+				goto omitVCS
+			}
 		}
 	}
 	if repoDir != "" && vcsCmd.Status != nil {
@@ -2385,8 +2426,11 @@ func (p *Package) setBuildInfo() {
 			return
 		}
 		if pkgRepoDir != repoDir {
-			setVCSError(fmt.Errorf("main package is in repository %q but current directory is in repository %q", pkgRepoDir, repoDir))
-			return
+			if cfg.BuildBuildvcs != "auto" {
+				setVCSError(fmt.Errorf("main package is in repository %q but current directory is in repository %q", pkgRepoDir, repoDir))
+				return
+			}
+			goto omitVCS
 		}
 		modRepoDir, _, err := vcs.FromDir(p.Module.Dir, "", allowNesting)
 		if err != nil {
@@ -2394,8 +2438,11 @@ func (p *Package) setBuildInfo() {
 			return
 		}
 		if modRepoDir != repoDir {
-			setVCSError(fmt.Errorf("main module is in repository %q but current directory is in repository %q", modRepoDir, repoDir))
-			return
+			if cfg.BuildBuildvcs != "auto" {
+				setVCSError(fmt.Errorf("main module is in repository %q but current directory is in repository %q", modRepoDir, repoDir))
+				return
+			}
+			goto omitVCS
 		}
 
 		type vcsStatusError struct {
@@ -2422,6 +2469,7 @@ func (p *Package) setBuildInfo() {
 		}
 		appendSetting("vcs.modified", strconv.FormatBool(st.Uncommitted))
 	}
+omitVCS:
 
 	p.Internal.BuildInfo = info.String()
 }
@@ -2648,6 +2696,9 @@ type PackageOpts struct {
 	// are not be matched, and their dependencies may not be loaded. A warning
 	// may be printed for non-literal arguments that match no main packages.
 	MainOnly bool
+
+	// LoadVCS controls whether we also load version-control metadata for main packages.
+	LoadVCS bool
 }
 
 // PackagesAndErrors returns the packages named by the command line arguments

src/cmd/go/internal/load/test.go

@@ -368,9 +368,9 @@ func TestPackagesAndErrors(ctx context.Context, opts PackageOpts, p *Package, co
 	if err != nil && pmain.Error == nil {
 		pmain.Error = &PackageError{Err: err}
 	}
-	if data != nil {
-		pmain.Internal.TestmainGo = &data
-	}
+	// Set TestmainGo even if it is empty: the presence of a TestmainGo
+	// indicates that this package is, in fact, a test main.
+	pmain.Internal.TestmainGo = &data
 
 	return pmain, ptest, pxtest
 }

src/cmd/go/internal/modfetch/codehost/git.go

@@ -447,7 +447,7 @@ func (r *gitRepo) fetchRefsLocked() error {
 // statLocal returns a RevInfo describing rev in the local git repository.
 // It uses version as info.Version.
 func (r *gitRepo) statLocal(version, rev string) (*RevInfo, error) {
-	out, err := Run(r.dir, "git", "-c", "log.showsignature=false", "log", "-n1", "--format=format:%H %ct %D", rev, "--")
+	out, err := Run(r.dir, "git", "-c", "log.showsignature=false", "log", "--no-decorate", "-n1", "--format=format:%H %ct %D", rev, "--")
 	if err != nil {
 		return nil, &UnknownRevisionError{Rev: rev}
 	}

src/cmd/go/internal/modload/buildlist.go

@@ -397,7 +397,6 @@ func readModGraph(ctx context.Context, pruning modPruning, roots []module.Versio
 		seen := map[module.Version]bool{}
 		for _, m := range roots {
 			hasDepsInAll[m.Path] = true
-			seen[m] = true
 		}
 		// This loop will terminate because it will call enqueue on each version of
 		// each dependency of the modules in hasDepsInAll at most once (and only
@@ -406,11 +405,11 @@ func readModGraph(ctx context.Context, pruning modPruning, roots []module.Versio
 			needsEnqueueing := map[module.Version]bool{}
 			for p := range hasDepsInAll {
 				m := module.Version{Path: p, Version: mg.g.Selected(p)}
-				reqs, ok := mg.g.RequiredBy(m)
-				if !ok {
+				if !seen[m] {
 					needsEnqueueing[m] = true
 					continue
 				}
+				reqs, _ := mg.g.RequiredBy(m)
 				for _, r := range reqs {
 					s := module.Version{Path: r.Path, Version: mg.g.Selected(r.Path)}
 					if cmpVersion(s.Version, r.Version) > 0 && !seen[s] {

src/cmd/go/internal/modload/init.go

@@ -288,6 +288,11 @@ func BinDir() string {
 // operate in workspace mode. It should not be called by other commands,
 // for example 'go mod tidy', that don't operate in workspace mode.
 func InitWorkfile() {
+	if RootMode == NoRoot {
+		workFilePath = ""
+		return
+	}
+
 	switch gowork := cfg.Getenv("GOWORK"); gowork {
 	case "off":
 		workFilePath = ""

src/cmd/go/internal/modload/load.go

@@ -715,6 +715,12 @@ func ImportFromFiles(ctx context.Context, gofiles []string) {
 		},
 	})
 	requirements = loaded.requirements
+
+	if !ExplicitWriteGoMod {
+		if err := commitRequirements(ctx); err != nil {
+			base.Fatalf("go: %v", err)
+		}
+	}
 }
 
 // DirImportPath returns the effective import path for dir,

src/cmd/go/internal/modload/modfile.go

@@ -802,7 +802,7 @@ var latestVersionIgnoringRetractionsCache par.Cache // path → queryLatestVersi
 // an absolute path or a relative path starting with a '.' or '..'
 // path component.
 func ToDirectoryPath(path string) string {
-	if modfile.IsDirectoryPath(path) {
+	if path == "." || modfile.IsDirectoryPath(path) {
 		return path
 	}
 	// The path is not a relative path or an absolute path, so make it relative

src/cmd/go/internal/run/run.go

@@ -73,8 +73,6 @@ func printStderr(args ...any) (int, error) {
 }
 
 func runRun(ctx context.Context, cmd *base.Command, args []string) {
-	modload.InitWorkfile()
-
 	if shouldUseOutsideModuleMode(args) {
 		// Set global module flags for 'go run cmd@version'.
 		// This must be done before modload.Init, but we need to call work.BuildInit
@@ -84,7 +82,10 @@ func runRun(ctx context.Context, cmd *base.Command, args []string) {
 		modload.RootMode = modload.NoRoot
 		modload.AllowMissingModuleImports()
 		modload.Init()
+	} else {
+		modload.InitWorkfile()
 	}
+
 	work.BuildInit()
 	var b work.Builder
 	b.Init()

src/cmd/go/internal/vcs/vcs.go

@@ -312,7 +312,7 @@ func gitStatus(vcsGit *Cmd, rootDir string) (Status, error) {
 	// uncommitted files and skip tagging revision / committime.
 	var rev string
 	var commitTime time.Time
-	out, err = vcsGit.runOutputVerboseOnly(rootDir, "show -s --no-show-signature --format=%H:%ct")
+	out, err = vcsGit.runOutputVerboseOnly(rootDir, "-c log.showsignature=false show -s --format=%H:%ct")
 	if err != nil && !uncommitted {
 		return Status{}, err
 	} else if err == nil {

src/cmd/go/internal/work/build.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 
 	"cmd/go/internal/base"
@@ -91,11 +92,13 @@ and test commands:
 	-buildmode mode
 		build mode to use. See 'go help buildmode' for more.
 	-buildvcs
-		Whether to stamp binaries with version control information. By default,
-		version control information is stamped into a binary if the main package
-		and the main module containing it are in the repository containing the
-		current directory (if there is a repository). Use -buildvcs=false to
-		omit version control information.
+		Whether to stamp binaries with version control information
+		("true", "false", or "auto"). By default ("auto"), version control
+		information is stamped into a binary if the main package, the main module
+		containing it, and the current directory are all in the same repository.
+		Use -buildvcs=false to always omit version control information, or
+		-buildvcs=true to error out if version control information is available but
+		cannot be included due to a missing tool or ambiguous directory structure.
 	-compiler name
 		name of compiler to use, as in runtime.Compiler (gccgo or gc).
 	-gccgoflags '[pattern=]arg list'
@@ -302,7 +305,7 @@ func AddBuildFlags(cmd *base.Command, mask BuildFlagMask) {
 	cmd.Flag.Var((*base.StringsFlag)(&cfg.BuildToolexec), "toolexec", "")
 	cmd.Flag.BoolVar(&cfg.BuildTrimpath, "trimpath", false, "")
 	cmd.Flag.BoolVar(&cfg.BuildWork, "work", false, "")
-	cmd.Flag.BoolVar(&cfg.BuildBuildvcs, "buildvcs", true, "")
+	cmd.Flag.Var((*buildvcsFlag)(&cfg.BuildBuildvcs), "buildvcs", "")
 
 	// Undocumented, unstable debugging flags.
 	cmd.Flag.StringVar(&cfg.DebugActiongraph, "debug-actiongraph", "", "")
@@ -332,6 +335,29 @@ func (v *tagsFlag) String() string {
 	return "<TagsFlag>"
 }
 
+// buildvcsFlag is the implementation of the -buildvcs flag.
+type buildvcsFlag string
+
+func (f *buildvcsFlag) IsBoolFlag() bool { return true } // allow -buildvcs (without arguments)
+
+func (f *buildvcsFlag) Set(s string) error {
+	// https://go.dev/issue/51748: allow "-buildvcs=auto",
+	// in addition to the usual "true" and "false".
+	if s == "" || s == "auto" {
+		*f = "auto"
+		return nil
+	}
+
+	b, err := strconv.ParseBool(s)
+	if err != nil {
+		return errors.New("value is neither 'auto' nor a valid bool")
+	}
+	*f = (buildvcsFlag)(strconv.FormatBool(b)) // convert to canonical "true" or "false"
+	return nil
+}
+
+func (f *buildvcsFlag) String() string { return string(*f) }
+
 // fileExtSplit expects a filename and returns the name
 // and ext (without the dot). If the file has no
 // extension, ext will be empty.
@@ -379,7 +405,7 @@ func runBuild(ctx context.Context, cmd *base.Command, args []string) {
 	var b Builder
 	b.Init()
 
-	pkgs := load.PackagesAndErrors(ctx, load.PackageOpts{}, args)
+	pkgs := load.PackagesAndErrors(ctx, load.PackageOpts{LoadVCS: true}, args)
 	load.CheckPackageErrors(pkgs)
 
 	explicitO := len(cfg.BuildO) > 0
@@ -603,7 +629,7 @@ func runInstall(ctx context.Context, cmd *base.Command, args []string) {
 
 	modload.InitWorkfile()
 	BuildInit()
-	pkgs := load.PackagesAndErrors(ctx, load.PackageOpts{}, args)
+	pkgs := load.PackagesAndErrors(ctx, load.PackageOpts{LoadVCS: true}, args)
 	if cfg.ModulesEnabled && !modload.HasModRoot() {
 		haveErrors := false
 		allMissingErrors := true

src/cmd/go/internal/workcmd/edit.go

@@ -84,9 +84,8 @@ writing it back to go.mod. The JSON output corresponds to these Go types:
 		Version string
 	}
 
-See the workspaces design proposal at
-https://go.googlesource.com/proposal/+/master/design/45713-workspace.md for
-more information.
+See the workspaces reference at https://go.dev/ref/mod#workspaces
+for more information.
 `,
 }
 

src/cmd/go/internal/workcmd/init.go

@@ -27,6 +27,8 @@ modules will be created.
 Each argument path is added to a use directive in the go.work file. The
 current go version will also be listed in the go.work file.
 
+See the workspaces reference at https://go.dev/ref/mod#workspaces
+for more information.
 `,
 	Run: runInit,
 }

src/cmd/go/internal/workcmd/sync.go

@@ -33,6 +33,9 @@ if the dependency module's version is not already the same as the build
 list's version. Note that Minimal Version Selection guarantees that the
 build list's version of each module is always the same or higher than
 that in each workspace module.
+
+See the workspaces reference at https://go.dev/ref/mod#workspaces
+for more information.
 `,
 	Run: runSync,
 }

src/cmd/go/internal/workcmd/use.go

@@ -12,7 +12,6 @@ import (
 	"cmd/go/internal/modload"
 	"cmd/go/internal/str"
 	"context"
-	"errors"
 	"fmt"
 	"io/fs"
 	"os"
@@ -20,7 +19,7 @@ import (
 )
 
 var cmdUse = &base.Command{
-	UsageLine: "go work use [-r] [moddirs]",
+	UsageLine: "go work use [-r] moddirs",
 	Short:     "add modules to workspace file",
 	Long: `Use provides a command-line interface for adding
 directories, optionally recursively, to a go.work file.
@@ -33,6 +32,9 @@ The -r flag searches recursively for modules in the argument
 directories, and the use command operates as if each of the directories
 were specified as arguments: namely, use directives will be added for
 directories that exist, and removed for directories that do not exist.
+
+See the workspaces reference at https://go.dev/ref/mod#workspaces
+for more information.
 `,
 }
 
@@ -82,13 +84,14 @@ func runUse(ctx context.Context, cmd *base.Command, args []string) {
 	lookDir := func(dir string) {
 		absDir, dir := pathRel(workDir, dir)
 
-		fi, err := os.Stat(filepath.Join(absDir, "go.mod"))
+		fi, err := fsys.Stat(filepath.Join(absDir, "go.mod"))
 		if err != nil {
 			if os.IsNotExist(err) {
 				keepDirs[absDir] = ""
-				return
+			} else {
+				base.Errorf("go: %v", err)
 			}
-			base.Errorf("go: %v", err)
+			return
 		}
 
 		if !fi.Mode().IsRegular() {
@@ -101,14 +104,37 @@ func runUse(ctx context.Context, cmd *base.Command, args []string) {
 		keepDirs[absDir] = dir
 	}
 
+	if len(args) == 0 {
+		base.Fatalf("go: 'go work use' requires one or more directory arguments")
+	}
 	for _, useDir := range args {
+		absArg, _ := pathRel(workDir, useDir)
+
+		info, err := fsys.Stat(absArg)
+		if err != nil {
+			// Errors raised from os.Stat are formatted to be more user-friendly.
+			if os.IsNotExist(err) {
+				base.Errorf("go: directory %v does not exist", absArg)
+			} else {
+				base.Errorf("go: %v", err)
+			}
+			continue
+		} else if !info.IsDir() {
+			base.Errorf("go: %s is not a directory", absArg)
+			continue
+		}
+
 		if !*useR {
 			lookDir(useDir)
 			continue
 		}
 
 		// Add or remove entries for any subdirectories that still exist.
-		err := fsys.Walk(useDir, func(path string, info fs.FileInfo, err error) error {
+		fsys.Walk(useDir, func(path string, info fs.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+
 			if !info.IsDir() {
 				if info.Mode()&fs.ModeSymlink != 0 {
 					if target, err := fsys.Stat(path); err == nil && target.IsDir() {
@@ -120,13 +146,9 @@ func runUse(ctx context.Context, cmd *base.Command, args []string) {
 			lookDir(path)
 			return nil
 		})
-		if err != nil && !errors.Is(err, os.ErrNotExist) {
-			base.Errorf("go: %v", err)
-		}
 
 		// Remove entries for subdirectories that no longer exist.
 		// Because they don't exist, they will be skipped by Walk.
-		absArg, _ := pathRel(workDir, useDir)
 		for absDir, _ := range haveDirs {
 			if str.HasFilePathPrefix(absDir, absArg) {
 				if _, ok := keepDirs[absDir]; !ok {
@@ -186,5 +208,5 @@ func pathRel(workDir, dir string) (abs, canonical string) {
 
 	// Normalize relative paths to use slashes, so that checked-in go.work
 	// files with relative paths within the repo are platform-independent.
-	return abs, filepath.ToSlash(rel)
+	return abs, modload.ToDirectoryPath(rel)
 }

src/cmd/go/internal/workcmd/work.go

@@ -12,7 +12,7 @@ import (
 var CmdWork = &base.Command{
 	UsageLine: "go work",
 	Short:     "workspace maintenance",
-	Long: `Go workspace provides access to operations on workspaces.
+	Long: `Work provides access to operations on workspaces.
 
 Note that support for workspaces is built into many other commands, not
 just 'go work'.
@@ -20,6 +20,12 @@ just 'go work'.
 See 'go help modules' for information about Go's module system of which
 workspaces are a part.
 
+See https://go.dev/ref/mod#workspaces for an in-depth reference on
+workspaces.
+
+See https://go.dev/doc/tutorial/workspaces for an introductory
+tutorial on workspaces.
+
 A workspace is specified by a go.work file that specifies a set of
 module directories with the "use" directive. These modules are used as
 root modules by the go command for builds and related operations.  A

src/cmd/go/testdata/script/build_buildvcs_auto.txt

@@ -0,0 +1,87 @@
+# Regression test for https://go.dev/issue/51748: by default, 'go build' should
+# not attempt to stamp VCS information when the VCS tool is not present.
+
+[short] skip
+[!exec:git] skip
+
+cd sub
+exec git init .
+exec git add sub.go
+exec git commit -m 'initial state'
+cd ..
+
+exec git init
+exec git submodule add ./sub
+exec git add go.mod example.go
+exec git commit -m 'initial state'
+
+
+# Control case: with a git binary in $PATH,
+# 'go build' on a package in the same git repo
+# succeeds and stamps VCS metadata by default.
+
+go build -o example.exe .
+go version -m example.exe
+stdout '^\tbuild\tvcs=git$'
+stdout '^\tbuild\tvcs.modified=false$'
+
+
+# Building a binary from a different (nested) VCS repo should not stamp VCS
+# info. It should be an error if VCS stamps are requested explicitly with
+# '-buildvcs' (since we know the VCS metadata exists), but not an error
+# with '-buildvcs=auto'.
+
+go build -o sub.exe ./sub
+go version -m sub.exe
+! stdout '^\tbuild\tvcs'
+
+! go build -buildvcs -o sub.exe ./sub
+stderr '\Aerror obtaining VCS status: main package is in repository ".*" but current directory is in repository ".*"\n\tUse -buildvcs=false to disable VCS stamping.\n\z'
+
+cd ./sub
+go build -o sub.exe .
+go version -m sub.exe
+! stdout '^\tbuild\tvcs'
+
+! go build -buildvcs -o sub.exe .
+stderr '\Aerror obtaining VCS status: main module is in repository ".*" but current directory is in repository ".*"\n\tUse -buildvcs=false to disable VCS stamping.\n\z'
+cd ..
+
+
+# After removing 'git' from $PATH, 'go build -buildvcs' should fail...
+
+env PATH=
+env path=
+! go build -buildvcs -o example.exe .
+stderr 'go: missing Git command\. See https://golang\.org/s/gogetcmd$'
+
+# ...but by default we should omit VCS metadata when the tool is missing.
+
+go build -o example.exe .
+go version -m example.exe
+! stdout '^\tbuild\tvcs'
+
+# The default behavior can be explicitly set with '-buildvcs=auto'.
+
+go build -buildvcs=auto -o example.exe .
+go version -m example.exe
+! stdout '^\tbuild\tvcs'
+
+# Other flag values should be rejected with a useful error message.
+
+! go build -buildvcs=hg -o example.exe .
+stderr '\Ainvalid boolean value "hg" for -buildvcs: value is neither ''auto'' nor a valid bool\nusage: go build .*\nRun ''go help build'' for details.\n\z'
+
+
+-- go.mod --
+module example
+
+go 1.18
+-- example.go --
+package main
+
+func main() {}
+-- sub/sub.go --
+package main
+
+func main() {}