From 4112509618ee88519f899be20efc6882496b57c8 Mon Sep 17 00:00:00 2001
From: Davis Goodin <dagood@microsoft.com>
Date: Mon, 23 Jan 2023 16:51:51 -0800
Subject: [PATCH] windows/mkwinsyscall: write source to temp file if formatting
 fails

This change writes the unformatted Go source code to a temp file if
"format.Source" fails. Print the temp file path to the console to make
it easy to find. The source code is what causes formatting errors, and
it can be difficult to diagnose them without this context.

Fixes golang/go#57925

Change-Id: Ifa4d8a6e8bc5006357b0bc88afce5ba1d6fe0a48
Reviewed-on: https://go-review.googlesource.com/c/sys/+/463216
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
---
 windows/mkwinsyscall/mkwinsyscall.go | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/windows/mkwinsyscall/mkwinsyscall.go b/windows/mkwinsyscall/mkwinsyscall.go
index 7fe4efa9..11f4873b 100644
--- a/windows/mkwinsyscall/mkwinsyscall.go
+++ b/windows/mkwinsyscall/mkwinsyscall.go
@@ -871,6 +871,22 @@ func (src *Source) Generate(w io.Writer) error {
 	return nil
 }
 
+func writeTempSourceFile(data []byte) (string, error) {
+	f, err := os.CreateTemp("", "mkwinsyscall-generated-*.go")
+	if err != nil {
+		return "", err
+	}
+	_, err = f.Write(data)
+	if closeErr := f.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		os.Remove(f.Name()) // best effort
+		return "", err
+	}
+	return f.Name(), nil
+}
+
 func usage() {
 	fmt.Fprintf(os.Stderr, "usage: mkwinsyscall [flags] [path ...]\n")
 	flag.PrintDefaults()
@@ -897,7 +913,12 @@ func main() {
 
 	data, err := format.Source(buf.Bytes())
 	if err != nil {
-		log.Fatal(err)
+		log.Printf("failed to format source: %v", err)
+		f, err := writeTempSourceFile(buf.Bytes())
+		if err != nil {
+			log.Fatalf("failed to write unformatted source to file: %v", err)
+		}
+		log.Fatalf("for diagnosis, wrote unformatted source to %v", f)
 	}
 	if *filename == "" {
 		_, err = os.Stdout.Write(data)