cmd/cgo: retain original file paths in godefs generated comment

Don't rewrite relative file paths to absolute file paths in the
godefs generated code comment.

Fixes #52063

Change-Id: Ie9c5bd021b8f3954e827838930861622c7aa90b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/396936
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testgodefs/testgodefs_test.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 )
@@ -58,9 +59,32 @@ func TestGoDefs(t *testing.T) {
 			t.Fatalf("%s: %v\n%s", strings.Join(cmd.Args, " "), err, cmd.Stderr)
 		}
 
-		if err := os.WriteFile(filepath.Join(dir, fp+"_defs.go"), out, 0644); err != nil {
+		fn := fp + "_defs.go"
+		if err := os.WriteFile(filepath.Join(dir, fn), out, 0644); err != nil {
 			t.Fatal(err)
 		}
+
+		// Verify that command line arguments are not rewritten in the generated comment,
+		// see go.dev/issue/52063
+		hasGeneratedByComment := false
+		for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+			cgoExe := "cgo"
+			if runtime.GOOS == "windows" {
+				cgoExe = "cgo.exe"
+			}
+			if !strings.HasPrefix(line, "// "+cgoExe+" -godefs") {
+				continue
+			}
+			if want := "// " + cgoExe + " " + strings.Join(cmd.Args[3:], " "); line != want {
+				t.Errorf("%s: got generated comment %q, want %q", fn, line, want)
+			}
+			hasGeneratedByComment = true
+			break
+		}
+
+		if !hasGeneratedByComment {
+			t.Errorf("%s: comment with generating cgo -godefs command not found", fn)
+		}
 	}
 
 	main, err := os.ReadFile(filepath.Join("testdata", "main.go"))

src/cmd/cgo/godefs.go

@@ -16,11 +16,11 @@ import (
 )
 
 // godefs returns the output for -godefs mode.
-func (p *Package) godefs(f *File) string {
+func (p *Package) godefs(f *File, args []string) string {
 	var buf bytes.Buffer
 
 	fmt.Fprintf(&buf, "// Code generated by cmd/cgo -godefs; DO NOT EDIT.\n")
-	fmt.Fprintf(&buf, "// %s %s\n", filepath.Base(os.Args[0]), strings.Join(os.Args[1:], " "))
+	fmt.Fprintf(&buf, "// %s %s\n", filepath.Base(args[0]), strings.Join(args[1:], " "))
 	fmt.Fprintf(&buf, "\n")
 
 	override := make(map[string]string)

src/cmd/cgo/main.go

@@ -291,6 +291,10 @@ func main() {
 		usage()
 	}
 
+	// Save original command line arguments for the godefs generated comment. Relative file
+	// paths in os.Args will be rewritten to absolute file paths in the loop below.
+	osArgs := make([]string, len(os.Args))
+	copy(osArgs, os.Args[:])
 	goFiles := args[i:]
 
 	for _, arg := range args[:i] {
@@ -390,7 +394,7 @@ func main() {
 		p.PackagePath = f.Package
 		p.Record(f)
 		if *godefs {
-			os.Stdout.WriteString(p.godefs(f))
+			os.Stdout.WriteString(p.godefs(f, osArgs))
 		} else {
 			p.writeOutput(f, input)
 		}