cmd/gc: record line number for auto-generated wrappers as <autogenerated>:1

Before we used line 1 of the first source file.
This should be clearer.

Fixes issue 4388.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://codereview.appspot.com/92250044

1 files changed, 50 insertions, 0 deletions

diff --git a/test/fixedbugs/issue4388.go b/test/fixedbugs/issue4388.go
new file mode 100644
index 000000000..c8c53b710
--- /dev/null
+++ b/test/fixedbugs/issue4388.go
@@ -0,0 +1,50 @@
+// run
+
+// Copyright 2014 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 (
+	"fmt"
+	"io"
+	"runtime"
+)
+
+type T struct {
+	io.Closer
+}
+
+func f1() {
+	// The 4 here and below depends on the number of internal runtime frames
+	// that sit between a deferred function called during panic and
+	// the original frame. If that changes, this test will start failing and
+	// the number here will need to be updated.
+	defer checkLine(4)
+	var t *T
+	var c io.Closer = t
+	c.Close()
+}
+
+func f2() {
+	defer checkLine(4)
+	var t T
+	var c io.Closer = t
+	c.Close()
+}
+
+func main() {
+	f1()
+	f2()
+}
+
+func checkLine(n int) {
+	if err := recover(); err == nil {
+		panic("did not panic")
+	}
+	_, file, line, _ := runtime.Caller(n)
+	if file != "<autogenerated>" || line != 1 {
+		panic(fmt.Sprintf("expected <autogenerated>:1 have %s:%d", file, line))
+	}
+}