cmd/compile: ignore carriage return in magic comments

Update #11771.

Change-Id: I3bb3262619765d3ca79652817e17e8f260f41907
Reviewed-on: https://go-review.googlesource.com/12379
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/lex.go

@@ -1576,7 +1576,7 @@ func getlinepragma() int {
 		}
 		cp = nil
 
-		text := lexbuf.String()
+		text := strings.TrimSuffix(lexbuf.String(), "\r")
 
 		if strings.HasPrefix(text, "go:cgo_") {
 			pragcgo(text)
@@ -1666,7 +1666,7 @@ func getlinepragma() int {
 	if linep == 0 {
 		return c
 	}
-	text := lexbuf.String()
+	text := strings.TrimSuffix(lexbuf.String(), "\r")
 	n := 0
 	for _, c := range text[linep:] {
 		if c < '0' || c > '9' {

test/fixedbugs/issue11771.go

@@ -0,0 +1,64 @@
+// +build !nacl
+// run
+
+// Copyright 2015 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.
+
+// Issue 11771: Magic comments should ignore carriage returns.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+)
+
+func main() {
+	if runtime.Compiler != "gc" {
+		return
+	}
+
+	dir, err := ioutil.TempDir("", "go-issue11771")
+	if err != nil {
+		log.Fatalf("creating temp dir: %v\n", err)
+	}
+	defer os.RemoveAll(dir)
+
+	// The go:nowritebarrier magic comment is only permitted in
+	// the runtime package.  So we confirm that the compilation
+	// fails.
+
+	var buf bytes.Buffer
+	fmt.Fprintln(&buf, `
+package main
+
+func main() {
+}
+`)
+	fmt.Fprintln(&buf, "//go:nowritebarrier\r")
+	fmt.Fprintln(&buf, `
+func x() {
+}
+`)
+
+	if err := ioutil.WriteFile(filepath.Join(dir, "x.go"), buf.Bytes(), 0666); err != nil {
+		log.Fatal(err)
+	}
+
+	cmd := exec.Command("go", "tool", "compile", "x.go")
+	cmd.Dir = dir
+	output, err := cmd.CombinedOutput()
+	if err == nil {
+		log.Fatal("compile succeeded unexpectedly")
+	}
+	if !bytes.Contains(output, []byte("only allowed in runtime")) {
+		log.Fatalf("wrong error message from compiler; got:\n%s\n", output)
+	}
+}