cmd/compile: correctly parse //line filename:line where filename contains ':'

This was a regression from 1.7. See the issue for details.

Fixes #18149.

Change-Id: Ic8f5a35d14edf9254b1275400316cff7aff32a27
Reviewed-on: https://go-review.googlesource.com/33799
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1022,13 +1022,14 @@ func (p *noder) error(err error) {
 func (p *noder) pragma(pos, line int, text string) syntax.Pragma {
 	switch {
 	case strings.HasPrefix(text, "line "):
-		i := strings.IndexByte(text, ':')
+		// Want to use LastIndexByte below but it's not defined in Go1.4 and bootstrap fails.
+		i := strings.LastIndex(text, ":") // look from right (Windows filenames may contain ':')
 		if i < 0 {
 			break
 		}
 		n, err := strconv.Atoi(text[i+1:])
 		if err != nil {
-			// todo: make this an error instead? it is almost certainly a bug.
+			// TODO: make this an error instead? it is almost certainly a bug.
 			break
 		}
 		if n > 1e8 {

test/fixedbugs/issue18149.go

@@ -0,0 +1,33 @@
+// run
+
+// Copyright 2016 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.
+
+// Verify that //line directives with filenames
+// containing ':' (Windows) are correctly parsed.
+// (For a related issue, see test/fixedbugs/bug305.go)
+
+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func check(file string, line int) {
+	_, f, l, ok := runtime.Caller(1)
+	if !ok {
+		panic("runtime.Caller(1) failed")
+	}
+	if f != file || l != line {
+		panic(fmt.Sprintf("got %s:%d; want %s:%d", f, l, file, line))
+	}
+}
+
+func main() {
+//line /foo/bar.go:123
+	check(`/foo/bar.go`, 123)
+//line c:/foo/bar.go:987
+	check(`c:/foo/bar.go`, 987)
+}