go/scanner: better panic diagnostic

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5787045

diff --git a/src/pkg/go/scanner/scanner.go b/src/pkg/go/scanner/scanner.go
index 2395363b0ec88afb2b07b827113dd623f0ad02ba..da508747a6d4c668189d20593e021becabe459d2 100644 (file)
--- a/src/pkg/go/scanner/scanner.go
+++ b/src/pkg/go/scanner/scanner.go
@@ -109,7 +109,7 @@ const (
 func (s *Scanner) Init(file *token.File, src []byte, err ErrorHandler, mode Mode) {
        // Explicitly initialize all fields since a scanner may be reused.
        if file.Size() != len(src) {
-               panic("file size does not match src len")
+               panic(fmt.Sprintf("file size (%d) does not match src len (%d)", file.Size(), len(src)))
        }
        s.file = file
        s.dir, _ = filepath.Split(file.Name())