go/scanner: remove some code

R=r
CC=golang-dev
https://golang.org/cl/4550077

src/pkg/go/scanner/scanner.go

@@ -22,6 +22,7 @@ package scanner
 
 import (
 	"bytes"
+	"fmt"
 	"go/token"
 	"path/filepath"
 	"strconv"
@@ -134,36 +135,6 @@ func (S *Scanner) Init(file *token.File, src []byte, err ErrorHandler, mode uint
 }
 
 
-func charString(ch int) string {
-	var s string
-	switch ch {
-	case -1:
-		return `EOF`
-	case '\a':
-		s = `\a`
-	case '\b':
-		s = `\b`
-	case '\f':
-		s = `\f`
-	case '\n':
-		s = `\n`
-	case '\r':
-		s = `\r`
-	case '\t':
-		s = `\t`
-	case '\v':
-		s = `\v`
-	case '\\':
-		s = `\\`
-	case '\'':
-		s = `\'`
-	default:
-		s = string(ch)
-	}
-	return "'" + s + "' (U+" + strconv.Itob(ch, 16) + ")"
-}
-
-
 func (S *Scanner) error(offs int, msg string) {
 	if S.err != nil {
 		S.err.Error(S.file.Position(S.file.Pos(offs)), msg)
@@ -700,7 +671,7 @@ scanAgain:
 			tok = S.switch3(token.OR, token.OR_ASSIGN, '|', token.LOR)
 		default:
 			if S.mode&AllowIllegalChars == 0 {
-				S.error(offs, "illegal character "+charString(ch))
+				S.error(offs, fmt.Sprintf("illegal character '%c' (%U)", ch, ch))
 			}
 			insertSemi = S.insertSemi // preserve insertSemi info
 		}

src/pkg/go/scanner/scanner_test.go

@@ -650,7 +650,8 @@ var errors = []struct {
 	pos int
 	err string
 }{
-	{`#`, token.ILLEGAL, 0, "illegal character '#' (U+23)"},
+	{"\a", token.ILLEGAL, 0, "illegal character '\a' (U+0007)"},
+	{`#`, token.ILLEGAL, 0, "illegal character '#' (U+0023)"},
 	{`' '`, token.CHAR, 0, ""},
 	{`''`, token.CHAR, 0, "illegal character literal"},
 	{`'\8'`, token.CHAR, 2, "unknown escape sequence"},