go/scanner: Use explicit scanner.Mode type.

R=r, bradfitz
CC=golang-dev
https://golang.org/cl/5574059

src/pkg/go/parser/parser.go

@@ -54,7 +54,7 @@ type parser struct {
 
 func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mode) {
 	p.file = fset.AddFile(filename, fset.Base(), len(src))
-	var m uint
+	var m scanner.Mode
 	if mode&ParseComments != 0 {
 		m = scanner.ScanComments
 	}

src/pkg/go/scanner/scanner.go

@@ -40,7 +40,7 @@ type Scanner struct {
 	dir  string       // directory portion of file.Name()
 	src  []byte       // source
 	err  ErrorHandler // error reporting; or nil
-	mode uint         // scanning mode
+	mode Mode         // scanning mode
 
 	// scanning state
 	ch         rune // current character
@@ -86,11 +86,13 @@ func (S *Scanner) next() {
 	}
 }
 
-// The mode parameter to the Init function is a set of flags (or 0).
+// A mode value is set of flags (or 0).
 // They control scanner behavior.
 //
+type Mode uint
+
 const (
-	ScanComments    = 1 << iota // return comments as COMMENT tokens
+	ScanComments    Mode = 1 << iota // return comments as COMMENT tokens
 	dontInsertSemis                  // do not automatically insert semicolons - for testing only
 )
 
@@ -109,7 +111,7 @@ const (
 // Note that Init may call err if there is an error in the first character
 // of the file.
 //
-func (S *Scanner) Init(file *token.File, src []byte, err ErrorHandler, mode uint) {
+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")

src/pkg/go/scanner/scanner_test.go

@@ -281,7 +281,7 @@ func TestScan(t *testing.T) {
 	}
 }
 
-func checkSemi(t *testing.T, line string, mode uint) {
+func checkSemi(t *testing.T, line string, mode Mode) {
 	var S Scanner
 	file := fset.AddFile("TestSemis", fset.Base(), len(line))
 	S.Init(file, []byte(line), nil, mode)