New flags for gofmt:

- oldparser            parse old syntax (required semicolons)
- oldprinter           print old syntax (required semicolons)

By default, these flags are enabled for now.
Setting -oldparser=false has no effect until go/parser is changed
to accept the new syntax.

Enabled exp/parser in Makefile; update dependent exp/eval.

R=rsc
https://golang.org/cl/174051

src/cmd/gofmt/doc.go

@@ -29,6 +29,14 @@ The flags are:
 	-tabwidth=8
 		tab width in spaces.
 
+Flags to aid the transition to the new semicolon-free syntax (these flags will be
+removed eventually):
+
+	-oldparser=true
+		parse old syntax (required semicolons).
+	-oldprinter=true
+		print old syntax (required semicolons).
+
 Debugging flags:
 
 	-trace

src/cmd/gofmt/gofmt.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"bytes";
+	oldParser "exp/parser";
 	"flag";
 	"fmt";
 	"go/ast";
@@ -30,9 +31,13 @@ var (
 	trace		= flag.Bool("trace", false, "print parse trace");
 
 	// layout control
-	tabwidth	= flag.Int("tabwidth", 8, "tab width");
-	tabindent	= flag.Bool("tabindent", false, "indent with tabs independent of -spaces");
-	usespaces	= flag.Bool("spaces", false, "align with spaces instead of tabs");
+	tabWidth	= flag.Int("tabwidth", 8, "tab width");
+	tabIndent	= flag.Bool("tabindent", false, "indent with tabs independent of -spaces");
+	useSpaces	= flag.Bool("spaces", false, "align with spaces instead of tabs");
+
+	// semicolon transition
+	useOldParser	= flag.Bool("oldparser", true, "parse old syntax (required semicolons)");
+	useOldPrinter	= flag.Bool("oldprinter", true, "print old syntax (required semicolons)");
 )
 
 
@@ -69,13 +74,16 @@ func initParserMode() {
 
 
 func initPrinterMode() {
-	printerMode = uint(0);
-	if *tabindent {
+	printerMode = printer.NoStringConcat;
+	if *tabIndent {
 		printerMode |= printer.TabIndent
 	}
-	if *usespaces {
+	if *useSpaces {
 		printerMode |= printer.UseSpaces
 	}
+	if !*useOldPrinter {
+		printerMode |= printer.NoSemis
+	}
 }
 
 
@@ -91,7 +99,12 @@ func processFile(f *os.File) os.Error {
 		return err
 	}
 
-	file, err := parser.ParseFile(f.Name(), src, parserMode);
+	var file *ast.File;
+	if *useOldParser {
+		file, err = oldParser.ParseFile(f.Name(), src, parserMode)
+	} else {
+		file, err = parser.ParseFile(f.Name(), src, parserMode)
+	}
 	if err != nil {
 		return err
 	}
@@ -101,7 +114,7 @@ func processFile(f *os.File) os.Error {
 	}
 
 	var res bytes.Buffer;
-	_, err = (&printer.Config{printerMode, *tabwidth, nil}).Fprint(&res, file);
+	_, err = (&printer.Config{printerMode, *tabWidth, nil}).Fprint(&res, file);
 	if err != nil {
 		return err
 	}
@@ -176,8 +189,8 @@ func walkDir(path string) {
 func main() {
 	flag.Usage = usage;
 	flag.Parse();
-	if *tabwidth < 0 {
-		fmt.Fprintf(os.Stderr, "negative tabwidth %d\n", *tabwidth);
+	if *tabWidth < 0 {
+		fmt.Fprintf(os.Stderr, "negative tabwidth %d\n", *tabWidth);
 		os.Exit(2);
 	}
 

src/pkg/Makefile

@@ -55,6 +55,7 @@ DIRS=\
 	exp/eval\
 	exp/exception\
 	exp/iterable\
+	exp/parser\
 	expvar\
 	flag\
 	fmt\

src/pkg/exp/eval/world.go

@@ -9,7 +9,7 @@ package eval
 
 import (
 	"go/ast";
-	"go/parser";
+	parser "exp/parser";
 	"go/scanner";
 	"go/token";
 	"os";