cmd/compile/internal/gc: use new AST parser

Introduce a new noder type to transform package syntax's AST into gc's
Node tree. Hidden behind a new -newparser flag.

Change-Id: Id0e862ef6196c41533876afc4ec289e21d422d18

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

@@ -29,6 +29,8 @@ var (
 	goarch  string
 	goroot  string
 	buildid string
+
+	flag_newparser bool
 )
 
 var (
@@ -182,6 +184,7 @@ func Main() {
 	obj.Flagcount("live", "debug liveness analysis", &debuglive)
 	obj.Flagcount("m", "print optimization decisions", &Debug['m'])
 	flag.BoolVar(&flag_msan, "msan", false, "build code compatible with C/C++ memory sanitizer")
+	flag.BoolVar(&flag_newparser, "newparser", false, "use new parser")
 	flag.BoolVar(&newexport, "newexport", true, "use new export format") // TODO(gri) remove eventually (issue 15323)
 	flag.BoolVar(&nolocalimports, "nolocalimports", false, "reject local (relative) imports")
 	flag.StringVar(&outfile, "o", "", "write output to `file`")
@@ -311,25 +314,14 @@ func Main() {
 		}
 
 		linehistpush(infile)
-
-		f, err := os.Open(infile)
-		if err != nil {
-			fmt.Printf("open %s: %v\n", infile, err)
-			errorexit()
-		}
-		bin := bufio.NewReader(f)
-
-		// Skip initial BOM if present.
-		if r, _, _ := bin.ReadRune(); r != BOM {
-			bin.UnreadRune()
-		}
-
 		block = 1
 		iota_ = -1000000
-
 		imported_unsafe = false
-
-		parse_file(bin)
+		if flag_newparser {
+			parseFile(infile)
+		} else {
+			oldParseFile(infile)
+		}
 		if nsyntaxerrors != 0 {
 			errorexit()
 		}
@@ -338,9 +330,7 @@ func Main() {
 		// for the line history to work, and which then has to be corrected elsewhere,
 		// just add a line here.
 		lexlineno++
-
 		linehistpop()
-		f.Close()
 	}
 
 	testdclstack()

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

@@ -15,6 +15,7 @@ package gc
 import (
 	"bufio"
 	"fmt"
+	"os"
 	"strconv"
 	"strings"
 )
@@ -26,8 +27,20 @@ func parse_import(bin *bufio.Reader, indent []byte) {
 	newparser(bin, indent).import_package()
 }
 
-// parse_file parses a single Go source file.
-func parse_file(bin *bufio.Reader) {
+// oldParseFile parses a single Go source file.
+func oldParseFile(infile string) {
+	f, err := os.Open(infile)
+	if err != nil {
+		fmt.Printf("open %s: %v\n", infile, err)
+		errorexit()
+	}
+	defer f.Close()
+	bin := bufio.NewReader(f)
+
+	// Skip initial BOM if present.
+	if r, _, _ := bin.ReadRune(); r != BOM {
+		bin.UnreadRune()
+	}
 	newparser(bin, nil).file()
 }