- Parse expressions as opposed to statements for gofmt rewrite patterns.

Allows stand-alone types (e.g. []int as patterns) and doesn't require
a semicolon at the end (which are now mandatory terminators).

- Fix a matcher bug.

R=rsc
CC=golang-dev
https://golang.org/cl/179088

src/cmd/gofmt/rewrite.go

@@ -37,21 +37,12 @@ func initRewrite() {
 // but there are problems with preserving formatting and also
 // with what a wildcard for a statement looks like.
 func parseExpr(s string, what string) ast.Expr {
-	stmts, err := parser.ParseStmtList("input", s)
+	x, err := parser.ParseExpr("input", s)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "parsing %s %s: %s\n", what, s, err)
 		os.Exit(2)
 	}
-	if len(stmts) != 1 {
+	return x
-		fmt.Fprintf(os.Stderr, "%s must be single expression\n", what)
-		os.Exit(2)
-	}
-	x, ok := stmts[0].(*ast.ExprStmt)
-	if !ok {
-		fmt.Fprintf(os.Stderr, "%s must be single expression\n", what)
-		os.Exit(2)
-	}
-	return x.X
 }
 
 
@@ -147,6 +138,9 @@ func match(m map[string]reflect.Value, pattern, val reflect.Value) bool {
 	switch p := p.(type) {
 	case *reflect.SliceValue:
 		v := v.(*reflect.SliceValue)
+		if p.Len() != v.Len() {
+			return false
+		}
 		for i := 0; i < p.Len(); i++ {
 			if !match(m, p.Elem(i), v.Elem(i)) {
 				return false
@@ -156,6 +150,9 @@ func match(m map[string]reflect.Value, pattern, val reflect.Value) bool {
 
 	case *reflect.StructValue:
 		v := v.(*reflect.StructValue)
+		if p.NumField() != v.NumField() {
+			return false
+		}
 		for i := 0; i < p.NumField(); i++ {
 			if !match(m, p.Field(i), v.Field(i)) {
 				return false