go/printer: parenthesize literal function types in conversions

Also: gofmt -w src misc

R=r
CC=golang-dev, iant
https://golang.org/cl/6591071

src/pkg/go/printer/nodes.go

@@ -791,7 +791,14 @@ func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
 		if len(x.Args) > 1 {
 			depth++
 		}
-		p.expr1(x.Fun, token.HighestPrec, depth)
+		if _, ok := x.Fun.(*ast.FuncType); ok {
+			// conversions to literal function types require parentheses around the type
+			p.print(token.LPAREN)
+			p.expr1(x.Fun, token.HighestPrec, depth)
+			p.print(token.RPAREN)
+		} else {
+			p.expr1(x.Fun, token.HighestPrec, depth)
+		}
 		p.print(x.Lparen, token.LPAREN)
 		if x.Ellipsis.IsValid() {
 			p.exprList(x.Lparen, x.Args, depth, 0, x.Ellipsis)

src/pkg/go/printer/testdata/expressions.golden

@@ -647,3 +647,18 @@ func _() {
 		a...,
 	)
 }
+
+// Literal function types in conversions must be parenthesized;
+// for now go/parser accepts the unparenthesized form where it
+// is non-ambiguous.
+func _() {
+	// these conversions should be rewritten to look
+	// the same as the parenthesized conversions below
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+}

src/pkg/go/printer/testdata/expressions.input

@@ -676,3 +676,18 @@ func _() {
 		a...,
 	)
 }
+
+// Literal function types in conversions must be parenthesized;
+// for now go/parser accepts the unparenthesized form where it
+// is non-ambiguous.
+func _() {
+	// these conversions should be rewritten to look
+	// the same as the parenthesized conversions below
+	_ = func()()(nil)
+	_ = func(x int)(float)(nil)
+	_ = func() func() func()()(nil)
+
+	_ = (func()())(nil)
+	_ = (func(x int)(float))(nil)
+	_ = (func() func() func()())(nil)
+}

src/pkg/go/printer/testdata/expressions.raw

@@ -647,3 +647,18 @@ func _() {
 		a...,
 	)
 }
+
+// Literal function types in conversions must be parenthesized;
+// for now go/parser accepts the unparenthesized form where it
+// is non-ambiguous.
+func _() {
+	// these conversions should be rewritten to look
+	// the same as the parenthesized conversions below
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+}

src/pkg/reflect/all_test.go

@@ -1494,7 +1494,7 @@ func TestMethod(t *testing.T) {
 	}
 
 	// Curried method of value.
-	tfunc := TypeOf(func(int) int(nil))
+	tfunc := TypeOf((func(int) int)(nil))
 	v := ValueOf(p).Method(1)
 	if tt := v.Type(); tt != tfunc {
 		t.Errorf("Value Method Type is %s; want %s", tt, tfunc)