gofmt: test rewrite of (x.(type)) -> x.(type)

R=rsc
CC=golang-dev
https://golang.org/cl/6867062

src/cmd/gofmt/gofmt_test.go

@@ -84,6 +84,7 @@ var tests = []struct {
 	{"testdata/comments.input", ""},
 	{"testdata/import.input", ""},
 	{"testdata/crlf.input", ""},       // test case for issue 3961; see also TestCRLF
+	{"testdata/typeswitch.input", ""}, // test case for issue 4470
 }
 
 func TestRewrite(t *testing.T) {

src/cmd/gofmt/testdata/typeswitch.golden

@@ -0,0 +1,60 @@
+/*
+	Parenthesized type switch expressions originally
+	accepted by gofmt must continue to be rewritten
+	into the correct unparenthesized form.
+
+	Only type-switches that didn't declare a variable
+	in the the type switch type assertion and which
+	contained only "expression-like" (named) types in their
+	cases were permitted to have their type assertion parenthesized
+	by go/parser (due to a weak predicate in the parser). All others
+	were rejected always, either with a syntax error in the
+	type switch header or in the case.
+
+	See also issue 4470.
+*/
+package p
+
+func f() {
+	var x interface{}
+	switch x.(type) { // should remain the same
+	}
+	switch x.(type) { // should become: switch x.(type) {
+	}
+
+	switch x.(type) { // should remain the same
+	case int:
+	}
+	switch x.(type) { // should become: switch x.(type) {
+	case int:
+	}
+
+	switch x.(type) { // should remain the same
+	case []int:
+	}
+
+	// Parenthesized (x.(type)) in type switches containing cases
+	// with unnamed (literal) types were never permitted by gofmt;
+	// thus there won't be any code in the wild using this style if
+	// the code was gofmt-ed.
+	/*
+		switch (x.(type)) {
+		case []int:
+		}
+	*/
+
+	switch t := x.(type) { // should remain the same
+	default:
+		_ = t
+	}
+
+	// Parenthesized (x.(type)) in type switches declaring a variable
+	// were never permitted by gofmt; thus there won't be any code in
+	// the wild using this style if the code was gofmt-ed.
+	/*
+		switch t := (x.(type)) {
+		default:
+			_ = t
+		}
+	*/
+}

src/cmd/gofmt/testdata/typeswitch.input

@@ -0,0 +1,60 @@
+/*
+	Parenthesized type switch expressions originally
+	accepted by gofmt must continue to be rewritten
+	into the correct unparenthesized form.
+
+	Only type-switches that didn't declare a variable
+	in the the type switch type assertion and which
+	contained only "expression-like" (named) types in their
+	cases were permitted to have their type assertion parenthesized
+	by go/parser (due to a weak predicate in the parser). All others
+	were rejected always, either with a syntax error in the
+	type switch header or in the case.
+
+	See also issue 4470.
+*/
+package p
+
+func f() {
+	var x interface{}
+	switch x.(type) { // should remain the same
+	}
+	switch (x.(type)) { // should become: switch x.(type) {
+	}
+
+	switch x.(type) { // should remain the same
+	case int:
+	}
+	switch (x.(type)) { // should become: switch x.(type) {
+	case int:
+	}
+
+	switch x.(type) { // should remain the same
+	case []int:
+	}
+
+	// Parenthesized (x.(type)) in type switches containing cases
+	// with unnamed (literal) types were never permitted by gofmt;
+	// thus there won't be any code in the wild using this style if
+	// the code was gofmt-ed.
+	/*
+	switch (x.(type)) {
+	case []int:
+	}
+	*/
+
+	switch t := x.(type) { // should remain the same
+	default:
+		_ = t
+	}
+
+	// Parenthesized (x.(type)) in type switches declaring a variable
+	// were never permitted by gofmt; thus there won't be any code in
+	// the wild using this style if the code was gofmt-ed.
+	/*
+	switch t := (x.(type)) {
+	default:
+		_ = t
+	}
+	*/
+}