go/parser: ParseExpr must accept type expressions

My old code was trying to be too smart.
Also: Slightly better error message format
for gofmt -r pattern errors.

Fixes issue 4406.

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/8267045

4 files changed, 23 insertions, 2 deletions

diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index 8ff00a253..75a322a6c 100644
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -84,6 +84,7 @@ var tests = []struct {
 	{"testdata/rewrite5.input", "-r=x+x->2*x"},
 	{"testdata/rewrite6.input", "-r=fun(x)->Fun(x)"},
 	{"testdata/rewrite7.input", "-r=fun(x...)->Fun(x)"},
+	{"testdata/rewrite8.input", "-r=interface{}->int"},
 	{"testdata/stdin*.input", "-stdin"},
 	{"testdata/comments.input", ""},
 	{"testdata/import.input", ""},
diff --git a/src/cmd/gofmt/rewrite.go b/src/cmd/gofmt/rewrite.go
index 1aa1f6ed0..66d2331a5 100644
--- a/src/cmd/gofmt/rewrite.go
+++ b/src/cmd/gofmt/rewrite.go
@@ -35,10 +35,10 @@ func initRewrite() {
 // It might make sense to expand this to allow statement patterns,
 // 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 {
+func parseExpr(s, what string) ast.Expr {
 	x, err := parser.ParseExpr(s)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "parsing %s %s: %s\n", what, s, err)
+		fmt.Fprintf(os.Stderr, "parsing %s %s at %s\n", what, s, err)
 		os.Exit(2)
 	}
 	return x
diff --git a/src/cmd/gofmt/testdata/rewrite8.golden b/src/cmd/gofmt/testdata/rewrite8.golden
new file mode 100644
index 000000000..cfc452b03
--- /dev/null
+++ b/src/cmd/gofmt/testdata/rewrite8.golden
@@ -0,0 +1,10 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Check that literal type expression rewrites are accepted.
+// Was issue 4406.
+
+package p
+
+type T int
diff --git a/src/cmd/gofmt/testdata/rewrite8.input b/src/cmd/gofmt/testdata/rewrite8.input
new file mode 100644
index 000000000..235efa91c
--- /dev/null
+++ b/src/cmd/gofmt/testdata/rewrite8.input
@@ -0,0 +1,10 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Check that literal type expression rewrites are accepted.
+// Was issue 4406.
+
+package p
+
+type T interface{}