channel types parsed not according to spec by 6g

R=r, rsc
CC=golang-dev
https://golang.org/cl/193101

test/bugs/bug249.go

@@ -0,0 +1,39 @@
+// errchk $G $D/$F.go
+
+// Copyright 2009 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.
+
+package main
+
+var c1 chan<- chan int
+var c2 chan<- (chan int) // same type as c1 according to gccgo, gofmt
+var c3 chan (<-chan int) // same type as c1 according to 6g
+
+func main() {
+	c1 = c2 // this should be ok, bug 6g doesn't accept it
+	c1 = c3 // ERROR "chan"
+}
+
+/*
+Channel types are parsed differently by 6g then by gccgo and gofmt.
+The channel type specification ( http://golang.org/doc/go_spec.html#Channel_types )
+says that a channel type is either
+
+	chan ElementType
+	chan <- ElementType
+	<-chan ElementType
+
+which indicates that the <- binds to the chan token (not to the ElementType).
+So:
+
+chan <- chan int
+
+should be parsed as
+
+chan<- (chan int)
+
+Both gccgo and gofmt adhere to this, while 6g parses this as
+
+chan (<-chan int)
+*/

test/golden.out

@@ -154,3 +154,10 @@ BUG: tuple evaluation order
 bugs/bug246.go:17: cannot convert 0 to type unsafe.Pointer
 bugs/bug246.go:17: cannot convert 0 (type uintptr) to type *int in conversion
 BUG: bug246
+
+=========== bugs/bug249.go
+BUG: errchk: bugs/bug249.go:15: missing expected error: 'chan'
+errchk: bugs/bug249.go: unmatched error messages:
+==================================================
+bugs/bug249.go:14: cannot use c2 (type chan<- (chan int)) as type chan <-chan int in assignment
+==================================================