cmd/gc: fix method values whose receiver is an unnamed interface.

Fixes #6140.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/13083043

src/cmd/gc/closure.c

@@ -285,6 +285,8 @@ makepartialcall(Node *fn, Type *t0, Node *meth)
 	NodeList *body, *l, *callargs, *retargs;
 	char *p;
 	Sym *sym;
+	Pkg *spkg;
+	static Pkg* gopkg;
 	int i, ddd;
 
 	// TODO: names are not right
@@ -296,10 +298,18 @@ makepartialcall(Node *fn, Type *t0, Node *meth)
 	basetype = rcvrtype;
 	if(isptr[rcvrtype->etype])
 		basetype = basetype->type;
-	if(basetype->sym == S)
+	if(basetype->etype != TINTER && basetype->sym == S)
 		fatal("missing base type for %T", rcvrtype);
 
-	sym = pkglookup(p, basetype->sym->pkg);
+	spkg = nil;
+	if(basetype->sym != S)
+		spkg = basetype->sym->pkg;
+	if(spkg == nil) {
+		if(gopkg == nil)
+			gopkg = mkpkg(strlit("go"));
+		spkg = gopkg;
+	}
+	sym = pkglookup(p, spkg);
 	free(p);
 	if(sym->flags & SymUniq)
 		return sym->def;

test/fixedbugs/issue6140.go

+// compile
+
+// 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.
+
+// Issue 6140: compiler incorrectly rejects method values
+// whose receiver has an unnamed interface type.
+
+package p
+
+type T *interface {
+	m() int
+}
+
+var x T
+
+var _ = (*x).m
+
+var y interface {
+	m() int
+}
+
+var _ = y.m
+
+type I interface {
+	String() string
+}
+
+var z *struct{ I }
+var _ = z.String

test/method2.go

@@ -21,7 +21,7 @@ func (p *P1) val() int { return 1 } // ERROR "receiver.* pointer|invalid pointer
 type I interface{}
 type I1 interface{}
 
-func (p I) val() int { return 1 } // ERROR "receiver.*interface|invalid pointer or interface receiver"
+func (p I) val() int   { return 1 } // ERROR "receiver.*interface|invalid pointer or interface receiver"
 func (p *I1) val() int { return 1 } // ERROR "receiver.*interface|invalid pointer or interface receiver"
 
 type Val interface {
@@ -33,4 +33,5 @@ var _ = (*Val).val // ERROR "method"
 var v Val
 var pv = &v
 
-var _ = pv.val()	// ERROR "method"
+var _ = pv.val() // ERROR "method"
+var _ = pv.val   // ERROR "method"