cmd/gc: fix incorrect error when using f(g()) form on ... args

Fixes #5358.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/11282044

src/cmd/gc/typecheck.c

@@ -2131,9 +2131,9 @@ typecheckaste(int op, Node *call, int isddd, Type *tstruct, NodeList *nl, char *
 				for(; tn; tn=tn->down) {
 					if(assignop(tn->type, tl->type->type, &why) == 0) {
 						if(call != N)
-							yyerror("cannot use %T as type %T in argument to %N%s", tn->type, tl->type, call, why);
+							yyerror("cannot use %T as type %T in argument to %N%s", tn->type, tl->type->type, call, why);
 						else
-							yyerror("cannot use %T as type %T in %s%s", tn->type, tl->type, desc, why);
+							yyerror("cannot use %T as type %T in %s%s", tn->type, tl->type->type, desc, why);
 					}
 				}
 				goto out;

test/fixedbugs/issue5358.go

+// errorcheck
+
+// 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 5358: incorrect error message when using f(g()) form on ... args.
+
+package main
+
+func f(x int, y ...int) {}
+
+func g() (int, []int)
+
+func main() {
+	f(g()) // ERROR "as type int in"
+}