cmd/gc: increase specificity of errors in function call context

Fixes #7129

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/86470044

src/cmd/gc/typecheck.c

@@ -310,7 +310,7 @@ typecheck1(Node **np, int top)
 	int ok, ntop;
 	Type *t, *tp, *missing, *have, *badtype;
 	Val v;
-	char *why;
+	char *why, *desc, descbuf[64];
 	
 	n = *np;
 
@@ -1139,7 +1139,11 @@ reswitch:
 			}
 			break;
 		}
-		typecheckaste(OCALL, n->left, n->isddd, getinargx(t), n->list, "function argument");
+		if(snprint(descbuf, sizeof descbuf, "argument to %N", n->left) < sizeof descbuf)
+			desc = descbuf;
+		else
+			desc = "function argument";
+		typecheckaste(OCALL, n->left, n->isddd, getinargx(t), n->list, desc);
 		ok |= Etop;
 		if(t->outtuple == 0)
 			goto ret;

test/fixedbugs/issue7129.go

+// errorcheck
+
+// Copyright 2014 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 7129: inconsistent "wrong arg type" error for multivalued g in f(g())
+
+package main
+
+func f(int) {}
+
+func g() bool { return true }
+
+func h(int, int) {}
+
+func main() {
+	f(g())        // ERROR "in argument to f"
+	f(true)       // ERROR "in argument to f"
+	h(true, true) // ERROR "in argument to h"
+}