gc: Preserve original blank name for .anon substitution on out params.

Fixes #1802.

R=rsc
CC=golang-dev
https://golang.org/cl/5364043

src/cmd/gc/dcl.c

@@ -573,7 +573,7 @@ funchdr(Node *n)
 static void
 funcargs(Node *nt)
 {
-	Node *n;
+	Node *n, *nn;
 	NodeList *l;
 	int gen;
 
@@ -615,6 +615,10 @@ funcargs(Node *nt)
 			n->left->ntype = n->right;
 			if(isblank(n->left)) {
 				// Give it a name so we can assign to it during return.
+				// preserve the original in ->orig
+				nn = nod(OXXX, N, N);
+				*nn = *n->left;
+				n->left = nn;
 				snprint(namebuf, sizeof(namebuf), ".anon%d", gen++);
 				n->left->sym = lookup(namebuf);
 			}
@@ -1342,6 +1346,3 @@ funccompile(Node *n, int isclosure)
 	funcdepth = 0;
 	dclcontext = PEXTERN;
 }
-
-
-

src/cmd/gc/fmt.c

@@ -542,6 +542,7 @@ static int
 typefmt(Fmt *fp, Type *t)
 {
 	Type *t1;
+	Sym *s;
 
 	if(t == T)
 		return fmtstrcpy(fp, "<T>");
@@ -680,10 +681,23 @@ typefmt(Fmt *fp, Type *t)
 
 	case TFIELD:
 		if(!(fp->flags&FmtShort)) {
-			if(t->sym != S && !t->embedded)
-				fmtprint(fp, "%hS ", t->sym);
-			if((!t->sym || t->embedded) && fmtmode == FExp)
+			s = t->sym;
+			switch(fmtmode) {
+			case FErr:
+			case FExp:
+				// Take the name from the original, lest we substituted it with .anon%d
+				if (t->nname)
+					s = t->nname->orig->sym;
+
+				if((s == S || t->embedded)) {
 					fmtstrcpy(fp, "? ");
+					break;
+				}
+				// fallthrough
+			default:
+				if(!(s == S || t->embedded))
+					fmtprint(fp, "%hS ", s);
+			}
 		}
 
 		if(t->isddd)

test/fixedbugs/bug377.dir/one.go

+package one
+
+func Foo() (n int64, _ *int) {
+	return 42, nil
+}
+

test/fixedbugs/bug377.dir/two.go

+package two
+
+import _ "./one"
+

test/fixedbugs/bug377.go

+// $G $D/$F.dir/one.go && $G $D/$F.dir/two.go
+
+// Copyright 2011 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 1802
+
+ignored