gc: remove funarg special case in structfield

This should make CL 5431046 a little simpler.

R=ken2
CC=golang-dev
https://golang.org/cl/5444048

src/cmd/gc/dcl.c

@@ -771,7 +771,6 @@ structfield(Node *n)
 		break;
 	}
 
-	// tofunarg will undo this for _ arguments
 	if(n->left && n->left->op == ONAME) {
 		f->nname = n->left;
 		f->embedded = n->embedded;
@@ -840,13 +839,6 @@ tofunargs(NodeList *l)
 	for(tp = &t->type; l; l=l->next) {
 		f = structfield(l->n);
 
-		// Unlink the name for _ arguments.
-		if(l->n->left && l->n->left->op == ONAME && isblank(l->n->left)) {
-			f->nname = nil;
-			f->sym = nil;
-			f->embedded = 0;
-		}
-
 		// esc.c needs to find f given a PPARAM to add the tag.
 		if(l->n->left && l->n->left->class == PPARAM)
 			l->n->left->paramfld = f;

src/cmd/gc/subr.c

@@ -2226,13 +2226,12 @@ structargs(Type **tl, int mustname)
 	gen = 0;
 	for(t = structfirst(&savet, tl); t != T; t = structnext(&savet)) {
 		n = N;
-		if(t->sym)
-			n = newname(t->sym);
-		else if(mustname) {
-			// have to give it a name so we can refer to it in trampoline
+		if(mustname && (t->sym == nil || strcmp(t->sym->name, "_") == 0)) {
+			// invent a name so that we can refer to it in the trampoline
 			snprint(buf, sizeof buf, ".anon%d", gen++);
 			n = newname(lookup(buf));
-		}
+		} else if(t->sym)
+			n = newname(t->sym);
 		a = nod(ODCLFIELD, n, typenod(t->type));
 		a->isddd = t->isddd;
 		if(n != N)
@@ -2274,7 +2273,7 @@ genwrapper(Type *rcvr, Type *method, Sym *newnam, int iface)
 	int isddd;
 	Val v;
 
-	if(0 && debug['r'])
+	if(debug['r'])
 		print("genwrapper rcvrtype=%T method=%T newnam=%S\n",
 			rcvr, method, newnam);
 

src/cmd/gc/typecheck.c

@@ -2465,6 +2465,7 @@ static void
 domethod(Node *n)
 {
 	Node *nt;
+	Type *t;
 
 	nt = n->type->nname;
 	typecheck(&nt, Etype);
@@ -2474,6 +2475,20 @@ domethod(Node *n)
 		n->type->nod = N;
 		return;
 	}
+	
+	// If we have
+	//	type I interface {
+	//		M(_ int)
+	//	}
+	// then even though I.M looks like it doesn't care about the
+	// value of its argument, a specific implementation of I may
+	// care.  The _ would suppress the assignment to that argument
+	// while generating a call, so remove it.
+	for(t=getinargx(nt->type)->type; t; t=t->down) {
+		if(t->sym != nil && strcmp(t->sym->name, "_") == 0)
+			t->sym = nil;
+	}
+
 	*n->type = *nt->type;
 	n->type->nod = N;
 	checkwidth(n->type);

test/blank.go

@@ -101,6 +101,29 @@ func main() {
 	}
 
 	h(a, b)
+	
+	m()
+}
+
+type I interface {
+	M(_ int, y int)
+}
+
+type TI struct{}
+
+func (TI) M(x int, y int) {
+	if x != y {
+		println("invalid M call:", x, y)
+		panic("bad M")
+	}
+}
+
+func m() {
+	var i I
+	
+	i = TI{}
+	i.M(1, 1)
+	i.M(2, 2)
 }
 
 // useless but legal
@@ -120,3 +143,4 @@ func _() {
 func ff() {
 	var _ int = 1
 }
+