func f() (int, int);

x := f();

used to give
	fatal error: dowidth fn struct struct { int; int }

now gives
	assignment count mismatch: 1 = 2

R=ken
OCL=27198
CL=27201

src/cmd/gc/walk.c

@@ -3067,6 +3067,41 @@ colas(Node *nl, Node *nr)
 	n = N;
 	cr = listcount(nr);
 	cl = listcount(nl);
+
+	/* check calls early, to give better message for a := f() */
+	if(cr == 1) {
+		switch(nr->op) {
+		case OCALLMETH:
+		case OCALLINTER:
+		case OCALL:
+			walktype(nr->left, Erv);
+			convlit(nr->left, types[TFUNC]);
+			t = nr->left->type;
+			if(t == T)
+				return;	// error already printed
+			if(t->etype == tptr)
+				t = t->type;
+			if(t == T || t->etype != TFUNC) {
+				yyerror("cannot call %T", t);
+				return;
+			}
+			if(t->outtuple != cl) {
+				cr = t->outtuple;
+				goto badt;
+			}
+			// finish call - first half above
+			l = listfirst(&savel, &nl);
+			t = structfirst(&saver, getoutarg(t));
+			while(l != N) {
+				a = old2new(l, t->type);
+				n = list(n, a);
+				l = listnext(&savel);
+				t = structnext(&saver);
+			}
+			n = rev(n);
+			return n;
+		}
+	}
 	if(cl != cr) {
 		if(cr == 1)
 			goto multi;
@@ -3099,29 +3134,6 @@ multi:
 	default:
 		goto badt;
 
-	case OCALLMETH:
-	case OCALLINTER:
-	case OCALL:
-		walktype(nr->left, Erv);
-		convlit(nr->left, types[TFUNC]);
-		t = nr->left->type;
-		if(t != T && t->etype == tptr)
-			t = t->type;
-		if(t == T || t->etype != TFUNC)
-			goto badt;
-		if(t->outtuple != cl)
-			goto badt;
-
-		l = listfirst(&savel, &nl);
-		t = structfirst(&saver, getoutarg(t));
-		while(l != N) {
-			a = old2new(l, t->type);
-			n = list(n, a);
-			l = listnext(&savel);
-			t = structnext(&saver);
-		}
-		break;
-
 	case OINDEX:
 		// check if rhs is a map index.
 		// if so, types are valuetype,bool

test/golden.out

@@ -145,8 +145,6 @@ fixedbugs/bug035.go:7: variable f redeclared in this block
 
 =========== fixedbugs/bug037.go
 fixedbugs/bug037.go:6: vlong: undefined
-fixedbugs/bug037.go:6: illegal types for operand: AS
-	undefined
 
 =========== fixedbugs/bug039.go
 fixedbugs/bug039.go:6: variable x redeclared in this block
@@ -219,7 +217,11 @@ fixedbugs/bug091.go:15: illegal types for operand: AS
 M
 
 =========== fixedbugs/bug103.go
+fixedbugs/bug103.go:8: assignment count mismatch: 1 = 0
+fixedbugs/bug103.go:8: x: undefined
 fixedbugs/bug103.go:8: function requires a return type
+fixedbugs/bug103.go:8: illegal types for operand: AS
+	int
 
 =========== fixedbugs/bug113.go
 main.I is int, not int32