compiler: calculate local variables properly

In case when right-hand side of an assignment is a function,
left-hand side should be used.

pkg/compiler/func_scope.go

@@ -124,7 +124,7 @@ func (c *funcScope) countLocals() int {
 			}
 		case *ast.AssignStmt:
 			if n.Tok == token.DEFINE {
-				size += len(n.Rhs)
+				size += len(n.Lhs)
 			}
 		case *ast.ReturnStmt, *ast.IfStmt:
 			size++

pkg/compiler/global_test.go

@@ -38,6 +38,18 @@ func TestMultiDeclaration(t *testing.T) {
 	eval(t, src, big.NewInt(6))
 }
 
+func TestCountLocal(t *testing.T) {
+	src := `package foo
+	func Main() int {
+		a, b, c, d := f()
+		return a + b + c + d
+	}
+	func f() (int, int, int, int) {
+		return 1, 2, 3, 4
+	}`
+	eval(t, src, big.NewInt(10))
+}
+
 func TestMultiDeclarationLocal(t *testing.T) {
 	src := `package foo
 	func Main() int {