compiler: Initialize named returns to default values

Make them behave as locals. We must initialize them at the start
because the default value could also be used inside the function body.

Signed-off-by: Evgenii Stratonikov <fyfyrchik@runbox.com>

pkg/compiler/return_test.go

@@ -120,6 +120,19 @@ func TestNamedReturn(t *testing.T) {
 	t.Run("AnotherVariable", runCase("b, c", big.NewInt(5)))
 }
 
+func TestNamedReturnDefault(t *testing.T) {
+	src := `package foo
+	func Main() int {
+		a, b, c := f()
+		return a + b + c
+	}
+	func f() (_ int, b int, c int) {
+		b += 1
+		return
+	}`
+	eval(t, src, big.NewInt(1))
+}
+
 func TestTypeAssertReturn(t *testing.T) {
 	src := `
 		package main