From 8a1e90fff1b33b8f9fffe54b1e0db8f2da6997bc Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sun, 19 Feb 2023 13:56:14 -0300
Subject: [PATCH] checker: allow `none` to be casted to all option types,
 including aliases (#17348)

---
 vlib/v/checker/checker.v                |  4 ++-
 vlib/v/tests/cast_none_to_option_test.v | 38 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/cast_none_to_option_test.v

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index d5ff9b21cb..c3674b2c44 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2755,7 +2755,9 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 	if from_type == ast.void_type {
 		c.error('expression does not return a value so it cannot be cast', node.expr.pos())
 	}
-	if to_sym.kind == .sum_type {
+	if to_type.has_flag(.option) && from_type == ast.none_type {
+		// allow conversion from none to every option type
+	} else if to_sym.kind == .sum_type {
 		if from_type in [ast.int_literal_type, ast.float_literal_type] {
 			xx := if from_type == ast.int_literal_type { ast.int_type } else { ast.f64_type }
 			node.expr_type = c.promote_num(node.expr_type, xx)
diff --git a/vlib/v/tests/cast_none_to_option_test.v b/vlib/v/tests/cast_none_to_option_test.v
new file mode 100644
index 0000000000..a6768315f4
--- /dev/null
+++ b/vlib/v/tests/cast_none_to_option_test.v
@@ -0,0 +1,38 @@
+struct Test {}
+
+type AliasType = Test
+
+type I20 = int
+
+type Byt = u8
+
+fn test_cast_none() {
+	a := ?I20(none)
+	assert a == none
+	b := ?int(none)
+	assert b == none
+	c := ?i16(none)
+	assert c == none
+	d := ?u32(none)
+	assert d == none
+	e := ?u16(none)
+	assert e == none
+	f := ?u8(none)
+	assert f == none
+	g := ?Test(none)
+	assert g == none
+	h := ?AliasType(none)
+	assert h == none
+	i := ?Byt(none)
+	assert i == none
+	j := ?rune(none)
+	assert j == none
+	k := ?string(none)
+	assert k == none
+	l := ?[]Byt(none)
+	assert l == none
+	m := ?[]Test(none)
+	assert m == none
+	n := ?[]AliasType(none)
+	assert n == none
+}