From 726a6821417698218b17d3e37ced80eb551a0581 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Mon, 21 Oct 2024 06:33:19 -0300
Subject: [PATCH] checker: fix `T.unaliased_typ` if branch evaluation (fix
 #22587) (#22598)

---
 vlib/v/checker/comptime.v                     | 28 ++++++---
 .../comptime/comptime_unaliased_typ_test.v    | 63 +++++++++++++++++++
 2 files changed, 83 insertions(+), 8 deletions(-)
 create mode 100644 vlib/v/tests/comptime/comptime_unaliased_typ_test.v

diff --git a/vlib/v/checker/comptime.v b/vlib/v/checker/comptime.v
index fdd9cc772..cbbccb886 100644
--- a/vlib/v/checker/comptime.v
+++ b/vlib/v/checker/comptime.v
@@ -787,14 +787,26 @@ fn (mut c Checker) comptime_if_cond(mut cond ast.Expr, pos token.Pos) ComptimeBr
 					} else if cond.left in [ast.Ident, ast.SelectorExpr, ast.TypeNode] {
 						// `$if method.type is string`
 						c.expr(mut cond.left)
-						if cond.left is ast.SelectorExpr
-							&& c.comptime.is_comptime_selector_type(cond.left)
-							&& mut cond.right is ast.ComptimeType {
-							checked_type := c.comptime.get_comptime_var_type(cond.left)
-							return if c.comptime.is_comptime_type(checked_type, cond.right) {
-								.eval
-							} else {
-								.skip
+						if mut cond.left is ast.SelectorExpr && cond.right is ast.ComptimeType {
+							comptime_type := cond.right as ast.ComptimeType
+							if c.comptime.is_comptime_selector_type(cond.left) {
+								checked_type := c.comptime.get_comptime_var_type(cond.left)
+								return if c.comptime.is_comptime_type(checked_type, comptime_type) {
+									.eval
+								} else {
+									.skip
+								}
+							} else if cond.left.gkind_field == .unaliased_typ
+								&& cond.left.name_type != 0 {
+								// T.unaliased_typ
+								checked_type := c.unwrap_generic(cond.left.name_type)
+								return if c.comptime.is_comptime_type(c.table.unaliased_type(checked_type),
+									comptime_type)
+								{
+									.eval
+								} else {
+									.skip
+								}
 							}
 						}
 						return .unknown
diff --git a/vlib/v/tests/comptime/comptime_unaliased_typ_test.v b/vlib/v/tests/comptime/comptime_unaliased_typ_test.v
new file mode 100644
index 000000000..c91c7414b
--- /dev/null
+++ b/vlib/v/tests/comptime/comptime_unaliased_typ_test.v
@@ -0,0 +1,63 @@
+type StringAlias = string
+type BoolAlias = bool
+type IntAlias = int
+
+struct Decoder {
+	json string
+}
+
+pub fn decode[T](val string) !T {
+	mut decoder := Decoder{
+		json: val
+	}
+
+	mut result := T{}
+	decoder.decode_value(mut result)!
+	return result
+}
+
+fn (mut decoder Decoder) decode_value[T](mut val T) ! {
+	$if T.unaliased_typ is string {
+	} $else $if T.unaliased_typ in [$int, $float, $enum] {
+		bytes := unsafe { decoder.json.str.vbytes(decoder.json.len) }
+		unsafe {
+			string_buffer_to_generic_number(mut val, bytes)
+		}
+	} $else {
+		return error('cannot encode value with ${typeof(val).name} type')
+	}
+}
+
+@[direct_array_access; unsafe]
+pub fn string_buffer_to_generic_number[T](mut result T, data []u8) {
+	$if T is $option {
+	} $else $if T.unaliased_typ is string {
+		panic('should not happens')
+	} $else $if T.unaliased_typ is $int {
+		mut is_negative := false
+		for ch in data {
+			if ch == `-` {
+				is_negative = true
+				continue
+			}
+			digit := T(ch - `0`)
+			result = T(*result * 10 + digit)
+		}
+		if is_negative {
+			result *= -1
+		}
+	} $else {
+		panic('unsupported type ${typeof[T]().name}')
+	}
+}
+
+fn test_main() {
+	value := '1234567890123456789'
+	_ := decode[int](value)!
+	_ := decode[IntAlias](value)!
+	_ := decode[StringAlias]('"abcd"')!
+	_ := decode[int](value)!
+	_ := decode[string]('"abcd"')!
+
+	assert true
+}
-- 
2.39.5