checker: fixes resolution sum type with an alias type

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

vlib/v/ast/table.v

@@ -1280,15 +1280,15 @@ pub fn (t &Table) sumtype_has_variant(parent Type, variant Type, is_as bool) boo
 	if parent_sym.kind == .sum_type {
 		parent_info := parent_sym.info as SumType
 		var_sym := t.sym(variant)
-		if var_sym.kind == .aggregate {
-			var_info := var_sym.info as Aggregate
-			for var_type in var_info.types {
-				if !t.sumtype_has_variant(parent, var_type, is_as) {
-					return false
+		match var_sym.kind {
+			.aggregate {
+				return t.sumtype_check_aggregate_variant(parent, var_sym.info as Aggregate,
+					is_as)
 			}
+			.alias {
+				return t.sumtype_check_alias_variant(parent, var_sym.info as Alias, is_as)
 			}
-			return true
-		} else {
+			else {
 				for v in parent_info.variants {
 					if v.idx() == variant.idx() && (!is_as || v.nr_muls() == variant.nr_muls()) {
 						return true
@@ -1296,9 +1296,23 @@ pub fn (t &Table) sumtype_has_variant(parent Type, variant Type, is_as bool) boo
 				}
 			}
 		}
+	}
 	return false
 }
 
+fn (t &Table) sumtype_check_aggregate_variant(parent_type Type, aggregate_sym &Aggregate, is_as bool) bool {
+	for var_type in aggregate_sym.types {
+		if !t.sumtype_has_variant(parent_type, var_type, is_as) {
+			return false
+		}
+	}
+	return true
+}
+
+fn (t &Table) sumtype_check_alias_variant(parent_type Type, alias_info &Alias, is_as bool) bool {
+	return alias_info.parent_type == parent_type
+}
+
 pub fn (t &Table) is_sumtype_or_in_variant(parent Type, typ Type) bool {
 	if typ == 0 {
 		return false

vlib/v/tests/known_errors/testdata/cast_aliases_on_generics_type.vv

@@ -1,8 +1,6 @@
 type ParseRes = Result<[]Token, ParseErr>
 
-struct ParseErr{
-
-}
+struct ParseErr {}
 
 type Opt<T> = None<T> | Some<T>
 
@@ -26,7 +24,7 @@ fn test_report() {
 	r := Opt<ParseRes>(None<ParseRes>{})
 	match r {
 		Some<ParseRes> {
-			rx := Result<[]Token, ParseErr>(r)
+			rx := Result<[]Token, ParseErr>(r.value)
 		}
 		None<ParseRes> {}
 	}