cgen: add support for alias map keys (#16682)

vlib/v/gen/c/cgen.v

@@ -3064,6 +3064,10 @@ fn (mut g Gen) map_fn_ptrs(key_typ ast.TypeSymbol) (string, string, string, stri
 	mut clone_fn := ''
 	mut free_fn := '&map_free_nop'
 	match key_typ.kind {
+		.alias {
+			alias_key_type := (key_typ.info as ast.Alias).parent_type
+			return g.map_fn_ptrs(g.table.sym(alias_key_type))
+		}
 		.u8, .i8, .char {
 			hash_fn = '&map_hash_int_1'
 			key_eq_fn = '&map_eq_int_1'

vlib/v/tests/map_key_alias_test.v

@@ -0,0 +1,16 @@
+type String = string
+type Rune = rune
+
+fn test_map_key_alias() {
+	mut str_data := map[string]map[String]string{}
+	str_data['str'][String('String')] = 'test'
+	assert '${str_data}' == "{'str': {'String': 'test'}}"
+
+	mut i32_data := map[i32]string{}
+	i32_data[23] = 'num'
+	assert '${i32_data}' == "{23: 'num'}"
+
+	mut rune_data := map[Rune]string{}
+	rune_data[`A`] = 'rune'
+	assert '${rune_data}' == "{`A`: 'rune'}"
+}