checker,markused: add identification for sumtype.type_name() call (fix #23732) (#23739)

vlib/v/ast/table.v

@@ -28,6 +28,7 @@ pub mut:
 	arr_reverse      bool            // arr.reverse()
 	arr_init         bool            // [1, 2, 3]
 	arr_map          bool            // []map[key]value
+	type_name        bool            // var.type_name()
 	map_update       bool            // {...foo}
 	interpolation    bool            // '${foo} ${bar}'
 	option_or_result bool            // has panic call

vlib/v/checker/fn.v

@@ -1988,6 +1988,7 @@ fn (mut c Checker) method_call(mut node ast.CallExpr, mut continue_check &bool)
 	}
 	if left_sym.kind in [.sum_type, .interface] {
 		if method_name == 'type_name' {
+			c.table.used_features.type_name = true
 			return ast.string_type
 		}
 		if method_name == 'type_idx' {

vlib/v/markused/markused.v

@@ -212,6 +212,9 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 			core_fns << '__print_assert_failure'
 			core_fns << 'isnil'
 		}
+		if table.used_features.type_name {
+			core_fns << charptr_idx_str + '.vstring_literal'
+		}
 		if pref_.trace_calls || pref_.trace_fns.len > 0 {
 			include_panic_deps = true
 			core_fns << 'vgettid'

vlib/v/tests/skip_unused/sumtype_type_name.run.out

@@ -0,0 +1,2 @@
+Dbv
+string

vlib/v/tests/skip_unused/sumtype_type_name.skip_unused.run.out

@@ -0,0 +1,2 @@
+Dbv
+string

vlib/v/tests/skip_unused/sumtype_type_name.vv

@@ -0,0 +1,9 @@
+module main
+
+type Dbv = int | string
+
+fn main() {
+	mut m := Dbv('foo')
+	println(typeof(m).name)
+	println(m.type_name())
+}