gen: implement `thread.str()` (#10820)

vlib/v/gen/c/auto_str_methods.v

@@ -172,6 +172,9 @@ fn (mut g Gen) gen_str_for_type(typ ast.Type) string {
 			ast.Chan {
 				g.gen_str_for_chan(sym.info, styp, str_fn_name)
 			}
+			ast.Thread {
+				g.gen_str_for_thread(sym.info, styp, str_fn_name)
+			}
 			else {
 				verror("could not generate string method $str_fn_name for type '$styp'")
 			}
@@ -467,6 +470,12 @@ fn (mut g Gen) gen_str_for_chan(info ast.Chan, styp string, str_fn_name string)
 	g.auto_str_funcs.writeln('static string ${str_fn_name}($styp x) { return sync__Channel_auto_str(x, _SLIT("$elem_type_name")); }')
 }
 
+fn (mut g Gen) gen_str_for_thread(info ast.Thread, styp string, str_fn_name string) {
+	ret_type_name := util.strip_main_name(g.table.get_type_name(info.return_type))
+	g.type_definitions.writeln('static string ${str_fn_name}($styp _); // auto}')
+	g.auto_str_funcs.writeln('static string ${str_fn_name}($styp _) { return _SLIT("thread($ret_type_name)");}')
+}
+
 [inline]
 fn styp_to_str_fn_name(styp string) string {
 	return styp.replace_each(['*', '', '.', '__', ' ', '__']) + '_str'

vlib/v/tests/thread_to_string_test.v

@@ -0,0 +1,8 @@
+fn ret_ten() int {
+	return 10
+}
+
+fn test_thread_str() {
+	th := go ret_ten()
+	assert th.str() == 'thread(int)'
+}