gh-141510: Change repr(frozendict) for empty dict (#144921)

repr(frozendict()) returns "frozendict()" instead of
"frozendict({})".

Author: vstinner

Lib/test/test_dict.py

@@ -1767,6 +1767,9 @@ def test_update(self):
         self.assertEqual(copy, frozendict({'x': 1}))
 
     def test_repr(self):
+        d = frozendict()
+        self.assertEqual(repr(d), "frozendict()")
+
         d = frozendict(x=1, y=2)
         self.assertEqual(repr(d), "frozendict({'x': 1, 'y': 2})")
 

Objects/dictobject.c

@@ -7868,6 +7868,11 @@ static PyMethodDef frozendict_methods[] = {
 static PyObject *
 frozendict_repr(PyObject *self)
 {
+    PyDictObject *mp = _PyAnyDict_CAST(self);
+    if (mp->ma_used == 0) {
+        return PyUnicode_FromFormat("%s()", Py_TYPE(self)->tp_name);
+    }
+
     PyObject *repr = anydict_repr_impl(self);
     if (repr == NULL) {
         return NULL;