Fix changelog entry and __mutable_keys__ tracking for PEP 705 (#334)

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 - Add support for PEP 742, adding `typing_extensions.TypeIs`. Patch
   by Jelle Zijlstra.
-- Drop runtime error when a mutable `TypedDict` key overrides a read-only
+- Drop runtime error when a read-only `TypedDict` item overrides a mutable
   one. Type checkers should still flag this as an error. Patch by Jelle
   Zijlstra.
 - Speedup `issubclass()` checks against simple runtime-checkable protocols by

src/test_typing_extensions.py

@@ -4147,9 +4147,15 @@ def test_make_mutable_key_readonly(self):
         class Base(TypedDict):
             a: int
 
+        self.assertEqual(Base.__readonly_keys__, frozenset())
+        self.assertEqual(Base.__mutable_keys__, frozenset({'a'}))
+
         class Child(Base):
             a: ReadOnly[int]  # type checker error, but allowed at runtime
 
+        self.assertEqual(Child.__readonly_keys__, frozenset({'a'}))
+        self.assertEqual(Child.__mutable_keys__, frozenset())
+
     def test_can_make_readonly_key_mutable(self):
         class Base(TypedDict):
             a: ReadOnly[int]

src/typing_extensions.py

@@ -943,6 +943,7 @@ def __new__(cls, name, bases, ns, *, total=True):
                 else:
                     optional_keys.add(annotation_key)
                 if ReadOnly in qualifiers:
+                    mutable_keys.discard(annotation_key)
                     readonly_keys.add(annotation_key)
                 else:
                     mutable_keys.add(annotation_key)