PEP-718: Indicate that the (lenient) mypy patch is up-to-date (#5195)

* Indicate that the (lenient) mypy patch is up-to-date

* Link directly to PRs in note about experimental status

Author: gvanrossum

peps/pep-0718.rst

@@ -839,22 +839,21 @@ Reference Implementation
   branch. It predates ``types.FunctionGenericAlias`` (it returns a plain
   ``types.GenericAlias``) and does not yet cover ``MethodWrapperType``.
 * `python/mypy#21880 <https://github.com/python/mypy/pull/21880>`__: a type checker
-  prototype of the behaviour specified here, behind
-  ``--enable-incomplete-feature=SubscriptableFunctions``. It confirmed that
-  ``ParamSpec``, ``TypeVarTuple`` and type parameter defaults can follow the rules for
-  generic classes by reusing the same code, and implements the overload filtering
-  described above.
+  prototype behind ``--enable-incomplete-feature=SubscriptableFunctions``.
+  It implements function subscription, including overload filtering, method
+  binding, type parameter defaults, ``ParamSpec`` and ``TypeVarTuple`` support,
+  and the Python 3.16 version check.
 * `python/mypy#21881 <https://github.com/python/mypy/pull/21881>`__: a variant of the
   prototype that only allows subscripting callables traceable to a ``def`` (see
   `Rejected Ideas`_). It cannot be fully sound either, since type checkers have to
   assume that decorators preserve the kind of object they wrap.
 
-The following rules are not yet implemented in either prototype: reporting unsolvable
-type parameters at the call instead of the definition, not reporting overloads that
-differ only in type parameter bounds as overlapping, the consistency rule for overload
-implementations, the Python version check, and keeping return-only type parameters
-through ``ParamSpec`` decorators (mypy currently solves them to ``Never``, so a
-``contextmanager`` function like ``session`` above cannot be subscripted).
+The prototypes are experimental. The mypy prototype in
+`python/mypy#21880 <https://github.com/python/mypy/pull/21880>`__
+has been updated to address the typing rules specified here, with regression
+tests. The stricter variant in
+`python/mypy#21881 <https://github.com/python/mypy/pull/21881>`__
+has not received these updates. The cpython prototype has not yet been updated.
 
 Rejected Ideas
 --------------