Add comments about mypy limitation regarding TypeVar constraints

Author: not-my-profile

stdlib/builtins.pyi

@@ -725,6 +725,8 @@ class memoryview(Sized, Sequence[int]):
 @final
 class bool(int):
     def __new__(cls: type[Self], __o: object = ...) -> Self: ...
+    # The following overloads could be represented more elegantly with a TypeVar("_B", bool, int),
+    # however mypy has a bug regarding TypeVar constraints (https://github.com/python/mypy/issues/11880).
     @overload
     def __and__(self, __x: bool) -> bool: ...
     @overload

stdlib/re.pyi

@@ -51,6 +51,11 @@ if sys.version_info < (3, 7):
     # undocumented
     _pattern_type: type
 
+# Type-wise these overloads are unnecessary, they could also be modeled using
+# unions in the parameter types. However mypy has a bug regarding TypeVar
+# constraints (https://github.com/python/mypy/issues/11880),
+# which limits us here because AnyStr is a constrained TypeVar.
+
 @overload
 def compile(pattern: AnyStr, flags: _FlagsType = ...) -> Pattern[AnyStr]: ...
 @overload