Decide the fate of `type_params` in `_eval_type` and `_evaluate`

[sobolevn]

Feature or enhancement

Currently there are two places in our typing-related code that raise a DeprecationWarning when type_params parameter is not provided:

cpython/Lib/typing.py

Lines 432 to 442 in 07183eb

	def _eval_type(t, globalns, localns, type_params=_sentinel, *, recursive_guard=frozenset(),
	format=None, owner=None):
	"""Evaluate all forward references in the given type t.
	For use of globalns and localns see the docstring for get_type_hints().
	recursive_guard is used to prevent infinite recursion with a recursive
	ForwardRef.
	"""
	if type_params is _sentinel:
	_deprecation_warning_for_no_type_params_passed("typing._eval_type")
	type_params = ()

cpython/Lib/annotationlib.py

Lines 213 to 221 in 07183eb

	def _evaluate(self, globalns, localns, type_params=_sentinel, *, recursive_guard):
	import typing
	import warnings
	if type_params is _sentinel:
	typing._deprecation_warning_for_no_type_params_passed(
	"typing.ForwardRef._evaluate"
	)
	type_params = ()

The error message of this function says that the behavior will change in 3.15 to disallow this:

cpython/Lib/typing.py

Lines 410 to 420 in 07183eb

	def _deprecation_warning_for_no_type_params_passed(funcname: str) -> None:
	import warnings
	depr_message = (
	f"Failing to pass a value to the 'type_params' parameter "
	f"of {funcname!r} is deprecated, as it leads to incorrect behaviour "
	f"when calling {funcname} on a stringified annotation "
	f"that references a PEP 695 type parameter. "
	f"It will be disallowed in Python 3.15."
	)
	warnings.warn(depr_message, category=DeprecationWarning, stacklevel=3)

So, we have several options:

1. Adding TypeError('type_params parameter is not provided') when type_params is _sentinel
2. Changing type_params to not contain a default value
3. Do nothing?

CC @JelleZijlstra @AlexWaygood

I would like to work on this after we decide the fate of these functions :)

Linked PRs

• gh-136021: Make type_params a required parameter for typing._eval_type #136332
• gh-136021: Remove dead code for internal sentinel in typing #138120

[JelleZijlstra]

I find this whole deprecation somewhat pedantic. Most users won't need type_params; it's only needed in rare cases where using forward references to PEP 695 type params. It feels far too hand-holdy, especially for a private function.

That said, for _eval_type all internal callers pass in type_params already, so let's make the parameter required.

ForwardRef._evaluate is only there as a compatibility shim to be removed in Python 3.16, and it unconditionally raises DeprecationWarning. Let's keep the parameter optional so users don't have to worry about another deprecation within the deprecation.

[sobolevn]

Done! Thank you!