[ty] Validate free type variables in ClassVar annotations

[charliermarsh]

Summary

We now reject ClassVar annotations whose types contain free type variables hidden by aliases or captured in protocol members and TypedDict fields. We also allow Self in generic classes and type variables bound by a nested callable's own signature.

from typing import ClassVar

type Items[T] = list[T]

class Container[T]:
    values: ClassVar[Items[T]]  # Error: ClassVar cannot contain type variables

The traversal expands alias values so unused arguments and arguments erased by specialization do not cause errors. It tracks callable bindings and treats type-variable bounds and defaults as metadata.

We follow finite recursive specializations, including cases where a protocol member or TypedDict field exposes a variable only after the first specialization. The shared recursion analysis distinguishes fixed outer variables from captures whose binding definitions also participate in the recursion. Occurrences beyond growing or unresolved recursive references can still remain undiagnosed; an incomplete search does not produce an error.

We reuse completed searches under the same callable bindings to avoid repeatedly traversing shared types, such as those in Pydantic's CoreSchema. An incomplete recursive search cannot supply a cached result.

Builds on #29155.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 98.24%. The percentage of expected errors that received a diagnostic held steady at 98.24%. The number of fully passing files held steady at 134/146.

[astral-sh-bot]

Memory usage report

Summary

Project	Old	New	Diff	Outcome
prefect	475.10MB	475.11MB	+0.00% (14.84kB)	⏫
sphinx	172.45MB	172.45MB	+0.00% (1.09kB)	⏫
flake8	38.28MB	38.28MB	-	✅
trio	92.58MB	92.58MB	-	✅

Significant changes

Click to expand detailed breakdown

prefect

Name	Old	New	Diff	Outcome
infer_definition_types	37.83MB	37.83MB	+0.01% (5.44kB)	⏫
ProtocolInterface	909.11kB	910.94kB	+0.20% (1.84kB)	⏫
place_by_id	4.11MB	4.11MB	+0.03% (1.28kB)	⏫
code_generator_of_static_class	392.98kB	393.98kB	+0.26% (1.01kB)	⏫
model_config	113.21kB	114.22kB	+0.89% (1.01kB)	⏫
cached_protocol_interface	304.07kB	304.96kB	+0.29% (912.00B)	⏫
CallableType	8.94MB	8.94MB	+0.01% (696.00B)	⏫
PropertyInstanceType	177.44kB	177.84kB	+0.22% (408.00B)	⏫
function_known_decorators	1.82MB	1.82MB	+0.01% (244.00B)	⏫
infer_deferred_types	4.81MB	4.81MB	+0.00% (236.00B)	⏫
remove_self_inner::interned_arguments	256.57kB	256.78kB	+0.08% (216.00B)	⏫
place_by_id::interned_arguments	2.94MB	2.94MB	+0.01% (216.00B)	⏫
GenericAlias<'db>::try_mro_	4.54MB	4.54MB	+0.00% (216.00B)	⏫
Type<'db>::apply_specialization_inner_	2.96MB	2.96MB	-0.01% (192.00B)	⬇️
GenericContext	2.27MB	2.27MB	+0.01% (156.00B)	⏫
...			22 more

sphinx

Name	Old	New	Diff	Outcome
infer_definition_types	11.71MB	11.72MB	+0.01% (1.06kB)	⏫
infer_scope_types_impl	6.20MB	6.20MB	+0.00% (32.00B)	⏫

[astral-sh-bot]

ecosystem-analyzer results

Lint rule	Added	Removed	Changed
invalid-type-form	0	2	0
Total	0	2	0

Flaky changes detected. This PR summary excludes flaky changes; see the HTML report for details.

Raw diff:

discord.py (https://github.com/Rapptz/discord.py)
- discord/ui/action_row.py:122:36 error[invalid-type-form] `ClassVar` cannot contain type variables
- discord/ui/container.py:109:35 error[invalid-type-form] `ClassVar` cannot contain type variables

Full report with detailed diff (timing results)