[ty] Reject generic metaclasses parameterized by type variables#23628
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AlexWaygood merged 3 commits intomainfrom Feb 28, 2026
Merged
[ty] Reject generic metaclasses parameterized by type variables#23628AlexWaygood merged 3 commits intomainfrom
AlexWaygood merged 3 commits intomainfrom
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Generic metaclasses are not supported per the typing spec. This adds a check that rejects `metaclass=SomeGeneric[T]` with an `invalid-metaclass` error when the metaclass argument is a parameterized generic class. https://claude.ai/code/session_01Nhdsupjg85NjKVFHSTZR9x
…ble parameters Generic metaclasses parameterized by type variables are not supported per the typing spec. `metaclass=Meta[int]` (fully specialized) is fine, but `metaclass=Meta[T]` (parameterized by type variables) is not. This adds a check in `try_metaclass` that detects when the explicit metaclass is a `GenericAlias` whose specialization contains type variables, and emits an `invalid-metaclass` diagnostic. https://claude.ai/code/session_01Nhdsupjg85NjKVFHSTZR9x
Typing conformance results improved 🎉The percentage of diagnostics emitted that were expected errors increased from 85.38% to 85.39%. The percentage of expected errors that received a diagnostic increased from 75.92% to 76.01%. Summary
True positives addedDetails
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Memory usage reportMemory usage unchanged ✅ |
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| Lint rule | Added | Removed | Changed |
|---|---|---|---|
invalid-argument-type |
0 | 1 | 0 |
| Total | 0 | 1 | 0 |
charliermarsh
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Feb 28, 2026
carljm
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Mar 2, 2026
* main: [ty] Move binary expression logic out of `builder.rs` (#23649) [ty] Limit recursion depth when displaying self-referential function types (#23647) [ty] Move comparison logic out of `builder.rs` (#23646) Avoid inserting redundant `None` elements in UP045 (#23459) [ty] Add more ParamSpec validation for `P.args` and `P.kwargs` (#23640) [ty] Sync vendored typeshed stubs (#23642) [ty] Fix inference of `t.__mro__` if `t` is an instance of `type[Any]` (#23632) [ty] Detect inconsistent generic base class specializations (#23615) [ty] Validate type variable defaults don't reference later type parameters or type parameters out of scope (#23623) [ty] Ban nested `Required`/`NotRequired`, and ban them both outside of `TypedDict` fields (#23627) [ty] Reject generic metaclasses parameterized by type variables (#23628) Update default Python version examples (#23605) fix binops with NewType of float and Unknown (#23620) [ty] Reject functions with PEP-695 type parameters that shadow type parameters from enclosing scopes (#23619) [ty] Reject ellipsis literals in odd places in type/annotation expressions (#23611) [ty] hash-cons `UseDefMap` fields (#23283)
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Summary
Add validation to reject generic metaclasses that are parameterized by type variables, as these are banned by the typing spec.
Test Plan
mdtests