Report error when type alias has multiple TypeVarTuples (PEP 695) #20554
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When defining a type alias using the PEP 695 syntax with multiple TypeVarTuple-based type parameters (e.g., `type TA[*Ts1, *Ts2] = ...`), mypy now reports an error at definition time rather than only when the alias is used. This is consistent with how mypy handles classes with multiple TypeVarTuples and matches the behavior of other type checkers like pyright and pyrefly. Fixes python#20544.
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Could you support old-style type aliases too? The linked issue has that too, simply uncomment it. |
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A5rocks
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Jan 13, 2026
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CI failures look like it's because |
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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Report error when type alias has multiple TypeVarTuples (PEP 695)
When defining a type alias using the PEP 695 syntax with multiple TypeVarTuple-based type parameters (e.g.,
type TA[*Ts1, *Ts2] = ...), mypy now reports an error at definition time rather than only when the alias is used.This is consistent with how mypy handles classes with multiple TypeVarTuples and matches the behavior of other type checkers like pyright and pyrefly.
Fixes #20544.