Preserve class tparams when binding a classmethod to a callable#3599
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fangyi-zhou wants to merge 2 commits into
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Preserve class tparams when binding a classmethod to a callable#3599fangyi-zhou wants to merge 2 commits into
fangyi-zhou wants to merge 2 commits into
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Converting a generic classmethod reference like `Cls.method` to a callable went through `bind_boundmethod`, which always asked `bind_bound_method_type` to instantiate the method's tparams. When those tparams referenced the enclosing class's tparams, the instantiation substituted them away to `Unknown`, so the resulting callable lost the class's generic parameters. Detect that case in `bind_boundmethod`: when the bound object is a bare `ClassDef` and the method's tparams mention the class's tparams, skip instantiation so those tparams survive into the callable's signature. The bug-marked test now passes without expecting an `Unknown`.
fangyi-zhou
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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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@fangyi-zhou has imported this pull request. If you are a Meta employee, you can view this in D106576942. |
stroxler
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May 28, 2026
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@fangyi-zhou merged this pull request in b15abe7. |
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Summary
While investigating #2450 (#2450 (comment)), I noticed that generics handling via classmethod + paramspec is lossy -- the inferred type carries an
Unknowntype instead of a generic type. This diff attempts to fix the gap.sandbox
P.S. This was insufficient for the original constructor issue, as the code path was not shared after all. Nonetheless worth fixing
Test Plan
Regression test + test.py