Fix crash on lambda in generic context with generic method in body #15155
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@hauntsaninja FYI "Comment with mypy_primer diff" workflow failed with |
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Ugh, fixing #15156 |
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Diff from mypy_primer, showing the effect of this PR on open source code: graphql-core (https://github.com/graphql-python/graphql-core) got 1.05x slower (312.0s -> 329.1s)
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JukkaL
approved these changes
May 2, 2023
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Fixes #15060
The example in the issue contains another case where an erased type may legitimately appear in a generic function. Namely, when we have a lambda in a generic context, and its body contains a call to a generic method. First, since we infer the type of lambda in erased context, some of lambda parameters may get assigned a type containing erased components. Then, when accessing a generic method on such type we may get a callable that is both generic and has erased components, thus causing the crash (actually there are two very similar crashes depending on the details of the generic method).
Provided that we now have two legitimate cases for erased type appearing in
expand_type(), and special-casing (enabling) them would be tricky (a lot of functions will need to haveallow_erased_callables), I propose to simply remove the check.