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Expanding *Ts with a union replacement (e.g. tuple[*tuple[Any, ...]] | Any inferred from a conditional expression used as a type argument) raised RuntimeError from expand_unpack, since unions were not handled there. Carry the union over into the expansion instead, same as the existing Any/Never fallback above. (GH#22108)
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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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Fixes #22108
expand_unpackraisedRuntimeError: Invalid type replacement to expand: tuple[*tuple[Any, ...]] | Anywhen a type variable tuple was expanded with a union replacement. Unions reach this point when a conditional expression is used as a type argument:infer_function_type_arguments_using_contextinfers the union as the type argument, andapply_generic_argumentsthen expands it (see the traceback in the issue).Change
Add
UnionTypeto the carry-over fallback inexpand_unpack, same as the existingAnyType/UninhabitedTypebranch directly above it (whose comment already describes this exact pattern: "These types may appear here as a result of user error or failed inference"). The union is carried over into*tuple[<union>]instead of crashing, preserving the type information.Tests
test_expand_unpack_union_replacementinmypy/test/testtypes.pyconstructstuple[*Ts]with the isomorphic union replacement from the issue and asserts the expansion completes with the union carried over. It fails with the RuntimeError on unpatched code and passes with the fix. The existing expand tests (test_expand_*) and the variadic checker tests (typevar_tuple/variadicselections, 168 cases) pass unchanged.