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Equality checks explode enums into unions of literals. Intersecting those unions used pairwise overlap tests, which is quadratic and made match statements after an == check very slow. Hash simple items instead and keep the overlap predicate only for the remaining cases. Fixes python#21997.
Narrowed singleton items are ProperType after get_proper_type, so annotate the list as list[Type] and read LiteralType.value from the proper item.
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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 #21997
After
if x == SomeEnum.MEMBER: return, mypy stores the rest of the enum as a literal union. A latermatch xthen did pairwiseis_overlapping_typeson those unions — O(N*M). On a 1200-member StrEnum that dominatedcProfile.I hash the simple items (
Literal/None/Never) and keep the overlap check only for the rest (needed for things likefloat | complexnarrowed byint).Tested with the new
MeetSuitecase pluscheck-python310.test/check-enum.test/check-narrowing.test.