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Avoid crash for starred match subject tuples #21499

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Avoid crash for starred match subject tuples #21499

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2 changes: 2 additions & 0 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6033,6 +6033,8 @@ def _get_recursive_sub_patterns_map(
typ_ = get_proper_type(typ)
if isinstance(expr, TupleExpr) and isinstance(typ_, TupleType):
# When matching a tuple expression with a sequence pattern, narrow individual tuple items
if any(isinstance(item, StarExpr) for item in expr.items):
return sub_patterns_map
assert len(expr.items) == len(typ_.items)
for item_expr, item_typ in zip(expr.items, typ_.items):
sub_patterns_map[item_expr] = item_typ
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10 changes: 10 additions & 0 deletions test-data/unit/check-python310.test
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Expand Up @@ -479,6 +479,16 @@ match m, (n, o), (p, (q, r)):
reveal_type(r) # N: Revealed type is "Literal[5]"
[builtins fixtures/tuple.pyi]

[case testMatchSequencePatternSubjectWithStarExprNoCrash]
# flags: --strict-equality --warn-unreachable
foo: int
bar: tuple[int, int]

match foo, *bar:
case _:
pass
[builtins fixtures/tuple.pyi]

[case testMatchSequencePatternSequencesLengthMismatchNoNarrowing]
# flags: --strict-equality --warn-unreachable
m: int
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