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Fix OR pattern structural matching exhaustiveness #18119

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Merged
merged 2 commits into from
Nov 11, 2024
Merged

Fix OR pattern structural matching exhaustiveness #18119

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0857a9f
fix: modify `current_type` if not uninhabited
shenyih0ng Nov 7, 2024
ff90fbb
test: add unit test `testMatchOrPatternMatchExhaustivenes`
shenyih0ng Nov 10, 2024
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3 changes: 2 additions & 1 deletion mypy/checkpattern.py
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,8 @@ def visit_or_pattern(self, o: OrPattern) -> PatternType:
for pattern in o.patterns:
pattern_type = self.accept(pattern, current_type)
pattern_types.append(pattern_type)
current_type = pattern_type.rest_type
if not is_uninhabited(pattern_type.type):
current_type = pattern_type.rest_type

#
# Collect the final type
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16 changes: 16 additions & 0 deletions test-data/unit/check-python310.test
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Expand Up @@ -1702,6 +1702,22 @@ def f(x: int | str) -> int:
case str() as s:
return 1

[case testMatchOrPatternExhaustiveness]
from typing import NoReturn, Literal
def assert_never(x: NoReturn) -> None: ...

Color = Literal["blue", "green", "red"]
c: Color

match c:
case "blue":
reveal_type(c) # N: Revealed type is "Literal['blue']"
case "green" | "notColor":
reveal_type(c) # N: Revealed type is "Literal['green']"
case _:
assert_never(c) # E: Argument 1 to "assert_never" has incompatible type "Literal['red']"; expected "Never"
[typing fixtures/typing-typeddict.pyi]

[case testMatchAsPatternIntersection-skip]
class A: pass
class B: pass
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