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Fix single item enum match type exhaustion #16966

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merged 2 commits into from
Mar 7, 2024
Merged

Fix single item enum match type exhaustion #16966

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885a84e
Fix single item enum match type exhaustion
superosku Feb 29, 2024
45e1c2e
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hauntsaninja Mar 7, 2024
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2 changes: 1 addition & 1 deletion mypy/checkpattern.py
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Original file line number Diff line number Diff line change
Expand Up @@ -202,7 +202,7 @@ def visit_value_pattern(self, o: ValuePattern) -> PatternType:
typ = self.chk.expr_checker.accept(o.expr)
typ = coerce_to_literal(typ)
narrowed_type, rest_type = self.chk.conditional_types_with_intersection(
current_type, [get_type_range(typ)], o, default=current_type
current_type, [get_type_range(typ)], o, default=get_proper_type(typ)
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The issue was that on mypy/checker.py on conditional_types function, which is called by this self.chk.conditional_types_with_intersection , the conditional_types returns from here the default value:

mypy/mypy/checker.py

Line 7399 in 2037e4a

return default, UninhabitedType()

When on regular enum that has multiple choices the conditional_types returns here instead:

mypy/mypy/checker.py

Line 7415 in 2037e4a

return proposed_type, remaining_type

But the first one returns wrong default value, so I am changing the default value here to be what the get_proper_type returns instead.

)
if not isinstance(get_proper_type(narrowed_type), (LiteralType, UninhabitedType)):
return PatternType(narrowed_type, UnionType.make_union([narrowed_type, rest_type]), {})
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24 changes: 24 additions & 0 deletions test-data/unit/check-python310.test
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Original file line number Diff line number Diff line change
Expand Up @@ -1369,6 +1369,27 @@ match m3:
reveal_type(m3) # N: Revealed type is "Tuple[Union[builtins.int, builtins.str]]"
[builtins fixtures/tuple.pyi]

[case testMatchEnumSingleChoice]
from enum import Enum
from typing import NoReturn

def assert_never(x: NoReturn) -> None: ...

class Medal(Enum):
gold = 1

def f(m: Medal) -> None:
always_assigned: int | None = None
match m:
case Medal.gold:
always_assigned = 1
reveal_type(m) # N: Revealed type is "Literal[__main__.Medal.gold]"
case _:
assert_never(m)

reveal_type(always_assigned) # N: Revealed type is "builtins.int"
[builtins fixtures/bool.pyi]

[case testMatchLiteralPatternEnumNegativeNarrowing]
from enum import Enum
class Medal(Enum):
Expand All @@ -1388,10 +1409,13 @@ def f(m: Medal) -> int:
def g(m: Medal) -> int:
match m:
case Medal.gold:
reveal_type(m) # N: Revealed type is "Literal[__main__.Medal.gold]"
return 0
case Medal.silver:
reveal_type(m) # N: Revealed type is "Literal[__main__.Medal.silver]"
return 1
case Medal.bronze:
reveal_type(m) # N: Revealed type is "Literal[__main__.Medal.bronze]"
return 2

[case testMatchLiteralPatternEnumCustomEquals-skip]
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