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Fix narrowing of IntEnum and StrEnum types #17874

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Oct 4, 2024
Merged

Fix narrowing of IntEnum and StrEnum types #17874

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46 changes: 45 additions & 1 deletion mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5984,7 +5984,9 @@ def has_no_custom_eq_checks(t: Type) -> bool:
coerce_only_in_literal_context = True

expr_types = [operand_types[i] for i in expr_indices]
should_narrow_by_identity = all(map(has_no_custom_eq_checks, expr_types))
should_narrow_by_identity = all(
map(has_no_custom_eq_checks, expr_types)
) and not is_ambiguous_mix_of_enums(expr_types)

if_map: TypeMap = {}
else_map: TypeMap = {}
Expand Down Expand Up @@ -8604,3 +8606,45 @@ def visit_starred_pattern(self, p: StarredPattern) -> None:
self.lvalue = True
p.capture.accept(self)
self.lvalue = False


def is_ambiguous_mix_of_enums(types: list[Type]) -> bool:
"""Do types have IntEnum/StrEnum types that are potentially overlapping with other types?

If True, we shouldn't attempt type narrowing based on enum values, as it gets
too ambiguous.

For example, return True if there's an 'int' type together with an IntEnum literal.
However, IntEnum together with a literal of the same IntEnum type is not ambiguous.
"""
# We need these things for this to be ambiguous:
# (1) an IntEnum or StrEnum type
# (2) either a different IntEnum/StrEnum type or a non-enum type ("<other>")
#
# It would be slightly more correct to calculate this separately for IntEnum and
# StrEnum related types, as an IntEnum can't be confused with a StrEnum.
return len(_ambiguous_enum_variants(types)) > 1


def _ambiguous_enum_variants(types: list[Type]) -> set[str]:
result = set()
for t in types:
t = get_proper_type(t)
if isinstance(t, UnionType):
result.update(_ambiguous_enum_variants(t.items))
elif isinstance(t, Instance):
if t.last_known_value:
result.update(_ambiguous_enum_variants([t.last_known_value]))
elif t.type.is_enum and any(
base.fullname in ("enum.IntEnum", "enum.StrEnum") for base in t.type.mro
):
result.add(t.type.fullname)
elif not t.type.is_enum:
# These might compare equal to IntEnum/StrEnum types (e.g. Decimal), so
# let's be conservative
result.add("<other>")
elif isinstance(t, LiteralType):
result.update(_ambiguous_enum_variants([t.fallback]))
else:
result.add("<other>")
return result
8 changes: 0 additions & 8 deletions mypy/typeops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1078,14 +1078,6 @@ def custom_special_method(typ: Type, name: str, check_all: bool = False) -> bool
"""
typ = get_proper_type(typ)
if isinstance(typ, Instance):
if (
typ.type.is_enum
and name in ("__eq__", "__ne__")
and any(base.fullname in ("enum.IntEnum", "enum.StrEnum") for base in typ.type.mro)
):
# IntEnum and StrEnum values have non-straightfoward equality, so treat them
# as if they had custom __eq__ and __ne__
return True
method = typ.type.get(name)
if method and isinstance(method.node, (SYMBOL_FUNCBASE_TYPES, Decorator, Var)):
if method.node.info:
Expand Down
73 changes: 72 additions & 1 deletion test-data/unit/check-narrowing.test
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Original file line number Diff line number Diff line change
Expand Up @@ -2135,7 +2135,7 @@ else:
# mypy: strict-equality
from __future__ import annotations
from typing import Any
from enum import IntEnum, StrEnum
from enum import IntEnum

class IE(IntEnum):
X = 1
Expand Down Expand Up @@ -2178,6 +2178,71 @@ def f5(x: int) -> None:
reveal_type(x) # N: Revealed type is "builtins.int"
else:
reveal_type(x) # N: Revealed type is "Literal[__main__.IE.X]"

def f6(x: IE) -> None:
if x == IE.X:
reveal_type(x) # N: Revealed type is "Literal[__main__.IE.X]"
else:
reveal_type(x) # N: Revealed type is "Literal[__main__.IE.Y]"
[builtins fixtures/primitives.pyi]

[case testNarrowingWithIntEnum2]
# mypy: strict-equality
from __future__ import annotations
from typing import Any
from enum import IntEnum, Enum

class MyDecimal: ...

class IE(IntEnum):
X = 1
Y = 2

class IE2(IntEnum):
X = 1
Y = 2

class E(Enum):
X = 1
Y = 2

def f1(x: IE | MyDecimal) -> None:
if x == IE.X:
reveal_type(x) # N: Revealed type is "Union[__main__.IE, __main__.MyDecimal]"
else:
reveal_type(x) # N: Revealed type is "Union[__main__.IE, __main__.MyDecimal]"

def f2(x: E | bytes) -> None:
if x == E.X:
reveal_type(x) # N: Revealed type is "Literal[__main__.E.X]"
else:
reveal_type(x) # N: Revealed type is "Union[Literal[__main__.E.Y], builtins.bytes]"

def f3(x: IE | IE2) -> None:
if x == IE.X:
reveal_type(x) # N: Revealed type is "Union[__main__.IE, __main__.IE2]"
else:
reveal_type(x) # N: Revealed type is "Union[__main__.IE, __main__.IE2]"

def f4(x: IE | E) -> None:
if x == IE.X:
reveal_type(x) # N: Revealed type is "Literal[__main__.IE.X]"
elif x == E.X:
reveal_type(x) # N: Revealed type is "Literal[__main__.E.X]"
else:
reveal_type(x) # N: Revealed type is "Union[Literal[__main__.IE.Y], Literal[__main__.E.Y]]"

def f5(x: E | str | int) -> None:
if x == E.X:
reveal_type(x) # N: Revealed type is "Literal[__main__.E.X]"
else:
reveal_type(x) # N: Revealed type is "Union[Literal[__main__.E.Y], builtins.str, builtins.int]"

def f6(x: IE | Any) -> None:
if x == IE.X:
reveal_type(x) # N: Revealed type is "Union[__main__.IE, Any]"
else:
reveal_type(x) # N: Revealed type is "Union[__main__.IE, Any]"
[builtins fixtures/primitives.pyi]

[case testNarrowingWithStrEnum]
Expand Down Expand Up @@ -2205,4 +2270,10 @@ def f3(x: object) -> None:
reveal_type(x) # N: Revealed type is "builtins.object"
else:
reveal_type(x) # N: Revealed type is "builtins.object"

def f4(x: SE) -> None:
if x == SE.A:
reveal_type(x) # N: Revealed type is "Literal[__main__.SE.A]"
else:
reveal_type(x) # N: Revealed type is "Literal[__main__.SE.B]"
[builtins fixtures/primitives.pyi]
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