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[ty] Infer single-valuedness for enums based on int/str (#19510)

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## Summary

We previously didn't recognize `Literal[Color.RED]` as single-valued, if
the enum also derived from `str` or `int`:
```py
from enum import Enum

class Color(str, Enum):
    RED = "red"
    GREEN = "green"
    BLUE = "blue"

def _(color: Color):
    if color == Color.RED:
        reveal_type(color)  # previously: Color, now: Literal[Color.RED]
```

The reason for that was that `int` and `str` have "custom" `__eq__` and
`__ne__` implementations that return `bool`. We do not treat enum
literals from classes with custom `__eq__` and `__ne__` implementations
as single-valued, but of course we know that `int.__eq__` and
`str.__eq__` are well-behaved.

## Test Plan

New Markdown tests.
This commit is contained in:
David Peter 2025-07-23 15:55:42 +02:00 • committed by GitHub
parent cc5885e564
commit 5a55bab3f3
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3 changed files with 39 additions and 3 deletions
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16
crates/ty_python_semantic/resources/mdtest/type_properties/is_single_valued.md
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@ -71,6 +71,14 @@ class CustomNeEnum(Enum):
def __ne__(self, other: object) -> bool:
return False
class StrEnum(str, Enum):
A = "a"
B = "b"
class IntEnum(int, Enum):
A = 1
B = 2
static_assert(is_single_valued(Literal[NormalEnum.NO]))
static_assert(is_single_valued(Literal[NormalEnum.YES]))
static_assert(not is_single_valued(NormalEnum))
@ -89,4 +97,12 @@ static_assert(not is_single_valued(CustomEqEnum))
static_assert(not is_single_valued(Literal[CustomNeEnum.NO]))
static_assert(not is_single_valued(Literal[CustomNeEnum.YES]))
static_assert(not is_single_valued(CustomNeEnum))
static_assert(is_single_valued(Literal[StrEnum.A]))
static_assert(is_single_valued(Literal[StrEnum.B]))
static_assert(not is_single_valued(StrEnum))
static_assert(is_single_valued(Literal[IntEnum.A]))
static_assert(is_single_valued(Literal[IntEnum.B]))
static_assert(not is_single_valued(IntEnum))
```