dataclasses_hash.py

"""
Tests the synthesis of the __hash__ method in a dataclass.
"""

from dataclasses import dataclass
from typing import Hashable, assert_type


@dataclass
class DC1:
    a: int


assert_type(DC1.__hash__, None)

# These should generate errors because DC1 isn't hashable.
DC1(0).__hash__()  # E
v1: Hashable = DC1(0)  # E


@dataclass(eq=True, frozen=True)
class DC2:
    a: int


# Because `DC2` is frozen, type checkers should synthesize
# a callable `__hash__` method for it, and therefore should
# emit a diagnostic here:
assert_type(DC2.__hash__, None)  # E

DC2(0).__hash__()  # OK
v2: Hashable = DC2(0)  # OK


@dataclass(eq=True)
class DC3:
    a: int


assert_type(DC3.__hash__, None)

# These should generate errors because DC3 isn't hashable.
DC3(0).__hash__()  # E
v3: Hashable = DC3(0)  # E


@dataclass(frozen=True)
class DC4:
    a: int


# Because `DC4` is frozen, type checkers should synthesize
# a callable `__hash__` method for it, and therefore should
# emit a diagnostic here:
assert_type(DC4.__hash__, None)  # E

DC4(0).__hash__()  # OK
v4: Hashable = DC4(0)  # OK


@dataclass(eq=True, unsafe_hash=True)
class DC5:
    a: int


# Type checkers should synthesize a callable `__hash__`
# method for `DC5` due to `unsafe_hash=True`, and therefore
# should emit a diagnostic here:
assert_type(DC5.__hash__, None)  # E

DC5(0).__hash__()  # OK
v5: Hashable = DC5(0)  # OK


@dataclass(eq=True)
class DC6:
    a: int

    def __hash__(self) -> int:
        return 0


# Type checkers should respect the manually defined `__hash__`
# method for `DC6`, and therefore should emit a diagnostic here:
assert_type(DC6.__hash__, None)  # E

DC6(0).__hash__()  # OK
v6: Hashable = DC6(0)  # OK


@dataclass(frozen=True)
class DC7:
    a: int

    def __eq__(self, other) -> bool:
        return self.a == other.a


# Because `DC7` is frozen, type checkers should synthesize
# a callable `__hash__` method for it, and therefore should
# emit a diagnostic here:
assert_type(DC7.__hash__, None)  # E

DC7(0).__hash__()  # OK
v7: Hashable = DC7(0)  # OK