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Remove non-existing _DT from ordered dataclass #18846

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Remove non-existing _DT from ordered dataclass #18846

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65e950e
rm non-existing _DT from ordered dataclass
guitvcer Mar 27, 2025
bd56e27
Update test-data/unit/fixtures/tuple.pyi
hauntsaninja Mar 27, 2025
259e0e1
rm non-existing _DT from eq=True dataclass
guitvcer Mar 31, 2025
a5e4c77
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Mar 31, 2025
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6 changes: 1 addition & 5 deletions mypy/plugins/dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -291,11 +291,7 @@ def transform(self) -> bool:
self._api, self._cls, "__init__", args=args, return_type=NoneType()
)

if (
decorator_arguments["eq"]
and info.get("__eq__") is None
or decorator_arguments["order"]
):
if decorator_arguments["eq"] and info.get("__eq__") is None:
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Won't this still keep creating _DT on @dataclass(eq=True)? The problematic bit is actually creating a fake TypeVarExpr and putting it in dataclass' symbol table.

Furthermore, this will actually break @dataclass(eq=False, order=True) definitions, because below self._api.fail() does not abort early, we'll still create methods referencing non-existent _DT, maybe leading to some crashes down the road.

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Okay, I removed _DT from @dataclass(eq=True).

But I don't actually understand about @dataclass(eq=False, order=True) definitions, newbie in mypy:)

# Type variable for self types in generated methods.
obj_type = self._api.named_type("builtins.object")
self_tvar_expr = TypeVarExpr(
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12 changes: 12 additions & 0 deletions test-data/unit/check-dataclasses.test
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Expand Up @@ -2594,3 +2594,15 @@ class B2(B1): # E: A NamedTuple cannot be a dataclass
pass

[builtins fixtures/tuple.pyi]

[case testOrderedDataclassSelfTVARNotExist]
from dataclasses import dataclass

@dataclass(order=True)
class A:
b: int

a = A(1)
a._DT # E: "A" has no attribute "_DT"

[builtins fixtures/tuple.pyi]
1 change: 1 addition & 0 deletions test-data/unit/fixtures/tuple.pyi
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Expand Up @@ -9,6 +9,7 @@ _Tco = TypeVar('_Tco', covariant=True)
class object:
def __init__(self) -> None: pass
def __new__(cls) -> Self: ...
def __eq__(self, other) -> bool: pass

class type:
def __init__(self, *a: object) -> None: pass
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