[ty] diagnostic on overridden `__setattr__` and `__delattr__` in frozen dataclasses by thejchap · Pull Request #21430 · astral-sh/ruff

thejchap · 2025-11-13T14:48:35Z

Summary

this pr adds an invalid-dataclass-override diagnostic when a custom __setattr__ or __delattr__ is defined on a dataclass where frozen=True (docs)

Runtime exception

Traceback (most recent call last):
  File "/Users/justinchapman/src/ty-playground/main.py", line 4, in <module>
    @dataclass(frozen=True)
     ~~~~~~~~~^^^^^^^^^^^^^
  File "/Users/justinchapman/.local/share/uv/python/cpython-3.13.0-macos-aarch64-none/lib/python3.13/dataclasses.py", line 1295, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
                          frozen, match_args, kw_only, slots,
                          weakref_slot)
  File "/Users/justinchapman/.local/share/uv/python/cpython-3.13.0-macos-aarch64-none/lib/python3.13/dataclasses.py", line 1157, in _process_class
    func_builder.add_fns_to_class(cls)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "/Users/justinchapman/.local/share/uv/python/cpython-3.13.0-macos-aarch64-none/lib/python3.13/dataclasses.py", line 516, in add_fns_to_class
    raise TypeError(error_msg)
TypeError: Cannot overwrite attribute __setattr__ in class A

Diagnostic

error[invalid-dataclass-override]: Cannot overwrite attribute __setattr__ in class A
 --> /Users/justinchapman/src/ty-playground/main.py:6:5
  |
4 | @dataclass(frozen=True)
5 | class A:
6 |     def __setattr__(self, name: str, value: object) -> None: ...
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
info: __setattr__
info: rule `invalid-dataclass-override` is enabled by default

Found 1 diagnostic

Test Plan

new mdtests
e2e
the attrs mypy primer diff looks to be a true positive - the other results have been unpredictable and have changed every time i pushed new code, even if the diagnostic logic didn't change...

crates/ty_python_semantic/resources/mdtest/dataclasses/dataclasses.md

astral-sh-bot · 2025-11-13T14:50:42Z

Typing conformance results

No changes detected ✅

astral-sh-bot · 2025-11-13T14:51:53Z

`mypy_primer` results

Changes were detected when running on open source projects

attrs (https://github.com/python-attrs/attrs)
+ tests/test_setattr.py:374:17: error[invalid-dataclass-override] Cannot overwrite attribute `__setattr__` in class `CustomSetAttr`
- Found 627 diagnostics
+ Found 628 diagnostics

prefect (https://github.com/PrefectHQ/prefect)
- src/integrations/prefect-dbt/prefect_dbt/core/settings.py:94:28: error[invalid-assignment] Object of type `T@resolve_block_document_references | dict[str, Any] | str | ... omitted 4 union elements` is not assignable to `dict[str, Any]`
+ src/integrations/prefect-dbt/prefect_dbt/core/settings.py:94:28: error[invalid-assignment] Object of type `T@resolve_block_document_references | dict[str, Any]` is not assignable to `dict[str, Any]`
- src/integrations/prefect-dbt/prefect_dbt/core/settings.py:99:28: error[invalid-assignment] Object of type `T@resolve_variables | str | int | ... omitted 4 union elements` is not assignable to `dict[str, Any]`
+ src/integrations/prefect-dbt/prefect_dbt/core/settings.py:99:28: error[invalid-assignment] Object of type `T@resolve_variables | dict[str, Any]` is not assignable to `dict[str, Any]`
- src/prefect/cli/deploy/_core.py:86:21: error[invalid-assignment] Object of type `T@resolve_block_document_references | dict[str, Any] | str | ... omitted 4 union elements` is not assignable to `dict[str, Any]`
+ src/prefect/cli/deploy/_core.py:86:21: error[invalid-assignment] Object of type `T@resolve_block_document_references | dict[str, Any]` is not assignable to `dict[str, Any]`
- src/prefect/cli/deploy/_core.py:87:21: error[invalid-assignment] Object of type `T@resolve_variables | str | int | ... omitted 4 union elements` is not assignable to `dict[str, Any]`
+ src/prefect/cli/deploy/_core.py:87:21: error[invalid-assignment] Object of type `T@resolve_variables` is not assignable to `dict[str, Any]`
- src/prefect/deployments/runner.py:795:70: warning[possibly-missing-attribute] Attribute `__name__` may be missing on object of type `Unknown | ((...) -> Any)`
+ src/prefect/deployments/runner.py:795:70: warning[possibly-missing-attribute] Attribute `__name__` may be missing on object of type `Unknown | (((...) -> Any) & ((*args: object, **kwargs: object) -> object))`
- src/prefect/deployments/steps/core.py:137:38: error[invalid-argument-type] Argument is incorrect: Expected `T@resolve_variables`, found `T@resolve_block_document_references | dict[str, Any] | str | ... omitted 4 union elements`
+ src/prefect/deployments/steps/core.py:137:38: error[invalid-argument-type] Argument is incorrect: Expected `T@resolve_variables`, found `T@resolve_block_document_references | dict[str, Any]`
- src/prefect/flow_engine.py:812:32: error[invalid-await] `Unknown | R@FlowRunEngine | Coroutine[Any, Any, R@FlowRunEngine]` is not awaitable
- src/prefect/flow_engine.py:1401:24: error[invalid-await] `Unknown | R@AsyncFlowRunEngine | Coroutine[Any, Any, R@AsyncFlowRunEngine]` is not awaitable
- src/prefect/flow_engine.py:1482:43: error[invalid-argument-type] Argument to function `next` is incorrect: Expected `SupportsNext[Unknown]`, found `Unknown | R@run_generator_flow_sync`
- src/prefect/flow_engine.py:1490:21: warning[possibly-missing-attribute] Attribute `throw` may be missing on object of type `Unknown | R@run_generator_flow_sync`
- src/prefect/flow_engine.py:1524:44: warning[possibly-missing-attribute] Attribute `__anext__` may be missing on object of type `Unknown | R@run_generator_flow_async`
- src/prefect/flow_engine.py:1531:25: warning[possibly-missing-attribute] Attribute `throw` may be missing on object of type `Unknown | R@run_generator_flow_async`
- src/prefect/flows.py:286:34: error[unresolved-attribute] Object of type `(**P@Flow) -> R@Flow` has no attribute `__name__`
+ src/prefect/flows.py:286:34: error[unresolved-attribute] Object of type `((**P@Flow) -> R@Flow) & ((*args: object, **kwargs: object) -> object)` has no attribute `__name__`
- src/prefect/flows.py:404:68: error[unresolved-attribute] Object of type `(**P@Flow) -> R@Flow` has no attribute `__name__`
+ src/prefect/flows.py:404:68: error[unresolved-attribute] Object of type `((**P@Flow) -> R@Flow) & ((*args: object, **kwargs: object) -> object)` has no attribute `__name__`
+ src/prefect/flows.py:1750:53: warning[unused-ignore-comment] Unused blanket `type: ignore` directive
- src/prefect/utilities/templating.py:320:13: error[invalid-assignment] Invalid subscript assignment with key of type `object` and value of type `T@resolve_block_document_references | dict[str, Any] | str | ... omitted 4 union elements` on object of type `dict[str, Any]`
+ src/prefect/utilities/templating.py:320:13: error[invalid-assignment] Invalid subscript assignment with key of type `object` and value of type `T@resolve_block_document_references | dict[str, Any]` on object of type `dict[str, Any]`
- src/prefect/utilities/templating.py:323:16: error[invalid-return-type] Return type does not match returned value: expected `T@resolve_block_document_references | dict[str, Any]`, found `list[T@resolve_block_document_references | dict[str, Any] | str | ... omitted 5 union elements]`
+ src/prefect/utilities/templating.py:323:16: error[invalid-return-type] Return type does not match returned value: expected `T@resolve_block_document_references | dict[str, Any]`, found `list[T@resolve_block_document_references | dict[str, Any] | Unknown]`
- src/prefect/utilities/templating.py:437:16: error[invalid-return-type] Return type does not match returned value: expected `T@resolve_variables`, found `dict[object, T@resolve_variables | str | int | ... omitted 5 union elements]`
+ src/prefect/utilities/templating.py:437:16: error[invalid-return-type] Return type does not match returned value: expected `T@resolve_variables`, found `dict[object, T@resolve_variables | Unknown]`
- src/prefect/utilities/templating.py:442:16: error[invalid-return-type] Return type does not match returned value: expected `T@resolve_variables`, found `list[T@resolve_variables | str | int | ... omitted 5 union elements]`
+ src/prefect/utilities/templating.py:442:16: error[invalid-return-type] Return type does not match returned value: expected `T@resolve_variables`, found `list[T@resolve_variables | Unknown]`
- src/prefect/workers/base.py:232:13: error[invalid-argument-type] Argument is incorrect: Expected `T@resolve_variables`, found `T@resolve_block_document_references | dict[str, Any] | str | ... omitted 4 union elements`
+ src/prefect/workers/base.py:232:13: error[invalid-argument-type] Argument is incorrect: Expected `T@resolve_variables`, found `T@resolve_block_document_references | dict[str, Any]`
- src/prefect/workers/base.py:234:20: error[invalid-argument-type] Argument expression after ** must be a mapping type: Found `T@resolve_variables | str | int | ... omitted 4 union elements`
+ src/prefect/workers/base.py:234:20: error[invalid-argument-type] Argument expression after ** must be a mapping type: Found `T@resolve_variables`
- Found 5411 diagnostics
+ Found 5406 diagnostics

scikit-build-core (https://github.com/scikit-build/scikit-build-core)
- src/scikit_build_core/build/wheel.py:99:20: error[no-matching-overload] No overload of bound method `__init__` matches arguments
- Found 47 diagnostics
+ Found 46 diagnostics

static-frame (https://github.com/static-frame/static-frame)
- static_frame/core/bus.py:671:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[Bus[Any], object_]`, found `InterGetItemLocReduces[Bus[Any] | Bottom[Series[Any, Any]] | ndarray[Never, Never] | ... omitted 6 union elements, object_]`
+ static_frame/core/bus.py:671:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[Bus[Any], object_]`, found `InterGetItemLocReduces[Bus[Any] | Bottom[Index[Any]] | TypeBlocks | ... omitted 6 union elements, object_]`
- static_frame/core/node_selector.py:526:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[TVContainer_co@InterfaceSelectQuartet, Any]`, found `InterGetItemLocReduces[Bottom[Series[Any, Any]] | Unknown, Any]`
+ static_frame/core/node_selector.py:526:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[TVContainer_co@InterfaceSelectQuartet, Any]`, found `InterGetItemLocReduces[Unknown | Bottom[Series[Any, Any]], Any]`
- static_frame/core/series.py:772:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Series[Any, Any], TVDtype@Series]`, found `InterGetItemILocReduces[Series[Any, Any] | Bottom[Index[Any]] | TypeBlocks | ... omitted 6 union elements, TVDtype@Series]`
+ static_frame/core/series.py:772:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Series[Any, Any], TVDtype@Series]`, found `InterGetItemILocReduces[Series[Any, Any] | ndarray[Never, Never] | TypeBlocks | ... omitted 6 union elements, TVDtype@Series]`
- static_frame/core/yarn.py:418:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Yarn[Any], object_]`, found `InterGetItemILocReduces[Yarn[Any] | Bottom[Index[Any]] | TypeBlocks | ... omitted 6 union elements, object_]`
+ static_frame/core/yarn.py:418:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Yarn[Any], object_]`, found `InterGetItemILocReduces[Yarn[Any] | ndarray[Never, Never] | TypeBlocks | ... omitted 6 union elements, object_]`

rotki (https://github.com/rotki/rotki)
- rotkehlchen/chain/decoding/tools.py:96:44: warning[unused-ignore-comment] Unused blanket `type: ignore` directive
- rotkehlchen/chain/decoding/tools.py:99:13: error[invalid-argument-type] Argument to function `decode_transfer_direction` is incorrect: Expected `Sequence[A@BaseDecoderTools]`, found `Unknown | tuple[BTCAddress, ...] | tuple[ChecksumAddress, ...] | tuple[SubstrateAddress, ...] | tuple[SolanaAddress, ...]`
- rotkehlchen/chain/decoding/tools.py:100:62: warning[unused-ignore-comment] Unused blanket `type: ignore` directive
+ rotkehlchen/chain/decoding/tools.py:97:13: error[invalid-argument-type] Argument to function `decode_transfer_direction` is incorrect: Expected `BTCAddress | ChecksumAddress | SubstrateAddress | SolanaAddress`, found `A@BaseDecoderTools`
+ rotkehlchen/chain/decoding/tools.py:98:13: error[invalid-argument-type] Argument to function `decode_transfer_direction` is incorrect: Expected `BTCAddress | ChecksumAddress | SubstrateAddress | SolanaAddress | None`, found `A@BaseDecoderTools | None`
- Found 2057 diagnostics
+ Found 2056 diagnostics

core (https://github.com/home-assistant/core)
- homeassistant/util/variance.py:47:12: error[invalid-return-type] Return type does not match returned value: expected `(**_P@ignore_variance) -> _R@ignore_variance`, found `_Wrapped[_P@ignore_variance, _R@ignore_variance | int | float | datetime, _P@ignore_variance, _R@ignore_variance | int | float | datetime]`
- Found 14492 diagnostics
+ Found 14491 diagnostics

No memory usage changes detected ✅

sharkdp · 2025-12-09T08:30:25Z

Thank you for your contribution. I did not have time to review this in detail yet. One question upfront: would it be reasonable to use the existing invalid-override diagnostic here instead?

thejchap · 2025-12-09T14:55:32Z

@sharkdp i am not sure - one thing that seems like it could be nice over time is to have better diagnostic info for this specific case (for example highlighting the frozen argument similar to the runtime error) which wouldn't be applicable to the more generic LSP violation that invalid-method-override is referring to

i will defer to you though - does seem reasonable!

AlexWaygood · 2025-12-09T15:16:55Z

I think it's better to have a different error code here. invalid-method-override is specifically about Liskov violations, which this isn't. I've been wondering about renaming it to unsound-method-override, since there are obviously lots of other ways in which method overrides can be invalid.

AlexWaygood · 2025-12-09T15:19:15Z

I think it would be good to give the error code a name that makes it clear it's specifically about dataclasses, though, which the documentation of the rule makes clear

carljm · 2025-12-09T22:12:51Z

We may add similar rules in future for things you're not allowed to override on a tuple subclass. Would we want those to use the same rule as the dataclass case, or a distinct rule for tuples? That may influence how we name this rule.

carljm · 2025-12-09T22:13:48Z

(Having said that, I think maybe a different rule, since the tuple case won't be things that raise at runtime, just things that could cause unsoundness. So it would be reasonable to want to disable the one rule but not the other; and they should maybe have different severities. So I think I'd support naming this rule in a dataclass-specific way.)

thejchap · 2025-12-11T03:23:47Z

@AlexWaygood took another stab at naming based on how i interpreted your and Carl's comments

cc @carljm - i wasn't sure the best way to pull these comments over from #21820. i did refactor has_dataclass_param to be a method on ClassLiteral instead of a closure in own_synthesized_member, but i didn't change any of the actual logic - if you want to elaborate a bit more on the refactor you had in mind i can either try to implement it here, or just add a comment

AlexWaygood · 2025-12-18T16:28:57Z

Thank you! Sorry for the back-and-forth on naming... maybe invalid-dataclass-override might be good?

The name clearly indicates that it's dataclass-related
But it's a bit shorter than unsound-dataclass-method-override
And I'm not sure "unsound" is the best adjective to use here, because to me it implies that this is detecting sort-of an abstract theoretical issue rather than something that would raise TypeError at runtime. That's why I want to rename Liskov violations to unsound-method-override -- because the error code that detects Liskov violations is kinda abstract and theoretical. But this error code is different to the Liskov error code -- it's not really abstract and theoretical, it's detecting something that's going to cause TypeError to always be raised at runtime. So the stronger adjective invalid seems more fitting here.

thejchap · 2025-12-22T06:37:29Z

@AlexWaygood ah! thanks for clarifying. sounds good - done

carljm · 2025-12-24T02:00:28Z

@thejchap sorry for the slow response time! We've been getting swamped since the beta and this got lost in my notifications. I would say don't worry about those comments for this PR, let's just get the functionality right, better to separate things when separable. Those comments are mostly about making sure we handle various kinds of dataclass-transforms correctly, and that's kind of orthogonal to this PR anyway.

thejchap · 2025-12-24T23:32:53Z

Sounds good - I think this is ready for re-review then - let me know if I'm missing anything!

MichaReiser · 2025-12-29T09:49:34Z

Thank you for your work on feature. Almost the entire team is out this week. It may take a few days before someone finds time to review your PR. Happy holidays.

thejchap · 2025-12-29T19:30:01Z

@MichaReiser thanks! Happy holidays

thejchap · 2026-01-15T01:12:12Z

@AlexWaygood @MichaReiser hi! Just wanted to check on this one - I had been interested in continuing down this road on the diagnostics for overridden comparison dunder methods on order=True dataclasses as well so was curious on any feedback on the direction in this PR

AlexWaygood · 2026-01-15T12:28:14Z

Sorry, we still have a bit of a PR backlog from the Christmas holidays :-(

I haven't forgotten about this PR and I promise we will get to it. I've been trying to munch through review of as many PRs as possible this week.

thejchap · 2026-01-16T22:19:43Z

Ah no worries! Thanks for the update

…ataclasses astral-sh/ty#111

https://github.com/astral-sh/ruff/pull/21430\#issuecomment-3671108403

carljm

Looks great! Sorry again for the really slow review, we definitely aim to do better than this. This PR just hit the exact wrong time frame with beta release and then holidays :)

thejchap commented Nov 13, 2025

View reviewed changes

crates/ty_python_semantic/resources/mdtest/dataclasses/dataclasses.md Outdated Show resolved Hide resolved

thejchap force-pushed the thejchap/frozen-setattr branch from dad0985 to 5c3f14a Compare November 15, 2025 05:58

thejchap force-pushed the thejchap/frozen-setattr branch from 5c3f14a to 3272ab1 Compare November 30, 2025 02:24

thejchap force-pushed the thejchap/frozen-setattr branch 10 times, most recently from b7e81c1 to bcf0226 Compare December 8, 2025 00:35

thejchap marked this pull request as ready for review December 8, 2025 00:39

thejchap requested review from AlexWaygood, MichaReiser, carljm, dcreager and sharkdp as code owners December 8, 2025 00:39

AlexWaygood added the ty Multi-file analysis & type inference label Dec 8, 2025

thejchap force-pushed the thejchap/frozen-setattr branch from bcf0226 to d76d6ca Compare December 11, 2025 02:44

thejchap marked this pull request as draft December 11, 2025 02:44

thejchap force-pushed the thejchap/frozen-setattr branch 4 times, most recently from a576b6e to 7611878 Compare December 11, 2025 03:23

thejchap marked this pull request as ready for review December 11, 2025 03:23

AlexWaygood mentioned this pull request Dec 13, 2025

Advanced dataclass support astral-sh/ty#111

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19 tasks

thejchap force-pushed the thejchap/frozen-setattr branch from 7611878 to a1cdc0c Compare December 18, 2025 11:05

thejchap force-pushed the thejchap/frozen-setattr branch from a1cdc0c to c6148aa Compare December 22, 2025 06:26

thejchap mentioned this pull request Dec 23, 2025

[ty] diagnostic on overridden comparison dunder methods on order=True dataclasses thejchap/ruff#3

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thejchap force-pushed the thejchap/frozen-setattr branch 2 times, most recently from 6064263 to 6036d5a Compare January 7, 2026 02:38

thejchap added 2 commits January 16, 2026 18:04

[ty] diagnostic on overridden __setattr__ and __delattr__ in frozen d…

449893c

…ataclasses astral-sh/ty#111

[ty] rename diagnostic for overriding dataclass methods

9e23d3d

https://github.com/astral-sh/ruff/pull/21430\#issuecomment-3671108403

carljm force-pushed the thejchap/frozen-setattr branch from 6036d5a to 9e23d3d Compare January 17, 2026 02:07

re-use field_policy

d4de879

carljm approved these changes Jan 17, 2026

View reviewed changes

carljm enabled auto-merge (squash) January 17, 2026 02:23

carljm merged commit 938c1c5 into astral-sh:main Jan 17, 2026
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thejchap commented Nov 13, 2025 • edited by carljm Loading Uh oh! There was an error while loading. Please reload this page.

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thejchap commented Nov 13, 2025 •

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`mypy_primer` results