[ty] Emit diagnostic for `NamedTuple` and `TypedDict` decorated with dataclass by charliermarsh · Pull Request #22672 · astral-sh/ruff

charliermarsh · 2026-01-18T01:17:41Z

Summary

Closes astral-sh/ty#2515.

Closes astral-sh/ty#2527.

astral-sh-bot · 2026-01-18T01:22:52Z

Typing conformance results

No changes detected ✅

astral-sh-bot · 2026-01-18T01:24:03Z

`mypy_primer` results

Changes were detected when running on open source projects

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 46 diagnostics
+ Found 47 diagnostics

static-frame (https://github.com/static-frame/static-frame)
- static_frame/core/index.py:580:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[TVContainer_co@loc, TVDtype@Index]`, found `InterGetItemLocReduces[Any | Bottom[Series[Any, Any]], TVDtype@Index]`
+ static_frame/core/index.py:580:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[TVContainer_co@loc, TVDtype@Index]`, found `InterGetItemLocReduces[Bottom[Series[Any, Any]] | Any, TVDtype@Index]`
- 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]`

No memory usage changes detected ✅

…lass`

AlexWaygood

Nice. I wonder if we should also flag enums and protocols decorated with @dataclass. Those also indicate that the user is probably very confused. And the enum docs explicitly lay out that adding @dataclass to an enum class is not supported

crates/ty_python_semantic/src/types/class.rs

crates/ty_python_semantic/resources/mdtest/named_tuple.md

crates/ty_python_semantic/resources/mdtest/typed_dict.md

crates/ty_python_semantic/src/types/infer/builder.rs

charliermarsh · 2026-01-18T13:27:23Z

crates/ty_python_semantic/resources/mdtest/named_tuple.md

+
+# TODO: This should emit `invalid-named-tuple` but currently emits `no-matching-overload`
+# due to overload resolution not matching `DynamicNamedTuple` against `type[_T]`.
+# error: [no-matching-overload]


This is turning out to be fairly annoying to fix.

Looks like it's a pre-existing issue, though? I think fine to defer it for this PR?

👍 Yeah that was my plan.

crates/ty_python_semantic/src/types/class.rs

crates/ty_python_semantic/src/types/call/bind.rs

crates/ty_python_semantic/src/types/diagnostic.rs

crates/ty_python_semantic/src/types/class.rs

crates/ty_python_semantic/src/types/call/bind.rs

AlexWaygood · 2026-01-18T14:50:58Z

crates/ty_python_semantic/src/types/diagnostic.rs

+    /// Applying `@dataclass` to a class that inherits from `NamedTuple`, `TypedDict`,
+    /// `Enum`, or `Protocol` is invalid:
+    ///
+    /// - `NamedTuple` and `TypedDict` classes will raise an exception at runtime when


Suggested change

/// - `NamedTuple` and `TypedDict` classes will raise an exception at runtime when

/// - `NamedTuple` and `TypedDict` classes will often raise an exception at runtime when

since you can avoid the TypedDict exception if you're very careful and use keyword arguments to instantiate the class:

>>> from typing import TypedDict >>> from dataclasses import dataclass >>> @dataclass ... class Foo(TypedDict): ... x: int ... >>> Foo(x=42) {'x': 42}

crates/ty_python_semantic/src/types/infer/builder.rs

AlexWaygood · 2026-01-18T14:52:11Z

crates/ty_python_semantic/src/types/infer/builder.rs

+                            class.name(self.db()),
+                        ));
+                        diagnostic.info(
+                            "An exception will be raised when instantiating the class at runtime",


Suggested change

"An exception will be raised when instantiating the class at runtime",

"An exception may be raised when instantiating the class at runtime",

crates/ty_python_semantic/src/types/infer/builder.rs

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

AlexWaygood · 2026-01-18T15:58:26Z

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

+
+### Protocol classes
+
+Applying `@dataclass` to a protocol class is invalid because protocols define interfaces and cannot


Suggested change

Applying `@dataclass` to a protocol class is invalid because protocols define interfaces and cannot

Applying `@dataclass` to a protocol class is invalid because protocols define abstract interfaces and cannot

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

AlexWaygood · 2026-01-18T16:01:09Z

crates/ty_python_semantic/resources/mdtest/named_tuple.md

+    y: str
+```
+
+The same error occurs with `dataclasses.dataclass` used as a function call:


Suggested change

The same error occurs with `dataclasses.dataclass` used as a function call:

The same error occurs with `dataclasses.dataclass` used with parentheses:

crates/ty_python_semantic/resources/mdtest/typed_dict.md

crates/ty_python_semantic/src/types/class.rs

AlexWaygood · 2026-01-18T16:11:53Z

crates/ty_python_semantic/src/types/infer/builder.rs

+                }
+                if class.is_typed_dict(self.db()) {


Suggested change

}

if class.is_typed_dict(self.db()) {

} else if class.is_typed_dict(self.db()) {

crates/ty_python_semantic/src/types/infer/builder.rs

## Summary Fixes some TODOs introduced in #22672 around cases like the following: ```python from collections import namedtuple from dataclasses import dataclass NT = namedtuple("NT", "x y") # error: [invalid-dataclass] "Cannot use `dataclass()` on a `NamedTuple` class" dataclass(NT) ``` On main, `dataclass(NT)` emits `# error: [no-matching-overload]` instead, which is wrong -- the overload does match! On main, the logic proceeds as follows: 1. `dataclass` has two overloads: - `dataclass(cls: type[_T], ...) -> type[_T]` - `dataclass(cls: None = None, ...) -> Callable[[type[_T]], type[_T]]` 2. When `dataclass(NT)` is called: - Arity check: Both overloads accept one positional argument, so both pass. - Type checking on first overload: `NT` matches `type[_T]`... but then `invalid_dataclass_target()` runs and adds `InvalidDataclassApplication` error - Type checking on second overload: `NT` doesn't match `None`, so we have a type error. 3. After type checking, both overloads have errors. 4. `matching_overload_index()` filters by `overload.as_result().is_ok()`, which checks if `errors.is_empty()`. Since both overloads have errors, neither matches... 5. We emit the "No overload matches arguments" error. Instead, we now differentiate between non-matching errors, and errors that occur when we _do_ match, but the call has some other semantic failure.

AlexWaygood added the ty Multi-file analysis & type inference label Jan 18, 2026

charliermarsh force-pushed the charlie/data-decorator branch from e3555d1 to e2b3a1c Compare January 18, 2026 01:21

[ty] Emit a diagnostic on NamedTuple classes decorated with `@datac…

47015ed

…lass`

charliermarsh force-pushed the charlie/data-decorator branch from e2b3a1c to 47015ed Compare January 18, 2026 01:28

charliermarsh marked this pull request as ready for review January 18, 2026 01:45

charliermarsh requested review from AlexWaygood, MichaReiser, carljm, dcreager and sharkdp as code owners January 18, 2026 01:45

AlexWaygood reviewed Jan 18, 2026

View reviewed changes

charliermarsh commented Jan 18, 2026

View reviewed changes

Review feedback

6e6e4af

charliermarsh force-pushed the charlie/data-decorator branch from 0615efb to d7ece7e Compare January 18, 2026 14:09

charliermarsh marked this pull request as draft January 18, 2026 14:09

AlexWaygood reviewed Jan 18, 2026

View reviewed changes

crates/ty_python_semantic/src/types/class.rs Outdated Show resolved Hide resolved

crates/ty_python_semantic/src/types/call/bind.rs Outdated Show resolved Hide resolved

crates/ty_python_semantic/src/types/diagnostic.rs Outdated Show resolved Hide resolved

charliermarsh added 2 commits January 18, 2026 09:20

Include enums and protocols

5dd23e4

Remove unused diagnostic

b450573

charliermarsh force-pushed the charlie/data-decorator branch from d7ece7e to b450573 Compare January 18, 2026 14:23

Apply simplification

eae09e2

charliermarsh marked this pull request as ready for review January 18, 2026 14:34

AlexWaygood reviewed Jan 18, 2026

View reviewed changes

Review feedback

3fd1211

charliermarsh force-pushed the charlie/data-decorator branch from a6579bc to 3fd1211 Compare January 18, 2026 15:31

AlexWaygood approved these changes Jan 18, 2026

View reviewed changes

Feedback

4fff0e7

charliermarsh enabled auto-merge (squash) January 18, 2026 17:14

charliermarsh merged commit 57c98a1 into main Jan 18, 2026
48 checks passed

charliermarsh deleted the charlie/data-decorator branch January 18, 2026 17:20

charliermarsh mentioned this pull request Jan 18, 2026

[ty] Avoid overload errors when detecting dataclass-on-tuple #22687

Merged

	/// - `NamedTuple` and `TypedDict` classes will raise an exception at runtime when
	/// - `NamedTuple` and `TypedDict` classes will often raise an exception at runtime when

	"An exception will be raised when instantiating the class at runtime",
	"An exception may be raised when instantiating the class at runtime",


		### Protocol classes

		Applying `@dataclass` to a protocol class is invalid because protocols define interfaces and cannot

	The same error occurs with `dataclasses.dataclass` used as a function call:
	The same error occurs with `dataclasses.dataclass` used with parentheses:

	}
	if class.is_typed_dict(self.db()) {
	} else if class.is_typed_dict(self.db()) {

Conversation

charliermarsh commented Jan 18, 2026

Summary

Uh oh!

astral-sh-bot bot commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

astral-sh-bot bot commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

mypy_primer results

Uh oh!

AlexWaygood left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

astral-sh-bot bot commented Jan 18, 2026 •

edited

Loading

astral-sh-bot bot commented Jan 18, 2026 •

edited

Loading

`mypy_primer` results