[ty] Correct return type for synthesized NamedTuple.__new__ methods by bxff · Pull Request #22625 · astral-sh/ruff

bxff · 2026-01-16T17:58:13Z

Summary

Fixed the synthesized NamedTuple.__new__ method to correctly return Self instead of the base class literal. This resolves invalid-return-type errors in subclasses that override __new__ and call super().__new__().

The change introduces a synthetic Self type variable for the __new__ signature, making it properly generic. The cls parameter now uses type[Self] and the return type is Self, matching Python's runtime behavior and typing conventions.

Fixes astral-sh/ty#2522

Test Plan

Added regression test to crates/ty_python_semantic/resources/mdtest/named_tuple.md verifying:
- reveal_type(instance) inside Child.__new__ shows Self@__new__
- reveal_type(Child(1, 2)) correctly shows Child

Updated existing assertions in named_tuple.md to reflect the new generic signature:

reveal_type(Url.__new__)  # revealed: [Self](cls: type[Self], protocol: str, host: str, port: int | None = ...) -> Self

- Uses a synthetic `Self` type variable for `__new__` in [NamedTuple](cci:2://file:///Users/dexdevlon/Developer/Github/ruff/crates/ty_python_semantic/src/types/class.rs:5307:0-5333:1) synthesis. - Types the `cls` parameter as `type[Self]` and sets the return type to `Self`. - This ensures that `super().__new__` calls in subclasses correctly resolve to the subclass type, fixing astral-sh/ty#2522. - Updated [named_tuple.md](cci:7://file:///Users/dexdevlon/Developer/Github/ruff/crates/ty_python_semantic/resources/mdtest/named_tuple.md:0:0-0:0) assertions to match the new generic display and added a dedicated regression test case.

astral-sh-bot · 2026-01-16T18:00:45Z

Typing conformance results

No changes detected ✅

astral-sh-bot · 2026-01-16T18:01:22Z

`mypy_primer` results

Changes were detected when running on open source projects

paasta (https://github.com/yelp/paasta)
- paasta_tools/iptables.py:38:9: error[unresolved-attribute] Object of type `_RuleBase` has no attribute `validate`
- Found 1104 diagnostics
+ Found 1103 diagnostics

pydantic (https://github.com/pydantic/pydantic)
- pydantic/fields.py:943:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:943:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:983:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:983:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1026:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1026:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1066:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1066:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1109:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1109:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1148:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1148:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1188:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1188:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1567:13: error[invalid-argument-type] Argument is incorrect: Expected `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`, found `Top[dict[Unknown, Unknown]] | (((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) & ~Top[dict[Unknown, Unknown]]) | None`
+ pydantic/fields.py:1567:13: error[invalid-argument-type] Argument is incorrect: Expected `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`, found `Top[dict[Unknown, Unknown]] | (((dict[str, Divergent], /) -> None) & ~Top[dict[Unknown, Unknown]]) | None`

mongo-python-driver (https://github.com/mongodb/mongo-python-driver)
- pymongo/driver_info.py:45:16: error[invalid-return-type] Return type does not match returned value: expected `pymongo.driver_info.DriverInfo @ pymongo/driver_info.py:25:7`, found `pymongo.driver_info.DriverInfo @ pymongo/driver_info.py:25:18`
- Found 441 diagnostics
+ Found 440 diagnostics

cloud-init (https://github.com/canonical/cloud-init)
- cloudinit/lifecycle.py:52:16: error[invalid-return-type] Return type does not match returned value: expected `cloudinit.lifecycle.Version @ cloudinit/lifecycle.py:19:7`, found `cloudinit.lifecycle.Version @ cloudinit/lifecycle.py:20:5`
- Found 1170 diagnostics
+ Found 1169 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]` 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] | str | ... 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/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/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: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:87:21: error[invalid-assignment] Object of type `T@resolve_variables` 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/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/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/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: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: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: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: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: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: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/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/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: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:234:20: error[invalid-argument-type] Argument expression after ** must be a mapping type: Found `T@resolve_variables`
+ 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`

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

aiohttp (https://github.com/aio-libs/aiohttp)
- aiohttp/helpers.py:136:16: error[invalid-return-type] Return type does not match returned value: expected `aiohttp.helpers.BasicAuth @ aiohttp/helpers.py:121:7`, found `aiohttp.helpers.BasicAuth @ aiohttp/helpers.py:121:17`
- Found 181 diagnostics
+ Found 180 diagnostics

django-stubs (https://github.com/typeddjango/django-stubs)
+ mypy_django_plugin/lib/helpers.py:226:20: error[invalid-argument-type] Argument is incorrect: Argument type `Model` does not satisfy upper bound `DjangoModel` of type variable `Self`
+ mypy_django_plugin/lib/helpers.py:226:20: error[invalid-argument-type] Argument is incorrect: Expected `type[Self@from_model_type]`, found `type[Model]`
- Found 446 diagnostics
+ Found 448 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:675:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Bus[Any], object_]`, found `InterGetItemILocReduces[Bus[Any] | Bottom[Index[Any]] | Bottom[Series[Any, Any]] | ... omitted 6 union elements, object_ | Self@iloc]`
+ static_frame/core/bus.py:675:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Bus[Any], object_]`, found `InterGetItemILocReduces[Self@iloc | Bus[Any], object_ | Self@iloc]`
- 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/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[Series[Any, Any]] | ndarray[Never, Never] | ... omitted 6 union elements, object_]`
- Found 1823 diagnostics
+ Found 1821 diagnostics

core (https://github.com/home-assistant/core)
- homeassistant/components/xbox/browse_media.py:35:9: error[invalid-argument-type] Argument is incorrect: Expected `type`, found `Literal[MediaClass.APP]`
+ homeassistant/components/xbox/browse_media.py:35:9: error[invalid-argument-type] Argument is incorrect: Expected `type[MediaTypeDetails]`, found `Literal[MediaClass.APP]`
- homeassistant/components/xbox/browse_media.py:39:9: error[invalid-argument-type] Argument is incorrect: Expected `type`, found `Literal[MediaClass.GAME]`
+ homeassistant/components/xbox/browse_media.py:39:9: error[invalid-argument-type] Argument is incorrect: Expected `type[MediaTypeDetails]`, found `Literal[MediaClass.GAME]`

No memory usage changes detected ✅

AlexWaygood

Excellent, thank you!

bxff requested review from AlexWaygood, carljm, dcreager and sharkdp as code owners January 16, 2026 17:58

remove allocation and extend test

2b4ae5d

AlexWaygood approved these changes Jan 16, 2026

View reviewed changes

AlexWaygood enabled auto-merge (squash) January 16, 2026 18:52

AlexWaygood added the ty Multi-file analysis & type inference label Jan 16, 2026

AlexWaygood merged commit 5c97b6e into astral-sh:main Jan 16, 2026
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[ty] Correct return type for synthesized NamedTuple.new methods#22625

[ty] Correct return type for synthesized NamedTuple.new methods#22625
AlexWaygood merged 2 commits intoastral-sh:mainfrom
bxff:fix-namedtuple-new

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bxff commented Jan 16, 2026 •

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`mypy_primer` results