[ty] Recognize functions with stub bodies in `Protocol` classes as implicitly abstract by AlexWaygood · Pull Request #22838 · astral-sh/ruff

AlexWaygood · 2026-01-24T17:26:18Z

Summary

We now consider any method in a Protocol class to be implicitly abstract if the Protocol class is defined in a .py file and of the following conditions is met regarding the method:

It has a "stub body" (all statements are docstrings, ... or pass), and they have a return type that is not assignable to None
It has a body that only consists of raise NotImplementedError, and it has a return type that is not assignable to Never

We also now do not emit abstract-method-in-final-class for @final Protocol classes. Unlike non-Protocol classes, it is possible to subtype a Protocol class without explicitly subclassing it, so an @final Protocol class with unimplemented abstract methods is not inherently broken in the same way as an @final non-Protocol class.

Test Plan

mdtests and snapshots

astral-sh-bot · 2026-01-24T17:27:59Z

Typing conformance results

No changes detected ✅

astral-sh-bot · 2026-01-24T17:29:14Z

`mypy_primer` results

Changes were detected when running on open source projects

trio (https://github.com/python-trio/trio)
- src/trio/_highlevel_ssl_helpers.py:120:6: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
+ src/trio/_highlevel_ssl_helpers.py:120:6: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Never`

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

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/infrastructure/provisioners/container_instance.py:217:45: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `str`
+ src/prefect/infrastructure/provisioners/container_instance.py:217:45: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- src/prefect/server/events/stream.py:168:54: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
+ src/prefect/server/events/stream.py:168:54: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Never`
- src/prefect/server/services/base.py:104:36: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
+ src/prefect/server/services/base.py:104:36: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Never`
- src/prefect/tasks.py:1801:31: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
+ src/prefect/tasks.py:1801:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Never`
- src/prefect/tasks.py:1827:24: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
+ src/prefect/tasks.py:1827:24: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Never`

django-stubs (https://github.com/typeddjango/django-stubs)
- mypy_django_plugin/config.py:46:57: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
+ mypy_django_plugin/config.py:46:57: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Never`

static-frame (https://github.com/static-frame/static-frame)
- static_frame/core/bus.py:645:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemLocReduces[Bus[Any], object_]`, found `InterGetItemLocReduces[Bottom[Bus[Any]] | Bottom[Series[Any, Any]] | TypeBlocks | ... omitted 6 union elements, object_]`
- static_frame/core/bus.py:649:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Bus[Any], object_]`, found `InterGetItemILocReduces[Bottom[Bus[Any]] | IndexHierarchy | TypeBlocks | ... omitted 7 union elements, Self@iloc]`
+ static_frame/core/bus.py:649:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[Bus[Any], object_]`, found `InterGetItemILocReduces[Self@iloc, Self@iloc]`
- 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[Bottom[Series[Any, Any]] | Bottom[Index[Any]] | ndarray[Never, Never] | ... omitted 7 union elements, TVDtype@Series]`
- static_frame/core/series.py:4072:16: error[invalid-return-type] Return type does not match returned value: expected `InterGetItemILocReduces[SeriesHE[Any, Any], TVDtype@SeriesHE]`, found `InterGetItemILocReduces[Bottom[Series[Any, Any]] | Bottom[Index[Any]] | TypeBlocks | ... omitted 7 union elements, TVDtype@SeriesHE]`
- 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[Bottom[Yarn[Any]] | IndexHierarchy | TypeBlocks | ... omitted 7 union elements, object_]`
- Found 1830 diagnostics
+ Found 1826 diagnostics

streamlit (https://github.com/streamlit/streamlit)
- lib/streamlit/commands/execution_control.py:136:6: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
- lib/streamlit/commands/execution_control.py:192:6: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
- Found 95 diagnostics
+ Found 93 diagnostics

ibis (https://github.com/ibis-project/ibis)
- ibis/backends/bigquery/__init__.py:455:10: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Backend`
+ ibis/backends/bigquery/__init__.py:455:10: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Backend`

pandas-stubs (https://github.com/pandas-dev/pandas-stubs)
- tests/frame/test_groupby.py:229:15: error[type-assertion-failure] Type `Series[Any]` does not match asserted type `Series[str | bytes | int | ... omitted 12 union elements]`
- tests/frame/test_groupby.py:625:15: error[type-assertion-failure] Type `Series[Any]` does not match asserted type `Series[str | bytes | int | ... omitted 12 union elements]`
- Found 4415 diagnostics
+ Found 4413 diagnostics

No memory usage changes detected ✅

astral-sh-bot · 2026-01-24T17:35:49Z

`ecosystem-analyzer` results

Lint rule	Added	Removed	Changed
`empty-body`	0	10	0
`invalid-return-type`	8	0	1
`invalid-parameter-default`	0	0	7
`invalid-argument-type`	1	2	3
`invalid-assignment`	0	0	4
`unused-type-ignore-comment`	2	0	0
Total	11	12	15

Full report with detailed diff (timing results)

crates/ty_python_semantic/resources/mdtest/final.md

crates/ty_python_semantic/src/types/function.rs

charliermarsh

I think I personally would've expected def also_not_abstractmethod(self) -> None: ... to be considered implicitly abstract (but could understand why def also_not_abstractmethod(self) -> None: pass might not) just based on some argument around "programmer intent". Your approach is also reasonable though, that opinion is highly subjective.

crates/ty_python_semantic/src/types/class.rs

crates/ty_python_semantic/src/types/function.rs

crates/ty_python_semantic/src/types/class.rs

crates/ty_python_semantic/resources/mdtest/final.md

AlexWaygood · 2026-01-29T15:46:32Z

Alright, I've switched the behaviour to match that of other type checkers, and made the Salsa caching more fine-grained so that we don't over-invalidate the ClassType::abstract_methods query when the AST changes in another file. I'd appreciate another once-over from somebody, since it's now quite a big PR and the code's changed a fair amount since the last round of review 😄

AlexWaygood · 2026-01-29T15:57:10Z

streamlit (https://github.com/streamlit/streamlit)
- lib/streamlit/commands/execution_control.py:136:6: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
- lib/streamlit/commands/execution_control.py:192:6: error[empty-body] Function always implicitly returns `None`, which is not assignable to return type `Never`
- Found 95 diagnostics
+ Found 93 diagnostics

These diagnostics are going away because the error code is changing from empty-body to invalid-return-type (which seems correct; not sure why it was empty-body before), and they have # ty: ignore[invalid-return-type] on the function, which suppresses the new invalid-return-type error.

carljm

Looks great!

crates/ty_python_semantic/resources/mdtest/final.md

Co-authored-by: Carl Meyer <[email protected]>

AlexWaygood added the ty Multi-file analysis & type inference label Jan 24, 2026

AlexWaygood added the ecosystem-analyzer label Jan 24, 2026

AlexWaygood force-pushed the alex/trivial-bodies branch 4 times, most recently from 728fc6f to 5a0043b Compare January 24, 2026 18:12

AlexWaygood commented Jan 24, 2026

View reviewed changes

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

AlexWaygood requested a review from charliermarsh January 24, 2026 18:42

AlexWaygood marked this pull request as ready for review January 24, 2026 18:43

AlexWaygood requested review from carljm, dcreager and sharkdp as code owners January 24, 2026 18:43

charliermarsh reviewed Jan 24, 2026

View reviewed changes

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

charliermarsh reviewed Jan 24, 2026

View reviewed changes

crates/ty_python_semantic/src/types/function.rs Show resolved Hide resolved

charliermarsh approved these changes Jan 24, 2026

View reviewed changes

AlexWaygood force-pushed the alex/trivial-bodies branch from 5a0043b to 0baf26b Compare January 24, 2026 23:44

AlexWaygood commented Jan 26, 2026

View reviewed changes

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

AlexWaygood force-pushed the alex/trivial-bodies branch from 0baf26b to 718fce8 Compare January 27, 2026 18:44

carljm reviewed Jan 28, 2026

View reviewed changes

AlexWaygood added 2 commits January 29, 2026 14:47

Extract determination of whether a function has a stub body

4dbfe32

recognize stub functions in Protocol classes as implicitly abstract

91b021b

AlexWaygood force-pushed the alex/trivial-bodies branch from 718fce8 to 86f5ce8 Compare January 29, 2026 15:17

review comments

ee7a9ac

AlexWaygood force-pushed the alex/trivial-bodies branch from 86f5ce8 to ee7a9ac Compare January 29, 2026 15:19

AlexWaygood added 3 commits January 29, 2026 15:36

match mypy's subdiagnostics

c60be2f

ytpe is probably a Welsh village somewhere

810016e

.

5584031

AlexWaygood force-pushed the alex/trivial-bodies branch from 0be310b to 5584031 Compare January 29, 2026 15:41

AlexWaygood requested a review from carljm January 29, 2026 15:46

carljm approved these changes Jan 31, 2026

View reviewed changes

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

Update crates/ty_python_semantic/resources/mdtest/final.md

24295af

Co-authored-by: Carl Meyer <[email protected]>

AlexWaygood force-pushed the alex/trivial-bodies branch from 677daaa to 24295af Compare January 31, 2026 09:52

AlexWaygood enabled auto-merge (squash) January 31, 2026 09:53

AlexWaygood merged commit 2ff4748 into main Jan 31, 2026
48 checks passed

AlexWaygood deleted the alex/trivial-bodies branch January 31, 2026 10:02

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

[ty] Recognize functions with stub bodies in `Protocol` classes as implicitly abstract#22838

[ty] Recognize functions with stub bodies in `Protocol` classes as implicitly abstract#22838
AlexWaygood merged 7 commits intomainfrom
alex/trivial-bodies

AlexWaygood commented Jan 24, 2026 •

edited

Loading

Uh oh!

astral-sh-bot bot commented Jan 24, 2026 •

edited

Loading

Uh oh!

astral-sh-bot bot commented Jan 24, 2026 •

edited

Loading

Uh oh!

astral-sh-bot bot commented Jan 24, 2026 •

edited

Loading

Uh oh!

Uh oh!

Uh oh!

Uh oh!

charliermarsh left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

AlexWaygood commented Jan 29, 2026

Uh oh!

AlexWaygood commented Jan 29, 2026

Uh oh!

carljm left a comment

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Conversation

AlexWaygood commented Jan 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Test Plan

Uh oh!

astral-sh-bot bot commented Jan 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Typing conformance results

Uh oh!

astral-sh-bot bot commented Jan 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

mypy_primer results

Uh oh!

astral-sh-bot bot commented Jan 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

ecosystem-analyzer results

Uh oh!

Uh oh!

Uh oh!

Uh oh!

charliermarsh left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

AlexWaygood commented Jan 29, 2026

Uh oh!

AlexWaygood commented Jan 29, 2026

Uh oh!

carljm left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

AlexWaygood commented Jan 24, 2026 •

edited

Loading

astral-sh-bot bot commented Jan 24, 2026 •

edited

Loading

astral-sh-bot bot commented Jan 24, 2026 •

edited

Loading

`mypy_primer` results

astral-sh-bot bot commented Jan 24, 2026 •

edited

Loading

`ecosystem-analyzer` results