Add new checker and `bare-name-capture-pattern` message #10424

mbyrnepr2 · 2025-06-11T18:46:56Z

Type of Changes

	Type
	🐛 Bug fix
✓	✨ New feature
	🔨 Refactoring
	📜 Docs

Description

This will emit an error message when a name capture pattern is used in a match statement which would make the remaining patterns unreachable. This code is a SyntaxError at runtime.

Closes #7128

codecov · 2025-06-11T19:02:07Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.85%. Comparing base (707323a) to head (c42f8cb).
⚠️ Report is 31 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10424      +/-   ##
==========================================
- Coverage   95.86%   95.85%   -0.02%     
==========================================
  Files         176      177       +1     
  Lines       19155    19199      +44     
==========================================
+ Hits        18363    18403      +40     
- Misses        792      796       +4

Files with missing lines	Coverage Δ
pylint/checkers/match_statements_checker.py	`100.00% <100.00%> (ø)`

... and 9 files with indirect coverage changes

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doc/user_guide/checkers/features.rst

DanielNoord

Nice check!

pylint/checkers/match_statements_checker.py

DanielNoord

Seems very sensible to me!

doc/user_guide/checkers/features.rst

pylint/checkers/match_statements_checker.py

doc/data/messages/u/unreachable-match-patterns/bad.py

Pierre-Sassoulas

Let's put this in 4.0 once the remarks are handled !

pylint/checkers/match_statements_checker.py

.pre-commit-config.yaml

``unreachable-match-patterns``. This will emit an error message when a name capture pattern is used in a match statement which would make the remaining patterns unreachable. This code is a SyntaxError at runtime. Closes pylint-dev#7128

for more information, see https://pre-commit.ci

… 3.10 or higher.

Co-authored-by: Jacob Walls <[email protected]>

ID. (pylint/script/get_unused_message_id_category.py).

text in the checker code.

The example intentionally contains a `SyntaxError` which will also raise a `SyntaxError` from Ruff.

Co-authored-by: Pierre Sassoulas <[email protected]>

doc/data/ruff.toml

Co-authored-by: Pierre Sassoulas <[email protected]>

Pierre-Sassoulas

Great work ! I'll let @jacobtylerwalls merge

Co-authored-by: Jacob Walls <[email protected]>

cdce8p

Thanks for working on it @mbyrnepr2! This looks like a great addition.

I saw the discussion where the error should be emitted. Just to provide one more data point, pylance has a similar error message: Irrefutable pattern is allowed only for the last case statement which is emitted for the cases which currently trigger the check.

There is also another message Pattern will never be matched for subject type "Never" for the second and third cases but that's likely based on the type inference result.

pylint/checkers/match_statements_checker.py

tests/functional/b/bare_name_capture_pattern.py

doc/data/messages/b/bare-name-capture-pattern/bad.py

doc/data/messages/b/bare-name-capture-pattern/good.py

doc/data/ruff.toml

Co-authored-by: Marc Mueller <[email protected]>

cdce8p

This looks good now. Just pushed one more change to improve the error location c42f8cb. Thanks @mbyrnepr2 👍🏻

github-actions · 2025-08-14T20:56:54Z

🤖 According to the primer, this change has no effect on the checked open source code. 🤖🎉

This comment was generated for commit c42f8cb

Pierre-Sassoulas added the Enhancement ✨ Improvement to a component label Jun 11, 2025

mbyrnepr2 commented Jun 12, 2025

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mbyrnepr2 force-pushed the 7128_remaining_patterns_unreachable branch from f1ca097 to 0e5ef7c Compare June 12, 2025 08:54

mbyrnepr2 changed the title ~~Add remaining-patterns-unreachable checker.~~ Add unreachable-match-patterns message and new checker. Jun 12, 2025

mbyrnepr2 marked this pull request as ready for review June 12, 2025 14:32

DanielNoord reviewed Jun 16, 2025

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DanielNoord previously approved these changes Jun 17, 2025

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Pierre-Sassoulas added this to the 4.0.0 milestone Jun 17, 2025

jacobtylerwalls reviewed Jul 27, 2025

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pylint/checkers/match_statements_checker.py Outdated Show resolved Hide resolved

doc/data/messages/u/unreachable-match-patterns/bad.py Outdated Show resolved Hide resolved

Pierre-Sassoulas reviewed Aug 2, 2025

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mbyrnepr2 dismissed DanielNoord’s stale review via c9fbf52 August 2, 2025 13:24

Pierre-Sassoulas previously approved these changes Aug 2, 2025

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mbyrnepr2 dismissed Pierre-Sassoulas’s stale review via 6670963 August 2, 2025 14:11

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Pierre-Sassoulas reviewed Aug 3, 2025

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.pre-commit-config.yaml Outdated Show resolved Hide resolved

mbyrnepr2 and others added 12 commits August 3, 2025 14:39

[pre-commit.ci] auto fixes from pre-commit.com hooks

131fe47

for more information, see https://pre-commit.ci

Remove the trailing / from the url.

af24ce1

Remove the unnecessary logic which checks if the version of Python is…

b3e8f2d

… 3.10 or higher.

Remove unnecessary .rc file from the functional test.

50590cd

Update pylint/checkers/match_statements_checker.py

aabe71c

Co-authored-by: Jacob Walls <[email protected]>

Update doc/user_guide/checkers/features.rst

e2c5ed9

Co-authored-by: Jacob Walls <[email protected]>

Update the message ID using the script which finds the next available

a62ca0f

ID. (pylint/script/get_unused_message_id_category.py).

Update the functional test output in response to the modified message

7681772

text in the checker code.

Exclude doc example from Ruff.

cc1f227

The example intentionally contains a `SyntaxError` which will also raise a `SyntaxError` from Ruff.

Update .pre-commit-config.yaml

68aaf34

Co-authored-by: Pierre Sassoulas <[email protected]>

Exclude the example code documentation via ruff.toml instead.

26a0f0a

mbyrnepr2 force-pushed the 7128_remaining_patterns_unreachable branch from ad3ec16 to 26a0f0a Compare August 3, 2025 12:42

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Pierre-Sassoulas reviewed Aug 3, 2025

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mbyrnepr2 and others added 2 commits August 4, 2025 09:28

Change the name of the message.

43b300a

Move the ruff config line underneath a helpful comment.

e55b3a6

Co-authored-by: Pierre Sassoulas <[email protected]>

mbyrnepr2 changed the title ~~Add unreachable-match-patterns message and new checker.~~ Add new checker and bare-name-capture-pattern message. Aug 4, 2025

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Pierre-Sassoulas previously approved these changes Aug 7, 2025

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Update the wording of the new message.

0d9c4b5

Co-authored-by: Jacob Walls <[email protected]>

mbyrnepr2 dismissed Pierre-Sassoulas’s stale review via 0d9c4b5 August 8, 2025 18:03

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cdce8p requested changes Aug 9, 2025

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Apply suggestions from code review

034d78f

Co-authored-by: Marc Mueller <[email protected]>

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Improve error location

c42f8cb

cdce8p changed the title ~~Add new checker and bare-name-capture-pattern message.~~ Add new checker and bare-name-capture-pattern message Aug 14, 2025

cdce8p approved these changes Aug 14, 2025

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Pierre-Sassoulas approved these changes Aug 14, 2025

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cdce8p merged commit b6ac272 into pylint-dev:main Aug 14, 2025
44 checks passed

cdce8p temporarily deployed to Backport August 14, 2025 21:07 — with GitHub Actions Inactive

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Add new checker and bare-name-capture-pattern message #10424

Add new checker and bare-name-capture-pattern message #10424

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mbyrnepr2 commented Jun 11, 2025

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Add new checker and `bare-name-capture-pattern` message #10424

Add new checker and `bare-name-capture-pattern` message #10424

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