fix(braces): exempt C++20 templated lambdas from trailing-semicolon check by breidenbach0 · Pull Request #458 · cpplint/cpplint · GitHub

Fixes #385.

Problem: a C++20 templated lambda like []<typename T>(T&& t) { ... }; was falsely flagged readability/braces — "You don't need a ; after a }."

Cause: CheckTrailingSemicolon exempts lambdas by checking that the text before ( ends in ] (the capture). A templated lambda puts <T> between ] and (, so the prefix ends in > and the exemption missed it.

Fix: also recognise the ]<...> lambda introducer.

Testing:

templated lambdas ([]<T>, [&]<T>, multi-param, multi-line, []<auto>) → no longer flagged
non-templated lambda → still exempted (unchanged)
real redundant ; (function / for / while / if, including a templated function) → still flagged
pytest cpplint_unittest.py → 206 passed; the new regression tests fail without the fix.

Summary by CodeRabbit

Bug Fixes
- Fixed false redundant trailing semicolon warnings for C++20 templated lambdas.
- Preserved warnings for ordinary templated functions with redundant trailing semicolons.
Tests
- Added coverage for single-line and multi-line C++20 templated lambda expressions.
Documentation
- Updated the changelog with details of the warning fix.

…heck A C++20 templated lambda like []<typename T>(T&& t) { ... }; was falsely flagged with readability/braces 'You don't need a ; after a }'. The lambda exemption relied on the text before '(' ending in ']' (the capture), but a template parameter list sits between ']' and '(' so the prefix ends in '>' and the exemption missed it. Also recognize the ]<...> introducer. Fixes cpplint#385

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Reviewing files that changed from the base of the PR and between bb2f8a6 and c6a64d4.

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CHANGELOG.rst
cpplint.py
cpplint_unittest.py

📝 Walkthrough

Walkthrough

The trailing-semicolon check now suppresses false warnings for C++20 templated lambdas. Regression tests cover single-line and multi-line lambdas and retain warnings for ordinary templated functions. The changelog documents the fix.

Changes

Templated Lambda Semicolon Handling

Layer / File(s)	Summary
Trailing-semicolon detection and regression coverage cpplint.py, cpplint_unittest.py, CHANGELOG.rst	The checker excludes lambda/template-call expressions from redundant trailing-semicolon warnings. Tests cover valid C++20 templated lambdas and preserve warnings for redundant semicolons after templated functions. The changelog records the fix.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

cpplint/cpplint#454: Both changes modify CheckTrailingSemicolon and related templated-lambda tests.

Suggested reviewers: aaronliu0130, janmarsino98

🚥 Pre-merge checks | ✅ 5 ✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the fix for C++20 templated lambdas and the trailing-semicolon check.
Linked Issues check	✅ Passed	The change fixes issue #385 by exempting C++20 templated lambdas while retaining warnings for redundant semicolons elsewhere.
Out of Scope Changes check	✅ Passed	The changelog, implementation, and regression tests directly support the linked issue and PR objective.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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Reviewed at c6a64d4 against current develop.

The same-line / simple multi-line-body cases are fixed, including the exact #385 example, and a templated function still warns. Full suite: 206 passed.

The \\s*<.*>\\s*$ check only looks at the text before ( on that line, so these valid forms still emit readability/braces here (clean on #454):

auto identity = []<
    typename T
>(T&& t) { return t; };

auto identity = []
<typename T>
(T&& t) { return t; };

auto identity = []<typename T>
(T&& t) { return t; };

auto identity = []<typename T>
    requires std::integral<T>
(T&& t) { return t; };

Each compiles under g++ -std=c++20 -pedantic-errors -fsyntax-only. Given the overlap/conflict with #454, I’d lean toward closing this in favor of that PR unless you extend coverage to the multiline/requires cases.

I independently rechecked c6a64d4 and confirmed that the multiline template and requires-clause cases already reported in the existing review still emit readability/braces on this head, while #454 handles the same inputs and preserves diagnostics for multiline operator[] declarations and constrained functions. Since the two PRs overlap and conflict, I don't think this narrower implementation should merge as-is. Unless this branch is broadened beyond #454, I recommend closing it in favor of #454.

breidenbach0 and others added 2 commits July 29, 2026 14:48

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

c6a64d4

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androvonx95 mentioned this pull request Aug 2, 2026

fix: handle templated lambdas in semicolon check #454

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androvonx95 reviewed Aug 2, 2026

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yangfan-yf-yf suggested changes Aug 9, 2026

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yangfan-yf-yf mentioned this pull request Aug 9, 2026

Looking for more maintainers #402

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fix(braces): exempt C++20 templated lambdas from trailing-semicolon check by breidenbach0 · Pull Request #458 · cpplint/cpplint · GitHub

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fix(braces): exempt C++20 templated lambdas from trailing-semicolon check - #458

fix(braces): exempt C++20 templated lambdas from trailing-semicolon check#458
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fix(braces): exempt C++20 templated lambdas from trailing-semicolon check by breidenbach0 · Pull Request #458 · cpplint/cpplint · GitHub

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fix(braces): exempt C++20 templated lambdas from trailing-semicolon check - #458

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