fix: handle templated lambdas in semicolon check by tusharmalpani20 · Pull Request #454 · cpplint/cpplint

tusharmalpani20 · 2026-07-29T18:07:42Z

Fixes #385.

The trailing-semicolon check now recognizes C++20 templated lambdas,
including multiline template parameter lists and requires-clauses.

The existing warnings for operator[] and ordinary constrained function
definitions remain unchanged.

Tests:

pytest — 231 passed, 96.43% coverage
pylint cpplint.py
pre-commit run --all-files
C++20 examples verified with g++ -std=c++20

Summary by CodeRabbit

Bug Fixes
- Fixed false-positive readability warnings for C++20 templated lambdas, including multiline requires clauses.
- Improved handling of multiline lambda syntax to avoid incorrectly flagging valid code for redundant trailing semicolons.
Tests
- Added coverage for templated lambdas with multiline parameters, bodies, and constraints.
Documentation
- Updated the changelog with details of the readability warning fix.

coderabbitai · 2026-07-29T18:08:02Z

📝 Walkthrough

Walkthrough

The change updates trailing-semicolon detection for C++20 templated lambdas, including multiline requires clauses. It adds regression tests and records the fix in the changelog.

Changes

Templated Lambda Detection

Layer / File(s)	Summary
Lambda matching and trailing-semicolon handling `cpplint.py`	New helpers match captures across template and `requires` clauses. `CheckTrailingSemicolon` uses them to avoid false positives while preserving `operator[]` warnings.
Templated lambda regression coverage and changelog `cpplint_unittest.py`, `CHANGELOG.rst`	Adds multiline templated-lambda test cases and documents the corrected braces diagnostic.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant CheckTrailingSemicolon
  participant MatchLambdaCapture
  participant MatchLambdaRequiresClause
  CheckTrailingSemicolon->>MatchLambdaCapture: match lambda capture and template boundary
  MatchLambdaCapture-->>CheckTrailingSemicolon: return capture match
  CheckTrailingSemicolon->>MatchLambdaRequiresClause: inspect multiline requires clause
  MatchLambdaRequiresClause-->>CheckTrailingSemicolon: return preceding capture match

Possibly related PRs

cpplint/cpplint#458: Both changes update CheckTrailingSemicolon and lambda tests for C++20 templated-lambda brace warnings.

🚥 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 templated lambdas in the trailing-semicolon check.
Linked Issues check	✅ Passed	The changes address issue `#385` by preventing false positives after C++20 templated lambdas and adding relevant regression tests.
Out of Scope Changes check	✅ Passed	The implementation, regression tests, and changelog entry are directly related to the linked issue and PR objectives.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

Create PR with unit tests

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

_{Comment @coderabbitai help to get the list of available commands.}

androvonx95

Duplicate — see my other review on this PR.

androvonx95

Reviewed at bce7f59 against current develop.

Fixes the #385 case and the harder valid C++20 forms that a same-line ]<...> check misses — multiline template parameter lists, ]<T> with ( on the next line, and trailing requires-clauses. I compiled those with g++ -std=c++20 -pedantic-errors -fsyntax-only and confirmed they stay clean here while ordinary templated/constrained functions and operator[] (including multiline) still warn. Full unit suite: 206 passed.

This conflicts with #458; I’d take this one — it’s the more complete coverage for the same issue.

coderabbitai

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

cpplint_unittest.py (1)
5787-5793: 🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Assert the diagnostic for foo.cc.

Line 5792 counts bar_header_error, but this invocation lints test/foo.cc. The assertion passes even if including foo.hpp incorrectly reports that foo.cc omitted its related header.
Proposed fix
-            assert error_collector.Results().count(bar_header_error) == 0
+            assert error_collector.Results().count(foo_header_error) == 0
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpplint_unittest.py` around lines 5787 - 5793, Update the assertion in the
multiple-same-basename test to count the diagnostic associated with foo.cc
rather than bar_header_error, while preserving the expectation that including
foo.hpp produces no related-header error for foo.cc. Use the existing diagnostic
symbol or construction for foo.cc from the surrounding test setup.

🧹 Nitpick comments (1)

cpplint_unittest.py (1)

3169-3201: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Add coverage for a trailing lambda requires clause.

The new tests only cover a requires clause before the lambda parameter list. C++20 also permits a clause after the parameter list. A matcher regression in that form will pass this suite.

Proposed test

+        self.TestMultiLineLint(
+            "auto identity = []<typename T>(T&& t)\n"
+            "    requires std::integral<T> &&\n"
+            "             std::copyable<T>\n"
+            "{\n"
+            "  return t;\n"
+            "};\n",
+            "",
+        )

Verify this form with the project C++20 compiler.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpplint_unittest.py` around lines 3169 - 3201, Add a TestMultiLineLint case
alongside the existing generic lambda requires-clause cases covering a trailing
requires clause after the lambda parameter list, including a multiline
constraint if appropriate. Use valid C++20 syntax and verify the test with the
project’s C++20 compiler, expecting no lint errors.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@cpplint_unittest.py`:
- Around line 5787-5793: Update the assertion in the multiple-same-basename test
to count the diagnostic associated with foo.cc rather than bar_header_error,
while preserving the expectation that including foo.hpp produces no
related-header error for foo.cc. Use the existing diagnostic symbol or
construction for foo.cc from the surrounding test setup.

---

Nitpick comments:
In `@cpplint_unittest.py`:
- Around line 3169-3201: Add a TestMultiLineLint case alongside the existing
generic lambda requires-clause cases covering a trailing requires clause after
the lambda parameter list, including a multiline constraint if appropriate. Use
valid C++20 syntax and verify the test with the project’s C++20 compiler,
expecting no lint errors.

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 6381b6bc-67e3-421c-ac55-69ec440f368d

📥 Commits

Reviewing files that changed from the base of the PR and between bce7f59 and fee646d.

📒 Files selected for processing (3)

CHANGELOG.rst
cpplint.py
cpplint_unittest.py

🚧 Files skipped from review as they are similar to previous changes (2)

CHANGELOG.rst
cpplint.py

tusharmalpani20 · 2026-08-02T15:53:32Z

Thanks for the review! I resolved the conflict with current develop in fee646d, preserving both changelog entries. All 231 tests and repository checks pass locally. Could you please take another look when you have time?

androvonx95

Rechecked at fee646d. Merge with current develop looks clean — both changelog entries are preserved, and the templated-lambda logic is unchanged from bcf7f59.

Re-ran the earlier cases against this head: #385, multiline template params, ]<T>n(, and requires-clauses stay clean; templated/constrained functions and multiline operator[] still warn. Full suite: 206 passed. Still LGTM.

yangfan-yf-yf

Reviewed at fee646d.

The matcher keeps ordinary constrained functions and multiline operator[] declarations in the trailing-semicolon path while recognizing the C++20 templated-lambda forms. I also checked a trailing requires-clause lambda and confirmed it stays clean under the repository's brace-style rule.

Verified locally:

python -m pytest --no-cov -q
231 passed

git diff --check upstream/develop...HEAD
Passed

LGTM.

fix: handle templated lambdas in semicolon check

bce7f59

coderabbitai Bot mentioned this pull request Jul 31, 2026

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

Open

androvonx95 approved these changes Aug 2, 2026

View reviewed changes

merge: update templated lambda fix with develop

fee646d

coderabbitai Bot reviewed Aug 2, 2026

View reviewed changes

tusharmalpani20 requested a review from androvonx95 August 2, 2026 15:53

androvonx95 approved these changes Aug 2, 2026

View reviewed changes

yangfan-yf-yf approved these changes Aug 4, 2026

View reviewed changes

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

Looking for more maintainers #402

Open

Navigation Menu

Uh oh!

fix: handle templated lambdas in semicolon check - #454

fix: handle templated lambdas in semicolon check#454
tusharmalpani20 wants to merge 2 commits into
cpplint:developfrom
tusharmalpani20:fix/templated-lambda-semicolon

tusharmalpani20 commented Jul 29, 2026 •

edited by coderabbitai Bot

Loading

Uh oh!

coderabbitai Bot commented Jul 29, 2026 •

edited

Loading

Walkthrough

Changes

Sequence Diagram(s)

Uh oh!

androvonx95 left a comment •

edited

Loading

Uh oh!

androvonx95 left a comment

Uh oh!

coderabbitai Bot left a comment

Uh oh!

tusharmalpani20 commented Aug 2, 2026

Uh oh!

androvonx95 left a comment

Uh oh!

yangfan-yf-yf left a comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

tusharmalpani20 commented Jul 29, 2026 • edited by coderabbitai Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary by CodeRabbit

Uh oh!

coderabbitai Bot commented Jul 29, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Changes

Sequence Diagram(s)

Uh oh!

androvonx95 left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

androvonx95 left a comment

Choose a reason for hiding this comment

Uh oh!

coderabbitai Bot left a comment

Choose a reason for hiding this comment

Uh oh!

tusharmalpani20 commented Aug 2, 2026

Uh oh!

androvonx95 left a comment

Choose a reason for hiding this comment

Uh oh!

yangfan-yf-yf left a comment

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

tusharmalpani20 commented Jul 29, 2026 •

edited by coderabbitai Bot

Loading

coderabbitai Bot commented Jul 29, 2026 •

edited

Loading

androvonx95 left a comment •

edited

Loading