astral-sh/ruff

Which bare tuples are in scope for COM818?

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#18851 opened on Jun 21, 2025

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Description

Summary

trailing-comma-on-bare-tuple (COM818) is documented as:

Checks for the presence of trailing commas on bare (i.e., unparenthesized) tuples.

but it only checks for a comma before a statement-final newline. The documentation should be more precise as to which bare tuples are in scope for this rule.

Bare tuples in subscripts are subject to incorrectly-parenthesized-tuple-in-subscript (RUF031). They are out of scope for COM818.

COM818 does not check bare tuples in yield expressions. Maybe it should, or maybe this should be called out as another exception in the documentation.

def f(x): x.append((yield x[-1],))

COM818 should also check for a comma before a semicolon, as in this bare tuple:

print("Hello,"),;

Version

ruff 0.12.0 (87f0feb21 2025-06-17)

Contributor guide

Tech stack
rustpython
Domain
tooling
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust development setupfamiliarity with Ruff's rule implementation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Review the COM818 rule implementation in the Ruff source code, likely in `crates/ruff linter/src/rules/pycodestyle/rules/trailing comma on bare tuple.rs`. Update the documentation in the rule's docstring and the generated documentation to accurately describe which bare tuples are checked. Test the changes by running the existing test suite and possibly adding new test cases for the semicolon and yield scenarios mentioned in the issue.