Match CPython class generator syntax error

[youknowone]

RustPython uses the parser diagnostic text for SyntaxError. CPython reports invalid syntax for an unparenthesized generator expression in a class base, while calls retain the more specific generator-parenthesization diagnostic.

This makes the class-definition diagnostic context-specific and updates the parser snapshot.

Assisted-by: Codex:GPT-5

Summary by CodeRabbit

• Bug Fixes
  • Improved syntax error reporting for unparenthesized generator expressions in class definitions.
  • Preserved the existing, more specific error message for generator expressions used in function calls.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c7df0d69-d25d-40f4-bad8-1e4368bc19c4

📥 Commits

Reviewing files that changed from the base of the PR and between fa9dfbb and 079f915.

⛔ Files ignored due to path filters (1)

• crates/ruff_python_parser/tests/snapshots/invalid_syntax@class_def_unparenthesized_generator_argument.py.snap is excluded by !**/*.snap

📒 Files selected for processing (1)

• crates/ruff_python_parser/src/parser/expression.rs

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The parser now reports UnparenthesizedGeneratorExpression for call arguments and OtherError("invalid syntax") for class-definition arguments.

Changes

Generator expression error handling

Layer / File(s)	Summary
Context-aware argument validation crates/ruff_python_parser/src/parser/expression.rs	validate_arguments keeps the existing error for ArgumentsContext::Call and reports OtherError("invalid syntax") for ArgumentsContext::ClassDefinition.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 079f9

The change only adjusts the syntax-error message for an already-invalid class base while preserving the existing behavior for call expressions. No actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: dhruvmanila, michareiser

🚥 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 main change: matching CPython's syntax error for generator expressions in class definitions.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch rustpython-class-base-syntax

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