Added check for valid representation invariant syntax

[KushGandhi3]

Proposed Changes

Adds a new custom checker invalid-representation-invariant-syntax (E9982) that reports when a class's representation invariants in its docstring contain invalid Python expression syntax. Previously, such invariants were silently skipped at runtime by python_ta.contracts._set_invariants, hiding likely typos (e.g. self.x !== 0, self.x = 5) from students.

The new checker mirrors the existing invalid-precondition-syntax (E9980) and invalid-postcondition-syntax (E9981) checks, but runs on class definitions via a new visit_classdef hook in ContractChecker. It reuses the existing parse_assertions helper with parse_token="Representation Invariant", which is the same token used by the runtime, to keep static and runtime behaviour aligned. Each invariant is whitespace-normalized (so multi-line RIs joined with \ are handled) and fed to ast.parse(..., mode="eval"); a SyntaxError emits the new message.

Closes #1303. This is the final sub-issue of #1293 ("Create checkers for contract syntax"); with #1294 and #1302 already merged, the parent issue will be fully addressed once this PR lands.

Screenshots of your changes (if applicable)

Type of Change

Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)	X
🐛 Bug fix (non-breaking change that fixes an issue)
♻️ Refactoring (internal change to codebase, without changing functionality)
🚦 Test update (change that only adds or modifies tests)
📚 Documentation update (change that only updates documentation)
📦 Dependency update (change that updates a dependency)
🔧 Internal (change that only affects developers or continuous integration)

Checklist

Before opening your pull request:

• I have performed a self-review of my changes.
  • Check that all changed files included in this pull request are intentional changes.
  • Check that all changes are relevant to the purpose of this pull request, as described above.
• I have added tests for my changes, if applicable.
  • This is required for all bug fixes and new features.
• I have updated the project documentation, if applicable.
  • This is required for new features.
• I have updated the project Changelog (this is required for all changes).
• If this is my first contribution, I have added myself to the list of contributors.

After opening your pull request:

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Questions and Comments

(Include any questions or comments you have regarding your changes.)

[KushGandhi3]

Hi Professor Liu (@david-yz-liu), could you please approve the workflow run? CI seems to be gated as this is my first contribution to the repo. I'd request a review directly as well, but the option isn't available to non-collaborators. Thanks!

[KushGandhi3]

Hi Professor @david-yz-liu, I looked into the CI failure and it seems to be a flaky timeout in packages/python-ta/tests/test_reporters/test_html_server.py::test_websocket_message, not an issue caused by my PR.

This test sometimes races between the WebSocket server starting and watchdog fully attaching the file watcher. If the file change happens a little too early, the reload event gets missed and ws.recv() times out. My PR only adds the new invalid-representation-invariant-syntax checker (E9982) plus related tests and docs. It does not change the HTML server, WebSocket logic, watch mode, or dependencies used by this test.

[KushGandhi3]

Hi Professor @david-yz-liu,

I wanted to follow up on PR #1334. The PR now has a newer head commit, and the latest PythonTA Tests workflow is showing action_required, so the jobs have not started and Coveralls has not produced a current report.

For context, the earlier CI run did execute; the only failure was packages/python-ta/tests/test_reporters/test_html_server.py::test_websocket_message in the Python 3.12/base job, while the rest of the matrix, docs, and prek passed. My PR only adds the E9982 representation-invariant syntax checker plus its tests/docs/example, and does not touch the HTML server, WebSocket/watch-mode code, or dependencies.

Could you please approve the latest workflow run when you have a chance? If the same WebSocket test flakes again, would it be possible to rerun the failed job?

Thank you!

[david-yz-liu]

Thanks very much, @KushGandhi3! I've been a bit busy and haven't had a chance to review this until now, but you did great work here. 👍

[coveralls]

Coverage Report for CI Build 25408942332

Coverage increased (+0.03%) to 90.023%

Details

• Coverage increased (+0.03%) from the base build.
• Patch coverage: 11 of 11 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	3879
Covered Lines:	3492
Line Coverage:	90.02%
Coverage Strength:	17.46 hits per line

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💛 - Coveralls