Prevent comma abuse by implementing new rule

[jgengo]

Fix: Detect comma operator abuse to bypass line count rules

Issues Fixed

• Fixes comma operator loophole allowing students to bypass 25-line function limit
• Prevents chaining multiple function calls/assignments on a single line using comma operators

Problem

Students were exploiting comma operators wrapped in parentheses to bypass the 25-line function limit and "too many instructions" rules:

(free(a), free(b), free(c), free(d), free(e));
return (free(a), free(b), free(c), 0);

These expressions passed validation despite chaining multiple function calls on a single line.

Solution

• Added new rule CheckCommaOperatorAbuse that detects multiple function calls or assignments chained with comma operators within parentheses
• Introduced COMMA_OP_ABUSE error type with message: "Comma operator used to chain multiple function calls or assignments"
• Rule correctly distinguishes between abuse and legitimate comma usage (function parameters, for-loop expressions)

Verification Steps

Please ensure the following steps have been completed:

• Added new tests to cover the changes.
  • Added tests/rules/samples/ko_comma_operator_abuse.c (negative test)
  • Added tests/rules/samples/ok_comma_in_params.c (positive test)
• Fixed all broken tests.
  • All 517 tests passing
• Ran poetry run flake8 to check for linting issues.
  • No linting issues found
• Verified that all unit tests are passing:
  • Ran poetry run pytest to ensure unit tests pass (517/517 passed).
  • Ran poetry run tox to validate compatibility across Python versions.

Testing Results

• ✅ Original abuse cases now caught and flagged with COMMA_OP_ABUSE error
• ✅ Legitimate comma usage still allowed:
  • Function parameters: printf("%d %d", a, b) → OK
  • For-loop expressions → OK
• ✅ All 517 existing tests pass with no regressions
• ✅ New test cases validate both positive and negative scenarios

Files Changed

• norminette/rules/check_comma_operator_abuse.py (new, 155 lines)
• norminette/norm_error.py (modified, +1 error definition)
• tests/rules/samples/ko_comma_operator_abuse.c (new)
• tests/rules/samples/ko_comma_operator_abuse.out (new)
• tests/rules/samples/ok_comma_in_params.c (new)
• tests/rules/samples/ok_comma_in_params.out (new)

Additional Notes

The new rule scans for opening parentheses and counts:

1. Top-level comma operators within the parentheses
2. Function calls (IDENTIFIER followed by LPARENTHESIS pattern)
3. Assignment operators

If 2+ function calls or 2+ assignments are chained with commas, the rule flags a COMMA_OP_ABUSE error.

The implementation properly handles nested parentheses to avoid false positives on legitimate patterns like func(a, func2(b, c)).

[NiumXp]

Hello, @jgengo!

Can you add tests for (ab(a(), b())) and ((f)(), f())?