Issue #23: allow comments and blank lines in rule files

[HoldenHrabak]

Summary

Fixes #23.

parseRules() in mutator.py already silently ignored lines starting with #, but only under three conditions: no leading whitespace, the line was not exactly "\n", and the line did not contain ==>. Indented comments ( # note) and whitespace-only blank lines both triggered a spurious DOES NOT MATCH EXPECTED FORMAT warning. This PR fixes that and documents the feature so users can confidently use comments to organise their rule sets.

Changes

• universalmutator/mutator.py — rewrote the comment/blank-line branch of parseRules so the # / empty check runs on the stripped line. The ==> check still runs first, which preserves two existing rules whose LHS legitimately starts with #:
  • #include ==> DO_NOT_MUTATE in static/c_like.rules
  • # ==> SKIP_MUTATING_REST in static/python.rules
• tests/test_rule_comments.py — new file, 9 unit tests covering:
  • plain #, indented #, tab-indented #
  • empty and whitespace-only blank lines
  • both legacy #-prefixed rules (regression tests)
  • a realistic mixed-content header
  • malformed-line warning still fires
• universalmutator/static/universal.rules — added an 8-line header that documents the rules-file format and serves as a live demo that the parser accepts it.
• README.md — new "Rule Files" section covering the syntax and the comment behaviour.

Scope

Deliberately full-line comments only. Inline comments (foo ==> bar # note) would be nice but are ambiguous — # is a legal regex character, and stripping anything after # in the RHS would silently change the behaviour of any rule a user has written that depends on a literal #. Happy to follow up with a separate PR if that trade-off is acceptable; this one is scoped to the unambiguous case.

Testing

All tests pass locally on Python 3.12:

$ pytest tests/
========================= 10 passed in 55s =========================

The existing test_foo_example.py exercises parseRules end-to-end through the mutate / analyze_mutants / prioritize_mutants CLI pipeline and continues to pass with the header comments now present in universal.rules, confirming no behavioural change in the generated-mutant count.

Diff stats

 README.md                               |  24 ++++++
 tests/test_rule_comments.py             | 144 ++++++++++++++++++++++++++++++++
 universalmutator/mutator.py             |  36 ++++----
 universalmutator/static/universal.rules |  10 +++
 4 files changed, 199 insertions(+), 15 deletions(-)

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cc @ClassProg (submitting as a class project)