Dead code identified via coverage analysis

[ldayton]

Summary

Coverage analysis reveals 87% coverage on src/parable.py (917 of 7285 lines never hit). Most uncovered code is rare edge cases or defensive fallbacks, but some is provably unreachable.

Command

uv run --with coverage coverage run tests/bin/run-tests.py
uv run --with coverage coverage report --show-missing src/parable.py

Truly Dead Code

Lines	Code	Why Impossible
398-400	ContextStack.get_current()	Method defined but never called
402-404	ContextStack.push()	Method defined but never called
406-410	ContextStack.pop()	Method defined but never called
7858-7859	self.pos = start; return None, "" in _parse_arithmetic_expansion	Loop exits when depth==0 OR at_end(). If depth!=0, must be at_end() → raises MatchedPairError. The return path requires depth!=0 AND NOT at_end(), which is impossible.

Likely Dead (defensive code for impossible internal states)

Lines	Code	Notes
962-966	Param expansion fallback	Called after seeing ${ — should always succeed or raise
1005-1009	Command sub fallback	Called after seeing $(
1021-1025	Deprecated arith fallback	Called after seeing $[
1045-1050	Process sub fallback	Called after seeing <( or >(

Just Untested (rare but valid bash)

• 756-783: POSIX [=x=] equivalence classes and [.x.] collating symbols
• 3406-3440: Bash 5.1+ ${ cmd; } brace command substitution
• 7502-7622: Heredocs inside backtick command substitutions
• Arithmetic to_sexp() methods: Nodes created but serialization not tested

Recommendation

1. Delete ContextStack.get_current(), push(), pop() — unused
2. Delete lines 7858-7859 — unreachable
3. Consider removing defensive fallbacks (962-966, 1005-1009, etc.) or converting to assertions
4. Add tests for ${ cmd; } syntax and POSIX bracket expressions if supporting them