perf(coverage): stop forking grep per source line in the report phase - #1031
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Profiling --coverage showed the report, not the capture engine, was half
the wall time and identical for both engines: is_executable_line fell back
to a `grep -E` fork for every line it could not classify in pure Bash, and
every tracked line is classified twice per run (precompute_file_stats, then
report_lcov). 286 source lines cost 1055 grep forks.
The combined regex is replaced by `case` globs reproducing it exactly,
quirks included: inside a POSIX bracket expression a backslash is a literal
member of the set, so `[^\)]` also excludes `\` and `[\{\}]` also matches a
bare line continuation. Verified by running both implementations over the
same 41173 lines across 395 files on Bash 3.2 and 5.3 with zero
disagreements, with the differential harness mutation-tested.
Also surfaces the engine: --verbose reports the one in use, and an explicit
BASHUNIT_COVERAGE_ENGINE=xtrace that the running Bash cannot honour now
warns instead of being dropped silently — the common case on macOS.
Coverage totals are unchanged and still match between --parallel and
sequential for each engine.
Closes #1005
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🤔 Background
Related #1005
Profiling
--coveragebefore optimising anything showed the cost is not where the issue assumed. The report phase is ~50-60% of wall time and is identical for both engines —is_executable_linefell back to agrep -Efork for every line it could not classify in pure Bash, and every tracked line is classified twice per run. 286 source lines cost 1055 grep forks.💡 Changes
caseglobs, removing the per-line fork.--coverageis 1.6x-2.3x faster (interleaved best-of-5: Bash 5.3 xtrace 3213→1396ms, Bash 3.2 trap 4655→2990ms)[^\)]also excludes\and[\{\}]also matches a bare line continuation--verbose, and warn when an explicitBASHUNIT_COVERAGE_ENGINE=xtracecannot be honoured instead of dropping it silently — the common case on macOS's Bash 3.2Verification
Both implementations run over the same 41173 lines across 395 files on Bash 3.2 and 5.3: zero disagreements. The differential harness was mutation-tested — deliberately breaking each rule produced 54 and 4 mismatches respectively, so it discriminates.
Coverage totals unchanged (
129/286trap,174/286xtrace) and still match between--paralleland sequential per engine. The two engines differing is documented expected behaviour, not a regression.Diff coverage from the issue is deliberately not in scope here; filed separately.