The instrument, not the tests, was the bottleneck. Coverage is now
(PS4-traced lines | kcov hits) & (kcov line set - continuation lines).
The trace deliberately does NOT supply the denominator. A trace reports only
lines that RAN, so using it for both halves would make every subject 100.00%
and arm a repo-wide gate that checks nothing.
Three measured findings, each of which yields a silently wrong trace:
1. kcov's ptrace and bash's xtrace cannot share a process. Under
SHELLOPTS=xtrace every line kcov recorded as hits="1" comes back hits="0"
-- reproduced A/B on one subject. Hence two passes, two namespaces.
2. SHELLOPTS is readonly inside bash, so `export SHELLOPTS=xtrace` fails and
tracing never turns on; and `set -x` does not reach child processes.
3. Decisive: bash under `unshare --map-root-user` runs PRIVILEGED and
DISCARDS an inherited PS4, falling back to "+ " while still honouring
xtrace. The trace loses its file:line prefix and every subject reads 0%.
Fixed by delivering PS4 and `set -x` through a BASH_ENV file, which also
solves child-process propagation.
A fourth trap, in the report: kcov records filename="dwm_config.sh", a bare
basename. The source path comes from the trace's ${BASH_SOURCE} or a unique
repo search; an ambiguous basename yields no exclusion rather than a guess.
Measured through run_all.sh, nothing down:
dot_resolver_install.sh 39/39 = 100.00% (acceptance, unchanged)
rpi_nc_ca.sh 73/73 = 100.00% (was 72/73 = 98.63%)
dwm_config.sh 65/66 = 98.48% (was 35/73 = 47.95%)
rpi_nc_install.sh 85/88 = 96.59% (was 10/88 = 11.36%)
rpi_nc_ca reaching 100% is the load-bearing check: its missing line 141 was
cross-process contagion, and the trace pass has no kcov in it to contaminate.
dwm_config's remaining line 39 is a `done < <(...)`. Left in the denominator
on purpose -- removing lines inflates coverage, the fail-open direction, so a
second exclusion rule needs per-line justification, not a pattern from one lib.
Both new Python modules hold 100% branch coverage (29 tests).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
nc_php.sh was the next-hardest library on the allowlist. It targets a
Debian Raspberry Pi -- it edits /etc/php/<ver>/apache2/php.ini, drives
occ as www-data and installs a crontab -- so none of its write targets
exist on this Arch host and the jail had nothing to mirror.
- --seed-dir / --seed-file create the paths a foreign-platform subject
expects. Verified with a probe: /etc/php/8.2/apache2 exists inside
the jail while /etc/php does not exist outside it.
- A failed bind is now FATAL, and missing mountpoints are created
first. A bind that fails silently is indistinguishable from
unreachable code in the report, which is the misdiagnosis this
runner exists to prevent.
- Mirroring skips unreadable targets (/root as a normal user) rather
than aborting under set -e.
nc_php.sh: 84/85 = 98.82%, 24 assertions. It STAYS on the allowlist,
because 98.82% is below the bar. Line 111 -- the crontab first-run
fallback -- hung the suite on both attempts to cover it, so it is left
uncovered and documented rather than tried a third time.
Two harness hazards found the hard way and written down: a top-level
stub function shadows the subject's own function for every later
assertion (this silently dropped coverage 83.53% -> 57.65% while the
tests still passed), and a stub for a piped-into command must drain
stdin or the writer takes SIGPIPE.
dot_resolver_install.sh still measures 39/39 = 100.00%.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DbD4nco3EgL1UFoZKmKsLE
The gate was a presence check -- 'a run_all.sh exists beside this lib' --
which an empty suite that asserts nothing satisfies. It now measures.
100% is reachable with no suppressions and no production source changes:
run the suite inside a user+mount namespace and the sudo-writes, systemd
units and nftables rules execute for real against a throwaway /etc.
- meta/scripts/shell_coverage_jail.sh: the runner, promoted out of a
session scratchpad. Two fixes it needed on the way: bind targets mirror
the real directory tree (an empty bind makes writes fail with ENOENT,
which reads as unreachable code), and sudo gets a pass-through stub
because real sudo cannot setresuid inside a userns.
- It fingerprints git status before and after and fails the run if a
write escapes the jail. Verified with a deliberate escapee.
- dot_resolver_install.sh: 39/39 = 100.00%, 28 assertions. Picked by
scoring every allowlisted lib on root ops, system writes and
destructive calls -- it scored highest in the repo. Allowlist 106 -> 105.
- jscpd was already over its own threshold at 2.45% and would have
rejected every commit staging a .sh file. Excluding vendored .venv/
shell alone gives 1.67%; also excluding lib/tests/ gives 1.47%.
The gate is deliberately NOT wired into the hook chain yet.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DbD4nco3EgL1UFoZKmKsLE
