testsAndMisc/docs/shell-split-verification.md

Shell split verification: how a green split is still broken

Split out of docs/shell-split-recipes.md when that file hit the same 250-line cap it exists to serve. That file covers how to make a split; this one covers how to find out it is wrong. Read both before the next linux_configuration or phone_focus_mode split.

Every section below cost a failed run, a revert, or — once — a live system mutation.

A --skip-install flag is not evidence the script is safe to run

shell_check.sh gates only install_if_missing's pacman branch on SKIP_INSTALL. The AUR branch inside install_linters runs regardless, so a backgrounded "baseline" run installed four packages (python-pbr, python-fixtures, python-discover, python-reno) before it was killed mid-makepkg. Decision 6 was violated by a flag that looked like it granted permission.

Before running any script to capture a baseline, grep the flag's variable and confirm it gates every mutation path, not just the first one:

grep -n 'SKIP_INSTALL\|DRY_RUN' <script>   # then read each hit

--list-only was the genuinely safe path here, because it returns before install_linters is reached at all.

A stubbed run cannot reach a bug in a seam that passes state

meta/scripts/verify_shell_split.sh and the hand-rolled declare -F probe both source the libs and never call the functions. That is enough to prove every source line resolves, and nothing more. The analyze_repo.sh split passed bash -n, shellcheck, a function-set diff, a line-set diff and the stubbed probe — and still shipped a script that aborted immediately after language detection. Two separate bugs, neither reachable without executing:

• set -e and the function tail. Eight ((LANG_FILES[x] > 0)) && HAS_Y=true lines were top-level statements, where a false && merely leaves $? non-zero. Wrapped into a function they become its return value, and the last one (java, false for most repos) killed the script. Any time you wrap former top-level code in a function, check what its last statement is; append || true if it is a bare conditional.
• A self-referencing nameref. local -n LANG_CODE_FILES="$1" pointing at a global of the same name still moves data on bash 5.3, but warns circular name reference on every access — straight into the script's output. Name the local something else (_code_files).

So: when a seam passes state, run the thing. Stub only the parts that mutate the system, and diff the generated artifacts against a detached worktree at the pre-split commit. That comparison is what proved the fix — same file set, every text artifact byte-identical.

Note the knock-on: renaming the nameref local hides the array from shellcheck (SC2034), because it is then only ever named as a bare word. Pass the name through a variable (CODE_FILES_MAP="LANG_CODE_FILES") so the reference is real, rather than suppressing.

Do not make a clean file shfmt-dirty

157 of 298 linux_configuration shell files already fail shfmt and there is no .editorconfig or shfmt pre-commit hook, so shell_check.sh's run_linters exits 1 on the full tree regardless. That is not licence to add more: check shfmt -d <file> before and after a split. analyze_repo.sh was clean and a split made it dirty over one double blank line.

shfmt -w also deletes comment banners it considers stray — it removed a #==== STEP header. Re-count the banners after running it.