libakerror/TODO.md

# TODO

Working notes for `libakerror`. Outstanding items only.

## 1. Only ThreadSanitizer is wired into CI, not ASan/UBSan

`AKERR_SANITIZE` builds the library and the tests with any sanitizer list, and
CI runs `-DAKERR_SANITIZE=thread` through `scripts/thread_test.sh`. Nothing runs
`address,undefined` yet, and that is the one that covers the original
motivation: mutation testing caught an out-of-bounds probe in the status-name
hash table that the suite could not, because the failure mode was a write into
adjacent BSS, which does not crash. Sharpening one test closed that instance;
ASan would catch the whole class regardless of how sharp the assertions are.

The machinery is in place — this is one more job in
`.gitea/workflows/ci.yaml` running
`cmake -S . -B build/asan -DAKERR_SANITIZE=address,undefined`. Left separate
because ASan and TSan cannot be combined in one build.

## 2. `HANDLE`-level status aliasing is still undetectable

Two components can compile the same integer into a `case` label without ever
reserving a range or registering a name, and nothing sees it. Ownership
enforcement covers *naming*, which is the part the library mediates; the `case`
label never reaches it.

Closing this needs the `if`/`else if` handler ladder — rewriting
`PROCESS`/`HANDLE`/`HANDLE_GROUP`/`HANDLE_DEFAULT`/`FINISH` so status matching
is not restricted to integer constant expressions. That would also allow
matching on ranges or predicates, and would let a handler resolve a code through
its owner. It touches the most load-bearing code in the library and every
consumer's error handling at once, so it wants its own change.

Note it would *not* by itself fix the "don't use `CATCH` or `FAIL_*_BREAK`
inside a loop" hazard: that comes from exiting via `break`, not from `switch`.

## 3. No registry introspection

There is no way to ask who owns a status, or to enumerate reservations. The
"coordinate ranges at the dependency-stack level" advice in UPGRADING.md
therefore has no tooling behind it.

A read-only accessor plus a dump through `akerr_log_method` would let a startup
self-check or a CI job print the whole map for a linked stack. Cheap, additive,
and the natural next step for multi-component adoption.

## 4. No way to release a reservation

A plugin host that `dlopen`s many distinct plugins over a process lifetime
accumulates ranges until the table fills. Reloading the *same* plugin is fine —
an identical repeat by the same owner is idempotent.

## 5. Renaming a status is not safe against a concurrent lookup

`akerr_name_for_status(status, NULL)` returns a pointer into the registry rather
than a copy, which is what makes it usable from inside `FAIL` — it needs no
buffer and no error context of its own. Registering a *second* name for a status
that already has one (`tests/err_name_ownership.c` covers that it is allowed)
overwrites that buffer in place, so a thread reading the name at that moment can
see a torn string. Every other registry operation is serialized; this one cannot
be, because the reader is outside the lock by the time it reads the characters.

Documented in docs/thread-safety.md and UPGRADING.md as "register names during
initialization". Closing it properly means making a registered name immutable —
either refusing a rename outright (a behavior change, and
`tests/err_name_ownership.c` asserts the current contract), or copying names
into a bump-allocated arena and publishing the pointer with a release store, so
a rename allocates new storage instead of rewriting live storage. The arena is
the better answer; it costs a second capacity limit and its exhaustion path.

## 6. Deprecate the two-argument name-registration path

`akerr_name_for_status(status, name)` cannot identify its caller, so it can only
check that *some* reservation covers the status, not that the caller owns it. It
exists for migration. Once consumers have moved to
`akerr_register_status_name()`, make the set path a no-op or remove it and leave
`akerr_name_for_status()` as pure lookup.

## 7. `akerr_init()`'s own reservation failure is untested

`tests/err_library_status_fatal.c` covers the terminal path in
`__akerr_name_library_status()` by naming a status the library does not own. The
band reservation in `akerr_init()` has no such handle: it can only fail in a
build whose tables are too small for the library's own entries, and both sizes
are `PRIVATE` to the library target, so a test executable cannot set them.

Closing it means a second library target built with tiny tables plus a
`WILL_FAIL` test linked against it. Nothing in the CMake does that yet: the
sanitizer and coverage options vary the *flags* of the one library target, not
its compile definitions.

Related: branch coverage on `src/error.c` now sits just above its 50% gate.
Every `FAIL_*` site carries about six branch outcomes of error-construction
machinery (`ENSURE_ERROR_READY`, `AKERR_STACKTRACE_APPEND`) that only run when
that specific failure fires, and every `PASS` site around a call that cannot
fail carries about twenty-five. Validating more inputs therefore lowers the
ratio by construction. Before adding defensive checks, expect to add a test that
drives them, as `tests/err_copy_string.c` does.

## 8. Mutation testing judges concurrency mutants without a sanitizer

`scripts/mutation_test.py` configures each mutant build with the default CMake
options, so a mutant that only breaks under concurrency is judged by a suite
running without ThreadSanitizer. Deleting the pool's `akerr_mutex_lock()` call
survives the run even though it is a real race: rebuilt and run directly, that
mutant fails `tests/err_threads_pool.c` in 4 of 10 runs, and fails under
`scripts/thread_test.sh` in 5 of 5. So 81.2% is a floor for that category, not a
verdict.

Closing it means a `--cmake-arg` passthrough on the harness so the mutant build
can be configured with `-DAKERR_SANITIZE=thread`. The whole run then costs a
TSan-instrumented suite per mutant (roughly 6s instead of 0.4s), so it belongs
behind a flag rather than in the default target or in CI.

## 9. No way to keep an error context and report it at the same time

A context can be handed to another thread and released there --
`docs/thread-safety.md` now documents that pattern and
`tests/err_threads_handoff.c` proves it -- but it is a *move*. A thread that
wants to both keep its error and report it upward has to read the fields out
into its own record, and it loses the stack trace doing so, because
`stacktracebuf` is the one thing that cannot be usefully summarized.

Copying the struct is not a workaround. `stacktracebufptr` is self-referential
(`include/akerror.tmpl.h`), so `akerr_ErrorContext c = *src;` leaves the copy's
cursor pointing into the source's buffer -- the copy logs correctly and then
corrupts a slot it does not own the first time anything appends to it. `arrayid`
is restored after the wipe in `akerr_release_error()` (`src/error.c:395-398`), so
a copied id makes the destination impersonate the source's slot for the life of
the process.

If this is ever worth an API, the shape is:

```c
akerr_ErrorContext AKERR_NOIGNORE *akerr_copy_error(akerr_ErrorContext *source,
						    akerr_ErrorContext *destination);
```

taking the destination as a parameter rather than allocating it. An allocating
copy could fail on pool exhaustion, and reporting *that* failure needs a pool
slot, so it would have to abort -- adding a third `exit()` site to a library that
deliberately has two. Caller-allocates puts the pool pressure where it can be
managed. The copy must repair four fields: `arrayid` (the destination's own),
`refcount` (set to 1, never inherited), `handled` (false -- a copy is a fresh
obligation, or `FINISH_NORETURN` on the receiving side drops it silently), and
`stacktracebufptr` (re-anchored to the destination's buffer at the *same offset*,
so a later append continues the trace instead of overwriting it).

Not worth building yet: no consumer needs it. The trigger is a consumer that
needs a worker's stack *trace*, not just its status and message, at the join
point -- `libakstdlib`'s planned `pthread_*` wrappers are the likely first.

## Unrelated pre-existing issues

- The `AKERR_USE_STDLIB=OFF` build does not compile at all: `bool`, `PATH_MAX`
  and `NULL` are used unconditionally but only included under the stdlib branch.
  `docs/building.md`'s dependency list states what a replacement must provide,
  but the header still needs its includes untangled for that configuration to
  work.
- `CMakeLists.txt` sets `main_lib_dest` from `MY_LIBRARY_VERSION`, which is never
  defined and never read. Dead line.