libakstdlib/README.md

# README

![build badge](https://source.starfort.tech/andrew/libakstdlib/actions/workflows/ci.yaml/badge.svg?branch=main)

`libakstdlib` wraps C standard library functions so that they report failures
through [libakerror](https://source.starfort.tech/andrew/libakerror)'s
`ATTEMPT { ... } HANDLE { ... }` error contexts instead of through return codes
and `errno`. It also provides a few data structures built on the same
convention (a doubly-linked list and a binary tree).

Every entry point returns `akerr_ErrorContext *` and is marked `AKERR_NOIGNORE`.
See `TODO.md` for the current state of the library: what is covered by tests,
which corner cases are still open, and which libc functions are not yet wrapped.

## Building

```sh
git submodule update --init --recursive   # deps/libakerror
cmake -S . -B build
cmake --build build
cmake --install build
```

A top-level build compiles the vendored `deps/libakerror`. When `libakstdlib` is
consumed as a subproject, it uses whatever `akerror::akerror` target or installed
package the parent provides instead.

## Testing

There are four harnesses. The first three take seconds; the fourth takes about
half an hour.

### 1. The test suite

```sh
cmake -S . -B build
cmake --build build
ctest --test-dir build --output-on-failure
```

Tests live one per file in `tests/test_<name>.c` and share the helpers in
`tests/aksl_capture.h` — `AKSL_CHECK()` for plain assertions (unlike `assert()`
it survives `-DNDEBUG`), `AKSL_CHECK_STATUS(call, expected)` to run a wrapper and
assert on the status it returns, and an `AKSL_RUN()` driver that additionally
fails any test which leaks a slot from libakerror's error pool.

To add a test, drop `tests/test_mything.c` in place and add `mything` to
`AKSL_TESTS` in `CMakeLists.txt`.

**Reading the results.** `CMakeLists.txt` splits tests into three lists, and two
of them invert the meaning of "Passed":

| List | Meaning |
|---|---|
| `AKSL_TESTS` | Ordinary tests. Must exit 0. |
| `AKSL_WILL_FAIL_TESTS` | Expected to abort by design — an unhandled error reaching `FINISH_NORETURN`, or a deliberate contract violation. Marked `WILL_FAIL`, so a non-zero exit is a pass. |
| `AKSL_KNOWN_FAILING_TESTS` | Assert the *correct* behaviour of a confirmed defect (see `TODO.md` §2.1). Also marked `WILL_FAIL`. |

So `ctest` reporting all green does **not** mean the library is defect-free — it
means the known-good tests passed and the known-bad ones are still failing in the
documented way. When a defect is fixed, its test starts passing, CTest reports it
as failed with *unexpectedly passed*, and that is the cue to move it from
`AKSL_KNOWN_FAILING_TESTS` into `AKSL_TESTS`.

Every test is capped with a 30-second CTest `TIMEOUT`. The list and tree code is
full of loops whose termination hangs on a single condition, so a bug of that
shape hangs the suite rather than failing it.

### 2. Sanitizers

```sh
cmake -S . -B build-asan -DAKSL_SANITIZE=ON
cmake --build build-asan
ctest --test-dir build-asan --output-on-failure
```

Builds the library, the tests and the vendored libakerror with ASan + UBSan and
`-fno-sanitize-recover=all`. Several of the open items in `TODO.md` §2 only
misbehave under instrumentation — the uninitialised `%s` in `aksl_realpath`, the
unbounded `vsprintf` behind `aksl_sprintf`, the missing `va_end` in the `printf`
family — so new tests for those should be run this way.

### 3. Code coverage

```sh
cmake -S . -B build-coverage -DAKSL_COVERAGE=ON
cmake --build build-coverage --target coverage
```

`-DAKSL_COVERAGE=ON` compiles the library and the tests with `--coverage -O0`,
and wires the report into the suite itself, so a plain
`ctest --test-dir build-coverage` also produces it. Two extra CTest entries
appear, held in place by a CTest fixture rather than by declaration order, so
they work under `ctest -j` too:

| Test | When | Does |
|---|---|---|
| `coverage_reset` | before every other test | deletes the accumulated `.gcda` counters |
| `coverage_report` | after every other test | aggregates `gcov` output, prints the summary, applies the threshold gate |

The reset matters: gcov counters are cumulative, so without it each report would
fold in every earlier run and overstate coverage.

CTest hides the output of a passing test, so `coverage_report` also writes
`build-coverage/coverage-summary.txt` (the same text report) and
`build-coverage/coverage.xml` (Cobertura, for CI publishers). The `coverage`
target above prints the report to the terminal for you; otherwise read the file
or use `ctest --test-dir build-coverage -V -R coverage_report`.

The report lists per-file line, branch and function coverage, then every
uncovered line and every function the suite never called — that listing is the
actionable part, the same way surviving mutants are for the harness below.

Drive the script directly for anything narrower:

```sh
scripts/coverage.py --build build-coverage                     # report on disk counters
scripts/coverage.py --build build-coverage --summary-only       # totals only
scripts/coverage.py --build build-coverage --include tests      # coverage of the tests themselves
scripts/coverage.py --build build-coverage --run-tests          # reset, run ctest, report
scripts/coverage.py --build build-coverage --threshold 50 --branch-threshold 25
```

It needs nothing but Python 3 and gcc's own `gcov` — no lcov, gcovr or genhtml.

To gate on coverage, set the threshold at configure time; `coverage_report` then
fails below it, and the same regression-ratchet logic applies as for the mutation
score:

```sh
cmake -S . -B build-coverage -DAKSL_COVERAGE=ON \
      -DAKSL_COVERAGE_THRESHOLD=50 -DAKSL_COVERAGE_BRANCH_THRESHOLD=20
```

Two caveats. Coverage is measured at `-O0`, because the optimizer reorders lines
until per-line counts stop matching the source — so a coverage build is not the
build to profile. And gcov flushes its counters at normal process exit, which an
`AKSL_WILL_FAIL_TESTS` entry that aborts by design never reaches: such a test
contributes no coverage data at all, so lines only it reaches are reported as
uncovered.

### 4. Mutation testing

The suite tells you the library works. Mutation testing tells you the *suite*
works: it breaks the library in small ways, one at a time, and checks that the
tests notice.

```sh
cmake --build build --target mutation        # src/stdlib.c + include/akstdlib.h
```

or drive the script directly for a faster or narrower run:

```sh
scripts/mutation_test.py --target src/stdlib.c            # C source only
scripts/mutation_test.py --target src/stdlib.c --list     # enumerate, build nothing
scripts/mutation_test.py --target src/stdlib.c --max-mutants 20
scripts/mutation_test.py --target src/stdlib.c --threshold 40
```

A mutant that makes the tests fail is *killed* (good); one the tests still pass
is a *survivor*, and names a missing test. The score is `killed / total`, and the
run prints every survivor with `file:line` and the exact edit. The harness never
touches your working tree — it copies the repo to a scratch directory and mutates
the copy.

CI runs the `src/stdlib.c` set with `--threshold 40`. That is a regression
ratchet rather than a quality bar: the current score is 46.8%, and the survivors
are concentrated in the wrappers that have no tests yet. Raise the threshold as
coverage lands.

## The pre-push hook

`.githooks/pre-push` runs the fast harnesses — the default build and the
sanitizer build, each followed by `ctest` — before letting a push out. Enable it
once per clone:

```sh
git config core.hooksPath .githooks
```

It only builds when there are commits to push (a branch deletion is a no-op), and
it builds under `.git/aksl-prepush` so it never disturbs your own `build/`.

```sh
AKSL_HOOK_MUTATION=1 git push    # also run the mutation gate (slow)
git push --no-verify             # skip the hook entirely
```

Other knobs: `AKSL_MUTATION_THRESHOLD` (default 40, keep it in step with
`.gitea/workflows/ci.yaml`) and `AKSL_HOOK_BUILD_DIR`.