libakstdlib/README.md

README

libakstdlib wraps C standard library functions so that they report failures through 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

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

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

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

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:

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:

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.

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

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

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:

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/.

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.