# Repository Guidelines

## Project Structure & Module Organization

This is a small C library built with CMake. Core implementation lives in
`src/error.c`. The public header is generated at build time from
`include/akerror.tmpl.h` by `scripts/generrno.sh`, which also generates
`src/errno.c` under the build directory. CMake package and pkg-config templates
are in `cmake/` and `akerror.pc.in`. Tests are one-file C programs in `tests/`;
shared test helpers live beside them, such as `tests/err_capture.h`.

## Build, Test, and Development Commands

Use an out-of-tree build:

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

`cmake -S . -B build` configures the build and generates `akerror.h`.
`cmake --build build` compiles `libakerror` and test executables. `ctest`
runs the registered unit tests. To emit CI-style results, use:

```sh
ctest --test-dir build --output-on-failure --output-junit "$(pwd)/ctest-junit.xml"
```

Mutation testing is available through:

```sh
cmake --build build --target mutation
scripts/mutation_test.py --target src/error.c --threshold 65
```

Code coverage is available through:

```sh
cmake --build build --target coverage
scripts/coverage.py --threshold 90 --branch-threshold 50
```

`scripts/coverage.py` configures its own instrumented build tree (default
`build/coverage`, `-DAKERR_COVERAGE=ON`), runs the CTest suite there, and
reports gcov line/branch coverage per library source. Thresholds gate each
file as well as the total. Coverage measures `src/error.c` and the generated
`src/errno.c` only; the public header's macros expand at their call sites, so
mutation testing is what checks those.

## Coding Style & Naming Conventions

Use C99-compatible C and follow the surrounding style. Functions and types use
the `akerr_` prefix; macros and constants use `AKERR_` or all-caps macro names
such as `PREPARE_ERROR`. Keep generated-code changes in templates or generator
scripts, not in build outputs. Preserve concise comments for invariants,
macro constraints, and non-obvious error lifecycle behavior.

## Testing Guidelines

Add tests as `tests/err_<behavior>.c`. Register each new test in the
`AKERR_TESTS` list in `CMakeLists.txt`; tests that intentionally abort must
also be listed in `AKERR_WILL_FAIL_TESTS`. Prefer focused executable tests that
return zero on success and use existing helpers such as `AKERR_CHECK`. Run the
CTest suite before submitting changes, and run mutation testing and coverage
when changing core control-flow, reference counting, stack-trace, or handler
behavior.

## Commit & Pull Request Guidelines

Recent commits use short, imperative, sentence-case subjects, for example
`Fix refcount leak and stack-trace buffer overflow`. Keep commits focused and
describe the observable behavior changed. Pull requests should include a brief
summary, tests run, and any compatibility impact for public macros, generated
headers, installation paths, or CMake/pkg-config consumers.

## Agent-Specific Instructions

Do not overwrite uncommitted user changes. Avoid editing generated files in
`build/`; update `include/akerror.tmpl.h`, `src/error.c`, CMake files, tests,
or scripts instead.