.. _ContributingToLibcxx:

======================
Contributing to libc++
======================

This file contains notes about various tasks and processes specific to contributing
to libc++. If this is your first time contributing, please also read `this document
<https://www.llvm.org/docs/Contributing.html>`__ on general rules for contributing to LLVM.

For libc++, please make sure you follow `these instructions <https://www.llvm.org/docs/Phabricator.html#requesting-a-review-via-the-command-line>`_
for submitting a code review from the command-line using ``arc``, since we have some
automation (e.g. CI) that depends on the review being submitted that way.

Looking for pre-existing reviews
================================

Before you start working on any feature, please take a look at the open reviews
to avoid duplicating someone else's work. You can do that by going to the website
where code reviews are held, `Differential <https://reviews.llvm.org/differential>`__,
and clicking on ``Libc++ Open Reviews`` in the sidebar to the left. If you see
that your feature is already being worked on, please consider chiming in instead
of duplicating work!

Pre-commit check list
=====================

Before committing or creating a review, please go through this check-list to make
sure you don't forget anything:

- Do you have tests for every public class and/or function you're adding or modifying?
- Did you update the synopsis of the relevant headers?
- Did you update the relevant files to track implementation status (in ``docs/Status/``)?
- Did you mark all functions and type declarations with the :ref:`proper visibility macro <visibility-macros>`?
- If you added a header:

  - Did you add it to ``include/module.modulemap``?
  - Did you add it to ``include/CMakeLists.txt``?
  - If it's a public header, did you add a test under ``test/libcxx`` that the new header defines ``_LIBCPP_VERSION``? See ``test/libcxx/algorithms/version.pass.cpp`` for an example. NOTE: This should be automated.
  - If it's a public header, did you update ``utils/generate_header_inclusion_tests.py``?

- Did you add the relevant feature test macro(s) for your feature? Did you update the ``generate_feature_test_macro_components.py`` script with it?
- Did you run the ``libcxx-generate-files`` target and verify its output?

Post-release check list
=======================

After branching for an LLVM release:

1. Update ``_LIBCPP_VERSION`` in ``include/__config``
2. Update the ``include/__libcpp_version`` file
3. Update the version number in ``docs/conf.py``

Exporting new symbols from the library
======================================

When exporting new symbols from libc++, you must update the ABI lists located in ``lib/abi``.
To test whether the lists are up-to-date, please run the target ``check-cxx-abilist``.
To regenerate the lists, use the target ``generate-cxx-abilist``.
The ABI lists must be updated for all supported platforms; currently Linux and
Apple.  If you don't have access to one of these platforms, you can download an
updated list from the failed build at
`Buildkite <https://buildkite.com/llvm-project/libcxx-ci>`__.
Look for the failed build and select the ``artifacts`` tab. There, download the
abilist for the platform, e.g.:

* C++20 for the Linux platform.
* MacOS C++20 for the Apple platform.