Contributing to libc++

Please read this document on general rules to contribute to LLVM projects.

Tasks and processes

This file contains notes about various tasks and processes specific to libc++.

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, 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!

Post-Release TODO

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

Modifying feature test macros

When adding or updating feature test macros, you should update the corresponding tests. To do that, modify feature_test_macros table in the script utils/generate_feature_test_macro_components.py, run it, and commit updated files.

Adding a new header TODO

When adding a new header to libc++:

  1. Add a test under test/libcxx that the new header defines _LIBCPP_VERSION. See test/libcxx/algorithms/version.pass.cpp for an example.
  2. Run python utils/generate_header_tests.py, verify and commit the modifications.
  3. Create a submodule in include/module.modulemap for the new header.
  4. Update the include/CMakeLists.txt file to include the new header.

Exporting new symbols from the library

When exporting new symbols from libc++, one 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.