Source code formatting

C++ formatting: clang-format

Code formatting is handled by clang-format. A configuration file is available in the repository root at .clang-format and should be used to automatically format the code. Many editors / IDEs support clang-format and also format-on-save actions.

The ACTS CI system will automatically check code formatting using the provided clang-format configuration and will notify incompatible formatting.

To simplify this, a script located in CI/check_format can be used like:

$ CI/check_format $SOURCE_DIR

In some cases, different clang-format versions will result in slightly different outputs. In many cases, this is accepted by the CI. However, it is recommended to use the same major version of clang-format to perform local formatting. If you are comfortable with Docker, you can use the docker image used by the CI. You can use the script located in CI/check_format_local similar to the description above. Other options to obtain a compatible clang-format version are to use your package manager (e.g. Ubuntu distributions usually offer a set of versions to install), or to use statically linked binaries from here1.

You can also download the required changes by clicking on Summary on the top left-hand portion of the CI job and scrolling down to the bottom of the page (see Changed). However, it is suggested to run the CI/check_format locally before committing, to not clog the shared resources with repeated checks.

Python formatting

Formatting of the Python source code uses the library black. To run it, you can locally install the black package. You can use pip to install it:

$ pip install black
$ black <source> 


It is strongly recommended to use a virtual environment for this purpose! For example, run

$ python -m venv venv
$ source venv/bin/activate

and then install and use black. You can also use a tool like pipx to simplify this.


This repository is external to the ACTS project, so proceed with caution!