Source Code Management

Branching Model

The PX4 project uses a three-branch Git branching model:

• master (opens new window) is by default unstable and sees rapid development.
• beta (opens new window) has been thoroughly tested. It's intended for flight testers.
• stable (opens new window) points to the last release.

We try to retain a linear history through rebases (opens new window) and avoid the Github flow (opens new window). However, due to the global team and fast moving development we might resort to merges at times.

To contribute new functionality, sign up for Github (opens new window), then fork (opens new window) the repository, create a new branch (opens new window), add your changes, and finally send a pull request (opens new window). Changes will be merged when they pass our continuous integration (opens new window) tests.

All code contributions have to be under the permissive BSD 3-clause license (opens new window) and all code must not impose any further constraints on the use.

Code Style Formatting

PX4 uses astyle (opens new window) for code formatting. Valid versions are

• astyle 2.06 (opens new window) (deprecated)
• astyle 3.0 (opens new window)
• astyle 3.01 (opens new window) (recommended)

Once installed, formatting can be checked with ./Tools/astyle/check_code_style_all.sh. The output should be Format checks passed on a clean master. If that worked, make format can be used in the future to check and format all files automatically.

File name conventions

Going forward we aim to follow these file naming conventions:

• C++ source files should be named in CamelCase and match the class name. E.g. A C++ file containing a class named FooThing should be named FooThing.cpp.

• C++ header files should be named the same as source files except have the suffix .hpp.

• C++ header files that are required to be C compatible, should have the suffix .h.

• Folder names are snake_case for the first level inside modules/drivers/systemcmds/etc. but should be named CamelCase when more deeply nested to match the source and header files.

• Test files must have a Test suffix as shown: FooThingTest.cpp.

• One exception to the rules above are the MAVLink streams in src/modules/mavlink/streams (opens new window) which are ALL_UPPERCASE.hpp matching the MAVLink message name.

In-Source Documentation

PX4 developers are encouraged to create appropriate in-source documentation.

Note

Source-code documentation standards are not enforced, and the code is currently inconsistently documented. We'd like to do better!

Currently we have two types of source-based documentation:

• PRINT_MODULE_* methods are used for both module run time usage instructions and for the Modules & Commands Reference in this guide.
  • The API is documented in the source code here (opens new window).
  • Good examples of usage include the Application/Module Template and the files linked from the modules reference.

• We encourage other in-source documentation where it adds value/is not redundant.

  TIP

  Developers should name C++ entities (classes, functions, variables etc.) such that their purpose can be inferred - reducing the need for explicit documentation.

  • Do not add documentation that can trivially be assumed from C++ entity names.
  • Commonly you may want to add information about corner cases and error handling.
  • Doxgyen (opens new window) tags should be used if documentation is needed: @class, @file, @param, @return, @brief, @var, @see, @note. A good example of usage is src/modules/events/send_event.h (opens new window).

Commits and Commit Messages

Please use descriptive, multi-paragraph commit messages for all non-trivial changes. Structure them well so they make sense in the one-line summary but also provide full detail.

Component: Explain the change in one sentence. Fixes #1234
Prepend the software component to the start of the summary
line, either by the module name or a description of it.
(e.g. "mc_att_ctrl" or "multicopter attitude controller").
If the issue number is appended as <Fixes #1234>, Github
will automatically close the issue when the commit is
merged to the master branch.
The body of the message can contain several paragraphs.
Describe in detail what you changed. Link issues and flight
logs either related to this fix or to the testing results
of this commit.
Describe the change and why you changed it, avoid to
paraphrase the code change (Good: "Adds an additional
safety check for vehicles with low quality GPS reception".
Bad: "Add gps_reception_check() function").
Reported-by: Name <email@px4.io>

Use git commit -s to sign off on all of your commits. This will add signed-off-by: with your name and email as the last line.

This commit guide is based on best practices for the Linux Kernel and other projects maintained (opens new window) by Linus Torvalds.