How to Contribute

Contributions are always welcome! And there is a multitude of ways in which you can help depending on what you like to do, or are good at. Anything from documentation, code cleanup, issue completion, new features, you name it, even filing issues is contributing and greatly appreciated!

Another really great way to help is if you find an interesting, or helpful way in which to use clap. You can either add it to the examples/ directory, or file an issue and tell me. I'm all about giving credit where credit is due :)

Testing Code

To test with all features both enabled and disabled, you can run these commands:

$ cargo test --no-default-features
$ cargo test --features "yaml unstable"

Alternatively, if you have just installed you can run the prebuilt recipes. Not using just is perfectly fine as well, it simply bundles commands automatically.

For example, to test the code, as above simply run:

$ just run-tests

From here on, I will list the appropriate cargo command as well as the just command.

Sometimes it's helpful to only run a subset of the tests, which can be done via:

$ cargo test --test <test_name>

# Or

$ just run-test <test_name>

Linting Code

During the CI process clap runs against many different lints using clippy. In order to check if these lints pass on your own computer prior to submitting a PR you'll need a nightly compiler.

In order to check the code for lints run either:

$ rustup override add nightly
$ cargo build --features lints
$ rustup override remove

# Or

$ just lint

Debugging Code

Another helpful technique is to see the clap debug output while developing features. In order to see the debug output while running the full test suite or individual tests, run:

$ cargo test --features debug

# Or for individual tests
$ cargo test --test <test_name> --features debug

# The corresponding just command for individual debugging tests is:
$ just debug <test_name>

Commit Messages

I use a conventional changelog format so I can update my changelog automatically using clog

  • Please format your commit subject line using the following format: TYPE(COMPONENT): MESSAGE where TYPE is one of the following:
    • api - An addition to the API
    • setting - A new AppSettings variant
    • feat - A new feature of an existing API
    • imp - An improvement to an existing feature/API
    • perf - A performance improvement
    • docs - Changes to documentation only
    • tests - Changes to the testing framework or tests only
    • fix - A bug fix
    • refactor - Code functionality doesn't change, but underlying structure may
    • style - Stylistic changes only, no functionality changes
    • wip - A work in progress commit (Should typically be git rebase'ed away)
    • chore - Catch all or things that have to do with the build system, etc
    • examples - Changes to existing example, or a new example
  • The COMPONENT is optional, and may be a single file, directory, or logical component. Parenthesis can be omitted if you are opting not to use the COMPONENT.

Tests and Documentation

  1. Create tests for your changes
  2. Ensure the tests are passing. Run the tests (cargo test --features "yaml unstable"), alternatively just run-tests if you have just installed.
  3. Optional Run the lints (cargo build --features lints) (requires a nightly compiler), alternatively just lint
  4. Ensure your changes contain documentation if adding new APIs or features.

Preparing the PR

  1. git rebase into concise commits and remove --fixups or wip commits (git rebase -i HEAD~NUM where NUM is number of commits back to start the rebase)
  2. Push your changes back to your fork (git push origin $your-branch)
  3. Create a pull request against master! (You can also create the pull request first, and we'll merge when ready. This a good way to discuss proposed changes.)

Other ways to contribute

Another really great way to help is if you find an interesting, or helpful way in which to use clap. You can either add it to the examples/ directory, or file an issue and tell me. I'm all about giving credit where credit is due :)


There are a few goals of clap that I‘d like to maintain throughout contributions. If your proposed changes break, or go against any of these goals we’ll discuss the changes further before merging (but will not be ignored, all contributes are welcome!). These are by no means hard-and-fast rules, as I'm no expert and break them myself from time to time (even if by mistake or ignorance :P).

  • Remain backwards compatible when possible
    • If backwards compatibility must be broken, use deprecation warnings if at all possible before removing legacy code
    • This does not apply for security concerns
  • Parse arguments quickly
    • Parsing of arguments shouldn't slow down usage of the main program
    • This is also true of generating help and usage information (although slightly less stringent, as the program is about to exit)
  • Try to be cognizant of memory usage
    • Once parsing is complete, the memory footprint of clap should be low since the main program is the star of the show
  • panic! on developer error, exit gracefully on end-user error