9874ce6 May 6, 2017
@technomancy @hyPiRion @hugoduncan
114 lines (89 sloc) 4.94 KB


Leiningen is the most widely-contributed-to Clojure project. We welcome potential contributors and do our best to try to make it easy to help out. Contributors who have had a single patch accepted may request commit rights as well as two free stickers.

Discussion occurs both in the #leiningen channel on Freenode and on the mailing list. To join the mailing list, email with subscribe in the Subject field, then follow the instructions in the reply you receive. The address is used for posting once you've joined.

Please report issues on the GitHub issue tracker or the mailing list. Sending bug reports to personal email addresses is inappropriate. Simpler issues appropriate for first-time contributors looking to help out are tagged "newbie".

Patches are preferred as patches from git format-patch on the mailing list or as GitHub pull requests. Please use topic branches when sending pull requests rather than committing directly to master in order to minimize unnecessary merge commit clutter. Direct pull requests towards the master branch, not the stable branch.

Leiningen is mirrored at GitLab and tested on CircleCI.


The definitions of the various tasks reside in src/leiningen in the top-level project. The underlying mechanisms for things like project.clj parsing, classpath calculation, and subprocess launching are implemented inside the leiningen-core subproject.

See the readme for the leiningen-core library and doc/ for more details on how Leiningen's codebase is structured.

Try to be aware of the conventions in the existing code, except the one where we don't write tests. Make a reasonable attempt to avoid lines longer than 80 columns or function bodies longer than 20 lines. Don't use when unless it's for side-effects. Don't introduce new protocols. Use ^:internal metadata to mark vars which can't be private but shouldn't be considered part of the public API.


You don't need to "build" Leiningen per se, but when you're developing on a checkout you will need to get its dependencies in place and compile some of the tasks. Assuming you are in Leiningen's project root, you can do that like this:

$ cd leiningen-core
$ lein bootstrap # or lein.bat on Windows.

The lein command is a stable release of Leiningen on your $PATH – preferably the newest one. If you don't have a stable lein installed, simply check out the stable branch and copy bin/lein to somewhere on your $PATH, then switch your branch back.

If you want to use your development copy for everyday usage, symlink bin/lein to somewhere on your $PATH. You'll want to rename your stable installation to keep them from interfering; typically you can name that lein2 or lein-stable.

When dependencies in Leiningen change, you may have to do rm .lein-classpath in the project root, though in most cases this will be done automatically. If dependencies in leiningen-core change, you have to redo the lein bootstrap step mentioned earlier.

Using bin/lein alone from the master branch without a full checkout is not supported. If you want to just grab a shell script to work with, use the stable branch.

Uberjar from Master

Since a development version is not uberjared, it can be rather slow compared to a stable release. If this is annoying and you depend on a recent fix or enhancement, you can build an uberjar from master as follows:

# NB! You have to use *bin*/lein to build the uberjar
$ bin/lein uberjar
# ^ Last line printed from this command will tell the location of the standalone
$ cp target/leiningen-2.5.2-SNAPSHOT-standalone.jar $HOME/.lein/self-installs
$ cp bin/lein $HOME/bin/lein-master

Here, 2.5.2-SNAPSHOT is the version we've built, and we have $HOME/bin on our $PATH.

Note that changes on master won't be visible in the uberjared version unless you overwrite both the lein script and a freshly created uberjar.


Before you're asking for a pull request, we would be very happy if you ensure that the changes you've done doesn't break any of the existing test cases. While there is a test suite, it's not terribly thorough, so don't put too much trust in it. Patches which add test coverage for the functionality they change are especially welcome.

To run the test cases, run bin/lein test in the root directory: This will test both leiningen-core and leiningen itself. Do not attempt to run the tests with a stable version of Leiningen, as the namespaces conflict and you may end up with errors during the test run.