Ecosystem: Library Development and Distribution

  1. Prequisites
  2. Publishing Libraries
    1. Publishing to GitHub
    2. Publishing to Clojars
  3. Creating New Projects
    1. Installing deps-new
    2. Create the Project with deps-new
    3. A Note Regarding Project Naming
  4. Making the Project your own
    1. Licensing
    2. Update the README
  5. Create your project's local git repository
  6. Write Tests
  7. Write Code
  8. Run Tests
  9. Commit any remaining changes
  10. Complete the GitHub Project Setup and Upload your Code
    1. Making a Release on GitHub
  11. Upload to Clojars
  12. Generate API docs (optional)
  13. Announce (optional)
  14. Make Updates to your library
    1. Merging pull-requests
  15. See Also
  16. Contributors

This guide covers how to create your own typical pure Clojure library and distribute it to the community via Clojars, as well as making it available in source form on a public repository such as GitHub.

Prequisites

This guide assumes you have an account on a public hosting service like GitHub and you will need to use your account name as part of your project. In this guide, we use clojure-example-library as the account name: you should substitute your own account name wherever you see clojure-example-library in this guide! We will use my-cool-lib as the name of the new project we create and publish here, but you can use whatever name you want -- just remember to substitute that wherever you see my-cool-lib in this guide.

This guide uses Clojure 1.11 and a recent version of the Clojure CLI (at least 1.11.1.1139; current version is 1.11.4.1474 as of August 2024), and requires you have git installed (though very little familiarity with git is required).

Note: you should always ensure you have an up-to-date version of the Clojure CLI installed! See Tools Releases. Several of the examples here require 1.11.1.1139 or later: clojure -version should tell you the version you have installed.

It's assumed that you're already somewhat familiar with Clojure. If not, see the Getting Started and Introduction guides.

This work is licensed under a Creative Commons Attribution 3.0 Unported License (including images & stylesheets). The source is available on Github.

Note: If you're using Leiningen, read the Library Development and Distribution with Leiningen guide.

Publishing Libraries

Prior to the appearance of the Clojure CLI in 2018, it was generally assumed that you would publish the source of your library to a public service like GitHub, but that you would also need to package your library as a JAR file and deploy it to Clojars (or Maven Central) so that it was available for others to use in their projects as a dependency.

The Clojure CLI can treat projects hosted on public services, like GitHub, as first-class dependencies, so that it is no longer necessary to package and deploy your library elsewhere -- if you expect your users to consume the library directly in source form. In order to make your library available to users who are working with Leiningen (or other build tools), it is still required to package and deploy your project as a JAR file -- which this guide also covers.

Publishing to GitHub

If you don't already have a GitHub account, create one, then log into it. GitHub provides good documentation on how to get started and how to create an SSH key pair. If you haven't already done so, get that set up before continuing.

Go to the Repositories tab and create a new repository there for your project using the icon/button/link (near the top-right if you already have existing projects, else prominently in the middle if this is your first repository).

You will have your local repository, and also a remote duplicate of it at GitHub.

For the repository name, we'll use my-cool-lib in this guide (but you can use whatever name you want). Provide a one-line description if you want, make sure to select Public so that others can access your project, and hit "Create repository".

You do not need GitHub to provide a README, a .gitignore file, or a license, since we'll add those.

For a project published to GitHub as clojure-example-library/my-cool-lib, the default dependency for others to use would be:

  io.github.clojure-example-library/my-cool-lib {:git/sha "..."}

Where the "..." value would be the full SHA (hex string) for the version that they wanted to use (e.g., from the latest commit).

If you have tagged a release on GitHub, e.g., v0.1.0 then you can use :git/tag "v0.1.0" and the :git/sha value can be the "short SHA" -- just the first seven characters of the hex string.

The Clojure CLI understands that io.github.<account>/<repo> maps to https://github.com/<account>/<repo> in order to fetch the repository. The CLI understands several source code repositories so you could use GitLab, BitBucket, Beanstalk, or Sourcehut (as of May 2023).

Publishing to Clojars

If you don't already have an account, you will need to register on Clojars. It will convenient for you to use the same email account as you use for GitHub, so that you can login to Clojars in future via GitHub, which will automatically verify your GitHub-associated "group ID" with Clojars (e.g., io.github.<account>). See Verified Group Names for more details.

You will also need to set up at least one deploy token and provide environment variables when you get to the point of actually deploying your library JAR to Clojars:

  • CLOJARS_USERNAME -- set to your Clojars username
  • CLOJARS_PASSWORD -- set to a valid deploy token

If you don't want to connect your Clojars account to your GitHub account, you can use net.clojars.<username> as your "group ID" for deploying projects. That style of group name is always verified for Clojars.

Creating New Projects

If you only ever intend to publish your library to GitHub and not to Clojars, you can create a fairly minimal project (deps.edn file, src/ folder) and rely on io.github.<account>/<project> as the coordinates that the Clojure CLI understands.

If you plan to deploy to Clojars at any point, you'll need to be able to build a JAR file and deploy it. You can learn to do all that manually via tools.build and a build.clj file, and using deps-deploy once you've built the JAR file. It's going to be easier if you use a tool to create a "fully-fleshed" library project for you, that adds all of that configuration for you.

In either case, you're probably going to want to add tests and run them, so you'll either need to add those manually or, again, rely on a tool to set up a project with testing already built in.

For this guide, we're going to use deps-new which can create "batteries-included" library (and application) projects for you.

Installing deps-new

If you already have deps-new installed as a Clojure "tool", as new, then you can skip this section.

The Clojure CLI allows you to install useful tools for your user account so you can use them in any project or even outside projects.

A useful tool to create new projects is deps-new so we're going to install the latest version of that:

clojure -Ttools install-latest :lib io.github.seancorfield/deps-new :as new

Once deps-new is installed as new, we can use clojure -Tnew to create new projects.

Create the Project with deps-new

Bearing in mind the comments about groups and accounts and usernames above, we're going to create our example project with the name:

io.github.clojure-example-library/my-cool-lib

Our project will live on GitHub as https://github.com/clojure-example-library/my-cool-lib and can be used directly from there using the full project name shown above. We will also deploy it to Clojars so that people can depend on it as a JAR file dependency.

Create your new library project. Names are usually hyphen-separated lowercase words:

clojure -Tnew lib :name io.github.clojure-example-library/my-cool-lib
cd my-cool-lib

Typical deps-new usage is clojure -Tnew (lib or app) :name yourname/your-project. If you use just <yourname>, the project coordinates will be assumed to be net.clojars.<yourname>/<your-project>, which is why we used io.github. as a prefix above.

A Note Regarding Project Naming

A line near the top of your build.clj includes something like:

(def lib 'io.github.clojure-example-library/my-cool-lib)

This means that your project has an artifact ID of my-cool-lib, and a group ID of io.github.clojure-example-library.

The artifact ID is the name of your project. The group ID is used to distinguish your my-cool-lib from anyone else's my-cool-lib. It typically identifies the group or organization to which a project belongs.

The maintainers of Clojars require that new libs be published using verified groups, such as org.my-domain or io.github.<account> or net.clojars.<account>.

Read more about groups at https://github.com/clojars/clojars-web/wiki/Groups.

Making the Project your own

Our cool library example project will add a dependency on flatland's "useful" library.

Open up our new deps.edn file and make add our dependency (org.flatland/useful {:mvn/version "0.11.6"}) to the :deps hash map.

In build.clj, remove -SNAPSHOT from version (so it is just "0.1.0").

Licensing

If you created your project using deps-new, it will have added a LICENSE file pertaining to the Eclipse Public License and an explanation at the end of the README.md that this is just a default.

You can choose to license your project however you want. The most common licenses for Clojure libraries (along with grossly oversimplified blurbs, by this author John Gabriele, for each) are:

Another option is the Apache Source License which is a commercial-friendly license (this author Sean Corfield tends to prefer ASL for projects where the default, EPL, is not used).

Whichever one you choose, update your README.md to reflect that choice and save the text of the license as a file named LICENSE in your project directory. Some licenses may encourage you to add a portion of the license text to the header comment in your source files.

Update the README

Aside from providing a good overview, rationale, and introduction at the top, you're encouraged to provide some usage examples as well. A link to the lib's (future) Clojars page (which we'll get to below) might also be appreciated. Add acknowledgements near the end, if appropriate. Adjust the copyright and license info at the bottom of the README as needed.

deps-new provides you with a doc directory and a starter doc/intro.md file. If you find that you have more to say than will comfortably fit into the README.md, consider moving content into the doc directory.

This guide mentions cljdoc.org below as a great option for providing online documentation, so feel free to expand your doc directory per Cljdoc for Library Authors which explains how to provide structure and organization for your documentation.

Other goodies you might include in your README.md or doc/*.md files: tutorial, news, bugs, limitations, alternatives, troubleshooting, configuration.

Note that you generally won't add hand-written API documentation into your README.md or other documentation, as there are tools for creating that directly from your source (discussed later).

Create your project's local git repository

Before going much further, you probably want to get your project under version control. Make sure you've got git installed and configured to know your name and email address (i.e., that at some point you've run git config --global user.name "Your Name" and git config --global user.email "your-email@somewhere.org").

Then, in your project dir, run:

git init
git add .
git commit -m "The initial commit."

At any time after you've made changes and want to inspect them and commit them to the repository:

git diff
git add -p
git commit -m "The commit message."

Write Tests

In test/clojure_example_library/my_cool_lib_test.clj, add tests as needed. An example is provided in there to get you started.

Note: the example test created by deps-new fails deliberately in order for you to get accustomed to writing tests!

Write Code

Write code to make your tests pass.

Remember to add a note at the top of each file indicating copyright (and the license under which the code is distributed, if applicable).

For example:

;; copyright (c) 2023 -- Sean Corfield, all rights reserved.

Run Tests

In your project dir:

clojure -M:test -m cognitect.test-runner

or:

clojure -T:build test

Note: if you didn't use deps-new to create your library project, you'll want to add a :test alias that adds Cognitect's test-runner to your project -- see Configuration in that project's README. The :test alias deps-new generates does not have :exec-fn or :main-opts because it expects you to run tests via the build.clj file, although you can provide -m cognitect.test-runner on the command-line to run tests directly via the CLI, as shown above.

Commit any remaining changes

Before continuing to the next step, make sure all tests pass and you've committed all your changes. Check to see the status of your repo at any time with git status and view changes with git diff.

Complete the GitHub Project Setup and Upload your Code

Once your remote repository has been created, follow the instructions on the resulting page to "Push an existing repository from the command line". You'll of course run the git commands from your project directory:

git remote add origin git@github.com:clojure-example-library/my-cool-lib.git
git push -u origin master

You can now access your online repo. For this tutorial, it's https://github.com/clojure-example-library/my-cool-lib.

Any changes you commit to your local repository can now be pushed to the remote one at GitHub:

# work work work
git add -p
git commit -m "commit message here"
git push

Making a Release on GitHub

At this point, prior to deploying your project to Clojars, it is common to make a release on GitHub describing this new version of your project.

You can update version in build.clj to reflect the new version you want to publish, then add, commit, and push those changes.

On GitHub, navigate to the Releases section of your project and click the icon/button/link to create a new release.

For example, for clojure-example-library/my-cool-lib this would be https://github.com/clojure-example-library/my-cool-lib/releases/new.

Choose a tag that reflects the version you are about to release, e.g., v0.1.0.

Enter the release name or number, e.g., 0.1.0 (it is typically the version without the leading v).

Enter a description, explaining the changes in this version, new features, bug fixes, etc, and create the release.

You should see the release name/number with a tag and a short SHA, e.g.,

0.1.0
... v0.1.0 ec74557

Upload to Clojars

See Publishing to Clojars above to get started. For more info on working with Clojars, see the Clojars wiki.

Run the tests one more time and build the JAR file:

clojure -T:build ci

Once your Clojars account is all set up, upload your library to Clojars like so:

clojure -T:build deploy

If you haven't already setup your environment variables, you can supply them as part of that deploy command -- see deps-deploy usage:

env CLOJARS_USERNAME=username CLOJARS_PASSWORD=clojars-token clojure -T:build deploy

You should now be able to see your lib's Clojars page: for example, https://clojars.org/net.clojars.clojure-example-library/my-cool-lib!

Note: to deploy that example library, the lib var inside build.clj was changed to net.clojars.clojure-example-library/my-cool-lib which is a default verified group name, to avoid verifying via GitHub, since clojure-example-library is a GitHub organization rather than an individual account. If you use your GitHub username to login to Clojars to verify your account, you can use io.github.<username>.

If everything goes smoothly, all of the links on that Clojars page should work and clicking this git tree in the Pushed by section should take you to GitHub, showing the source code at that version, e.g., https://github.com/clojure-example-library/my-cool-lib/tree/v0.1.0

In addition, if you clicked on the cljdoc link on that Clojars page, it will take you to a page where you can build the API docs for your library. Once that build has completed, you should be able to visit the generated documentation, e.g., https://cljdoc.org/d/net.clojars.clojure-example-library/my-cool-lib/0.1.0/doc/readme

See the next section for more details.

Generate API docs (optional)

For larger library projects, you may want to automatically generate API docs (from your docstrings). See cljdoc for the most common, automated documentation site used for Clojure libraries.

If you've followed all the steps above, that should go smoothly, but if you get into trouble, the #cljdoc channel on the Clojurians Slack is a great place to get help.

Announce (optional)

You're welcome to announce the availability of your new library wherever you choose -- e.g., on Clojurians Slack, Twitter, Mastodon, the Clojure mailing list, r/Clojure (Reddit), ClojureVerse. Just make sure to follow the etiquette about announcements, wherever you post!

Make Updates to your library

Making updates to your lib follows the same pattern as described above:

# work test work test
# document the updates in CHANGELOG.md
# update the version in README.md
# update version string in build.clj
git add -p
git commit
git push
# make a new release on GitHub for this new version

# final testing and build the JAR file
clojure -T:build ci
# deploy to Clojars
clojure -T:build deploy

And optionally announce the release (Clojurians Slack prefers that you use #releases for small, frequent announcements, and only use #announcements for an initial release and then only about once a month for major releases or "round-up" announcements of multiple releases).

Merging pull-requests

Note that if you receive a pull-request at github, you can easily merge those changes into your project (right there, via the web page describing the pull-request). Afterwards, update your local repo to grab those changes as well:

git pull

See Also

For more detailed documentation on various aspects of the procedures described here, see:

Contributors

John Gabriele jmg3000@gmail.com (original author) Sean Corfield sean@corfield.org (updated to use Clojure CLI)