For a lein project, why is lib/ in .gitignore?

Question

I'm relatively new to Clojure and Java. Why is the lib folder in a lein project not added to the git repo of a lein project? I would think it that would be convenient to have all the necessary jars there for distributed development.

Answer 1

In a Leiningen project, the project.clj file dictates the project's dependencies, and when you run 'lein deps', all dependencies listed in the project.clj file are downloaded to lib/. Therefore, there's no need to check in the jars because the project.clj in combination with the 'lein deps' command is all that's necessary for another person to reproduce the same lib/ that you have. Checking in all the jars is redundant and a waste of space.

Moreover, as mblinn points out, it's better to pull jars from artifact repositories designed for the purpose of distributing and updating dependencies, rather than constantly changing and committing new jars whenever a dependency gets updated. This is especially true when your project depends on snapshot jars, which are subject to frequent change; if you checked in the jars, you'd have to check in a new jar every time the snapshot gets updated, but if you rely on 'lein deps' to pull jars from artifact repos, then you'll stay up to date with no effort. But even for non-snapshot jars, updating a dependency by changing its version in project.clj and then running 'lein deps' is a lot easier and faster than manually placing the jar in lib/ and checking it in.

I hope the above explanation was accessible. If not, and you don't understand some of the concepts discussed, like artifact repositories or dependencies, let me know and I'll explain.