Pass argument to leiningen readable by project.clj

Question

I have a project.clj file that I want to use differently depending on an argument passed in when called by leiningen. Here is my hypothetical sample project

(defproject simple "0.0.1"
  :source-paths [(get-argument "source.path")])

(In this case get-argument would simply call System/getProperty). I would use this file like this,

lein2 compile -Dsource.path=path/to/location

The problem is two-fold,

• I don't know how to pass an argument to leiningen. It doesn't accept the -Dkey=value syntax. I couldn't find anything in documentation about passing optional/extra arguments. Am I missing something obvious?
• The subforms inside defproject seem to be handled a special way. I couldn't find an easy way to put code into it.

I have found some approaches

• https://github.com/weavejester/environ looks promising, but it seems to work only in proper clojure code, not inside project.clj
• https://groups.google.com/forum/?fromgroups=#!topic/leiningen/t8G6Et1_j8w -- this is a workaround that may solve half of the problem
• What is an elegant way to set up a leiningen project that requires different dependencies based on the build platform? gives some idea how to eval code in project.clj
• https://github.com/sattvik/leinjacker promises to do some dirty tricks, but I couldn't make it work in my environment

(What I actually want to use it for is that I have a clojurescript project with different artifacts. While it's possible to configure different builds for it, they all share the same crossovers.)

Answer 1

One approach that is convenient on unix-like platforms is to use an environment variable, combined with lein's willingness to evaluate expressions marked with a tilde in project.clj files. So for your example, you could provide a project.clj like:

(defproject simple "0.0.1"
  :source-paths [~(System/getenv "MY_SRC_PATH")]
  :dependencies [[org.clojure/clojure "1.5.0"]])

...then set the environment variable when launching lein like this:

MY_SRC_PATH="s2" lein compile

I don't know how well this approach would work on Windows.