Pomegranate

Pomegranate is a library that provides:

1. A sane Clojure API for Maven-resolver (originally called Aether).
2. A re-implementation of add-classpath (deprecated in Clojure core) that:

• is a little more comprehensive than core's add-classpath — it should work as expected in more circumstances, and
• optionally uses Maven-resolver to add a Maven artifact (and all of its transitive dependencies) to your Clojure runtime's classpath dynamically.

Insofar as most useful Clojure libraries have dependencies, any reasonable implementation of the add-classpath concept must seamlessly support resolving those dependencies IMO.

"Installation"

Pomegranate is available in Maven central. Add it to your Leiningen project.clj:

[clj-commons/pomegranate "1.2.1"]

add-classpath usage

Just to set a stage: you're at the REPL, and you've got some useful data that you'd like to munge and analyze in various ways. Maybe it's something you've generated locally, maybe it's data on a production machine and you're logged in via nREPL. In any case, you'd like to work with the data, but realize that you don't have the libraries you need do what you want. Your choices at this point are:

1. Dump the data to disk via pr (assuming it's just Clojure data structures!), and start up a new Clojure process with the appropriate libraries on the classpath. This can really suck if the data is in a remote environment.
2. There is no second choice. You could use add-claspath, but the library you want has 12 bajillion dependencies, and there's no way you're going to hunt them down manually.

Let's say we want to use Incanter (which has roughly 40 dependencies — far too many for us to reasonably locate and add via add-classpath manually):

=> (require '(incanter core stats charts))
#<CompilerException java.io.FileNotFoundException:
  Could not locate incanter/core__init.class or incanter/core.clj on classpath:  (NO_SOURCE_FILE:0)>

Looks bleak. Assuming you've got Pomegranate on your classpath already, you can do this though:

=> (use '[cemerick.pomegranate :only (add-dependencies)])
nil
=> (add-dependencies :coordinates '[[incanter "1.9.2"]]
                     :repositories (merge cemerick.pomegranate.aether/maven-central
                                          {"clojars" "https://clojars.org/repo"}))
;...add-dependencies returns full dependency graph...
=> (require '(incanter core stats charts))
nil

Now you can analyze and chart away, Incanter having been added to your runtime. Note that add-dependencies may crunch along for a while — it may need to download dependencies, so you're waiting on the network. All resolved dependencies are stored in the default local repository (~/.m2/repository), and if they are found there, then they are not downloaded.

The arguments to add-dependencies look like Leiningen-style notation, and they are.

Please note that there are a number of scenarios in which add-dependencies will not work, or will not work as you'd expect. Many of these are due to the nature of JVM classloaders (e.g. adding jars containing conflicting versions of a particular dependency will rarely end well), which Pomegranate does not currently attempt to hide. Thus, add-classpath and add-dependencies should be considered escape hatches to be used when necessary, rather than a regular part of your development workflow.

URLClassLoader modifiability

Starting with pomegranate 1.0.0, java.net.URLClassLoaders are not modifiable by default. This is to accommodate new reflection policy starting with JDK 9 (which currently issues an ugly warning on reflective access to non-public methods, but future releases will simply fail). If you are in a situation where you are using pomegranate but do not have a clojure.lang.DynamicClassLoader visible in your classloader hierarchy, you will need to explicitly enable the java.net.URLClassLoader support in dynapath (upon which pomegranate relies for such things).

Status of Aether support

Pomegranate is being used by Leiningen v2.x as its sole dependency resolution library. This has prompted rapid maturation of the scope and quality of Aether support. That said, specific API points remain subject to change as we find the right abstractions and conventions.

Supported features

• dependency resolution
  • common dependency graph/hierarchy manipulation ops
• local installation
• remote deployment
• repository authentication for all of the above
• HTTP proxy configuration
• offline mode
• transfer listeners (with a sane Clojure fn veneer)

Not there yet

• repository listeners
• options to retrieve a single artifact (e.g. for obtaining source/javadoc)
• tests; there's halfway decent coverage, but nowhere near the kind of comprehensive combinatorial testing that maven dependency resolution demands

Changelog

See the CHANGES.md file at the top level of the repo.

License

Copyright © 2011-2017 Chas Emerick and all other contributors.

Licensed under the EPL. (See the file epl-v10.html.)