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FAQ
Q: How do you pronounce Leiningen? A: It's LINE-ing-en. ['laɪnɪŋən]
Q: What's a group ID? How do snapshots work? A: See the tutorial for background.
Q: How should I pick my version numbers? A: Use semantic versioning.
Q: What if my project depends on jars that aren't in any repository? A: The best thing to do is to get them in a repository. The deploy guide explains how to set up a private repository. In general it's easiest to deploy them to a static HTTP server or a private S3 bucket with the s3-wagon-private plugin. If you are just doing exploratory coding and not collaborating with a team you could install locally.
Q: I want to hack two projects in parallel, but it's annoying to switch between them. A: Leiningen provides a feature called checkout dependencies. See the tutorial to learn more.
Q: Is it possible to exclude indirect dependencies?
A: Yes. Some libraries, such as log4j, depend on projects that are
not included in public repositories and unnecessary for basic
functionality. Projects listed as :dependencies
may exclude
any of their dependencies by using the :exclusions
key. See
lein help sample
for details.
Q: Why doesn't deps
task populate the lib
directory in version 2?
A: The only reason version 1 copied the jars around in the first
place was to support existing tooling that needed a cheap way to
calculate a project's classpath. Now that Leiningen has a mature
plugin ecosystem, this is no longer needed; jars can be referenced
directly out of the ~/.m2/repository
directory. If you need to see
a listing of all the dependencies that will be used and their
versions, use lein deps :tree
. To get the classpath use lein classpath
.
Q: What does java.lang.NoSuchMethodError: clojure.lang.RestFn.<init>(I)V
mean?
A: It means you have some code that was AOT (ahead-of-time)
compiled with a different version of Clojure than the one you're
currently using. If it persists after running lein clean
then it
is a problem with your dependencies. Note that for
your own project that AOT compilation in Clojure is much less
important than it is in other languages. There are a few
language-level features that must be AOT-compiled to work, generally
for Java interop. If you are not using any of these features, you
should not AOT-compile your project if other projects may depend
upon it.
Q: I specified a dependency on version X but am getting version Y; what's up?
A: One of your dependencies' dependencies has declared a
dependency on a hard version range, which overrides your "soft"
declaration. If you change yours to a hard version range, it will
refuse to function due to conflicts, so it's best to find the
dependency that's at fault via the
lein-pedantic plugin and
add an :exclusions
clause to it. See lein help sample
for how
exclusions work. You may also want to report a bug with the
dependency that uses hard version ranges as they cause all kinds of
problems and exhibit unintuitive behaviour.
Q: I'm behind an HTTP proxy; how can I fetch my dependencies?
A: Set the $http_proxy
environment variable in Leiningen 2.x. You can also
set $http_no_proxy
for a list of hosts that should be reached directly, bypassing
the proxy. This is a list of patterns separated by |
and may start or end with
a *
for wildcard, e.g. localhost|*.mydomain.com
.
For Leiningen 1.x versions, see the instructions for
configuring a Maven proxy
using ~/.m2/settings.xml
.
Q: What can be done to speed up launch?
A: The main delay involved in Leiningen comes from starting the
JVM. Most people use a development cycle that involves keeping a
single REPL process running for as long as you're working on that
project. Depending on your editor you may be able to do this via its
Clojure integration. (See
nrepl.el or
foreplay, for
example.) Otherwise you can use the basic lein repl
.
Q: Still too slow; what else can make startup faster?
A: The trampoline
task uses Leiningen to calculate the command
needed to launch your project and then allows Leiningen's JVM to
exit before launching your project. Exporting the
$LEIN_FAST_TRAMPOLINE
environment variable allows the command to
be cached, making it possible to skip launching the Leiningen JVM
entirely. You can set this on a per-project variable by creating a
.lein-fast-trampoline
file in the project root. In addition, you
can usually set :bootclasspath true
in project.clj to speed up
project launches, though there are compatibility issues with some
libraries.
Q: It looks like a different set of dependencies are being used in
the repl vs other tasks.
A: The repl needs to add a few extra implicit dependencies in
order to function. For instance, it needs to load an
nREPL server, and it loads
a client for fetching
ClojureDocs examples, both which have
dependencies that could interfere with the dependencies declared in
your own project. You can declare a :leiningen/reply
profile to
override the clojuredocs client dependencies. While you can't run
the repl task without nREPL in the dependencies, specifying your own
version of it will override the version Leiningen adds. Another way
around the problem would be to load a bare repl by invoking lein trampoline run -m clojure.main/repl
, though you may want to use
rlwrap
on that to get proper key bindings and history.