5.5 KiB
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 deploy guide
explains how to set up a private repository. If you are not sharing
them with a team you could also just
install locally.
In general it's easiest to deploy them to a private S3 bucket with
the s3-wagon-private plugin.
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.
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 lein deps :tree 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
swank-clojure or
VimClojure, 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: Why is Leiningen 2 still in a preview release?
A: As of the preview3 release, Leiningen 2 is very stable and
recommended for general use. The main thing keeping it from a final
release is the fact that the current Clojars repository
mingles snapshots with releases,
which is undesirable. Since switching the default repositories to a
releases-only Clojars (which is still in development) would be a
breaking change, a series of previews is being released in the mean time.