5.1 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: If you create a directory called checkouts
in your project
root and symlink some other project roots into it, Leiningen will
allow you to hack on them in parallel. That means changes in the
dependency will be visible in the main project without having to go
through the whole install/switch-projects/deps/restart-repl cycle,
and the copy in checkouts
will take precedence over the dependency
declared in project.clj. Note that this is not a replacement for
listing the project in :dependencies
; it simply supplements that for
convenience.
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'm behind an HTTP proxy; how can I fetch my dependencies?
A: Set the $http_proxy
environment variable in Leiningen 2.x.
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: If you are running an older version of Leiningen (before 1.7)
you can export LEIN_JVM_OPTS=-XX:+TieredCompilation
to improve
boot time. This requires Hotspot version 20 or newer. On newer versions
of Leiningen it is enabled automatically.
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.
Q: I don't have access to stdin inside my project.
A: This is a limitation of the JVM's process-handling methods;
none of them expose stdin correctly. This means that functions like
read-line
will not work as expected in most contexts, though the
repl
task necessarily includes a workaround. You can also use the
trampoline
task to launch your project's JVM after Leiningen's has
exited rather than launching it as a subprocess.