98 lines
5.1 KiB
Markdown
98 lines
5.1 KiB
Markdown
# FAQ
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**Q:** How do you pronounce Leiningen?
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**A:** It's LINE-ing-en. ['laɪnɪŋən]
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**Q:** What's a group ID? How do snapshots work?
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**A:** See the
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[tutorial](https://github.com/technomancy/leiningen/blob/preview/doc/TUTORIAL.md)
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for background.
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**Q:** How should I pick my version numbers?
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**A:** Use [semantic versioning](http://semver.org).
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**Q:** What if my project depends on jars that aren't in any repository?
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**A:** The [deploy guide](https://github.com/technomancy/leiningen/blob/preview/doc/DEPLOY.md)
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explains how to set up a private repository. If you are not sharing
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them with a team you could also just
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[install locally](https://github.com/kumarshantanu/lein-localrepo).
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In general it's easiest to deploy them to a private S3 bucket with
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the [s3-wagon-private](https://github.com/technomancy/s3-wagon-private) plugin.
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**Q:** I want to hack two projects in parallel, but it's annoying to switch between them.
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**A:** If you create a directory called `checkouts` in your project
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root and symlink some other project roots into it, Leiningen will
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allow you to hack on them in parallel. That means changes in the
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dependency will be visible in the main project without having to go
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through the whole install/switch-projects/deps/restart-repl cycle,
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and the copy in `checkouts` will take precedence over the dependency
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declared in project.clj. Note that this is not a replacement for
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listing the project in `:dependencies`; it simply supplements that for
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convenience.
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**Q:** Is it possible to exclude indirect dependencies?
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**A:** Yes. Some libraries, such as log4j, depend on projects that are
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not included in public repositories and unnecessary for basic
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functionality. Projects listed as `:dependencies` may exclude
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any of their dependencies by using the `:exclusions` key. See
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`lein help sample` for details.
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**Q:** Why doesn't `deps` task populate the `lib` directory in version 2?
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**A:** The only reason version 1 copied the jars around in the first
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place was to support existing tooling that needed a cheap way to
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calculate a project's classpath. Now that Leiningen has a mature
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plugin ecosystem, this is no longer needed; jars can be referenced
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directly out of the `~/.m2/repository` directory. If you need to see
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a listing of all the dependencies that will be used and their
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versions, use `lein deps :tree`.
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**Q:** What does `java.lang.NoSuchMethodError: clojure.lang.RestFn.<init>(I)V` mean?
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**A:** It means you have some code that was AOT (ahead-of-time)
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compiled with a different version of Clojure than the one you're
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currently using. If it persists after running `lein clean` then it
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is a problem with your dependencies. Note that for
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your own project that AOT compilation in Clojure is much less
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important than it is in other languages. There are a few
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language-level features that must be AOT-compiled to work, generally
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for Java interop. If you are not using any of these features, you
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should not AOT-compile your project if other projects may depend
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upon it.
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**Q:** I'm behind an HTTP proxy; how can I fetch my dependencies?
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**A:** Set the `$http_proxy` environment variable in Leiningen 2.x.
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For Leiningen 1.x versions, see the instructions for
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[configuring a Maven proxy](http://maven.apache.org/guides/mini/guide-proxies.html)
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using `~/.m2/settings.xml`.
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**Q:** What can be done to speed up launch?
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**A:** The main delay involved in Leiningen comes from starting the
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JVM. Most people use a development cycle that involves keeping a
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single REPL process running for as long as you're working on that
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project. Depending on your editor you may be able to do this via its
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Clojure integration. (See
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[swank-clojure](http://github.com/technomancy/swank-clojure) or
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[VimClojure](https://bitbucket.org/kotarak/vimclojure), for
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example.) Otherwise you can use the basic `lein repl`.
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**Q:** Still too slow; what else can make startup faster?
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**A:** If you are running an older version of Leiningen (before 1.7)
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you can `export LEIN_JVM_OPTS=-XX:+TieredCompilation` to improve
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boot time. This requires Hotspot version 20 or newer. On newer versions
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of Leiningen it is enabled automatically.
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**Q:** Why is Leiningen 2 still in a preview release?
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**A:** As of the preview3 release, Leiningen 2 is very stable and
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recommended for general use. The main thing keeping it from a final
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release is the fact that the current Clojars repository
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[mingles snapshots with releases](https://github.com/ato/clojars-web/issues/24),
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which is undesirable. Since switching the default repositories to a
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releases-only Clojars (which is still in development) would be a
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breaking change, a series of previews is being released in the mean time.
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**Q:** I don't have access to stdin inside my project.
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**A:** This is a limitation of the JVM's process-handling methods;
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none of them expose stdin correctly. This means that functions like
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`read-line` will not work as expected in most contexts, though the
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`repl` task necessarily includes a workaround. You can also use the
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`trampoline` task to launch your project's JVM after Leiningen's has
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exited rather than launching it as a subprocess.
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