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Asked: 2026-05-30T10:06:35+00:00

After upgrading Leiningen (from v1.6 to v1.7) with lein upgrade command lein swank stopped

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After upgrading Leiningen (from v1.6 to v1.7) with lein upgrade command lein swank stopped working with error message: 

Exception in thread "main" java.lang.NoClassDefFoundError:  
Caused by: java.lang.ClassNotFoundException:  
[...] 
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class:  .  Program will exit.

Since I tried it from command line, I believe Emacs configuration doesn’t matter in this case. So I tried to re-install Leiningen completely. What I’ve done (using suggestions from here and error messages): 

rm -R ~/.m2
# rm ~/.lein/plugins/*  
lein self-install

(I used second line on second reinstallation only, so it is here for the sake of completeness)

Then I created new project and installed lein-swank plugin, since, as far as I understand, it is recommended way at the moment: 

lein new test-project
lein plugin install swank-clojure 1.4.0  # I tried earlier version (1.3.2) too

And finally started lein swank with:

cd test-project
lein swank

But got same error as before.

So my questions are:

  1. How to fix this problem?
  2. Do I reinstall Leiningen correctly or some steps are missing?

UPD. Here’s project.clj generated with new project:

(defproject test-project "1.0.0-SNAPSHOT"
   :description "FIXME: write description"
   :dependencies [[org.clojure/clojure "1.3.0"]])
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1 Answer

  1. Editorial Team

    Does the swank-clojure troubleshooting page help:

    Troubleshooting

    Currently having multiple versions of swank-clojure on
    the classpath can cause issues when running lein swank or lein
    jack-in. It’s recommended to not put swank-clojure in your
    :dev-dependencies but run lein plugin install to have it installed
    globally for all projects instead. This also means that people hacking
    on your project won’t have to pull it in if they are not Emacs users.

    It’s also possible for some packages to pull in old versions of
    swank-clojure transitively, so check the lib/ directory if you are
    having issues. In particular, Incanter is known to exhibit this
    problem. Judicious use of :exclusions make it work:

    :dependencies [[incanter "1.2.3" :exclusions [swank-clojure]]]

    Since swank-clojure 1.3.4, having versions of clj-stacktrace older
    than 0.2.1 in your project or user-level plugins will cause Unable to
    resolve symbol: pst-elem-str errors. Keep in mind that user-level
    plugins in ~/.lein/plugins are uberjars in Leiningen 1.x, so it’s
    possible that one of your plugins (such as lein-difftest before
    version 1.3.7) contains an old clj-stacktrace even if it doesn’t have
    its own file there. Specifying a newer version should be enough if
    you’re having trouble:

    :dependencies [[clj-stacktrace "0.2.4"]]
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