Relocated dependencies don't show up in lein deps :tree

[plexus]

Initial debugging steps

• Updating to using the latest released version of Leiningen (lein upgrade).
• Moving your ~/.lein/profiles.clj (if present) out of the way. This contains third-party dependencies and plugins that can cause problems inside Leiningen.
• Updating any old versions of plugins in your project.clj, especially if the problem is with a plugin not working. Old versions of plugins like nREPL and CIDER (as well as others) can cause problems with newer versions of Leiningen.
• (If you are using Java 9 or newer), updating your dependencies to their most recent versions. Recent JDK's have introduced changes which can break some Clojure libraries.

Describe the bug

Maven has a feature called "relocation" where a pom for a given artifact can signal that this artifact has relocated to a different groupId. This acts as kind of redirect, for instance if you depend on org.hibernate/hibernate-validator, then this will actually end up using org.hibernate.validator/hibernate-validator, because of this stanza in the pom.xml:

    <distributionManagement>
        <relocation>
            <groupId>org.hibernate.validator</groupId>
        </relocation>
    </distributionManagement>

This in itself works fine, the new artifact will be downloaded and added to the classpath, but it will not get listed when calling lein deps :tree.

To Reproduce
Steps to reproduce the behavior:

project.clj:

(defproject relocation-test "0.1.0-SNAPSHOT"
  :dependencies [[org.hibernate/hibernate-validator "7.0.1.Final"]])

and invoke lein deps :tree

result:

Actual behavior

$ lein deps :tree
 [clojure-complete "0.2.5" :exclusions [[org.clojure/clojure]]]
 [nrepl "0.8.3" :exclusions [[org.clojure/clojure]]]

Side note, I have verified with clojure.java.classpath that hibernate-validator is indeed on the classpath:

/home/arne/.m2/repository/org/hibernate/validator/hibernate-validator/7.0.1.Final/hibernate-validator-7.0
.1.Final.jar

Expected behavior

$ lein deps :tree
 [clojure-complete "0.2.5" :exclusions [[org.clojure/clojure]]]
 [nrepl "0.8.3" :exclusions [[org.clojure/clojure]]]
 [org.hibernate.validator/hibernate-validator "7.0.1.Final"]

Environment

• Leiningen Version: 2.9.6
• Leiningen installation method: manual
• JDK Version: openjdk version "11.0.7" 2020-04-14
• OS: Ubuntu 21.04

Additional context

This is prompted by clojars/clojars-web#801 and lambdaisland/open-source#2. Due to the new Clojars policies around group id naming there is some interest in Maven's relocation support, and we are looking at what the support is across tools.

[technomancy]

Happy to take a patch for this.