mvn fails to start properly on default installation

[Joshua Haase]

Description: Ubuntu 22.04.3 LTS
Release: 22.04

I just installed maven from the default repository to build a java project.
Running mvn command I get the following error:

```
$ mvn
Error: Could not find or load main class org.codehaus.plexus.classworlds.launcher.Launcher
Caused by: java.lang.ClassNotFoundException: org.codehaus.plexus.classworlds.launcher.Launcher
```

I executed the maven launch script with the appropriate `JAVA_HOME` and `MAVEN_HOME`:

```
$ env JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 MAVEN_HOME=/usr/share/maven bash -x mvn
• exec /usr/lib/jvm/java-17-openjdk-amd64/bin/java -classpath '/current-working-directory/boot/plexus-classworlds-.jar' -Dclassworlds.conf=/current-working-directory/bin/m2.conf -Dmaven.home=/current-working-dire ctory -Dlibrary.jansi.path=/current-working-directory/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/current-working-directory/ org.codehaus.plexus.classworlds.launcher.Launcher
Error: Could not find or load main class org.codehaus.plexus.classworlds.launcher.Launcher
Caused by: java.lang.ClassNotFoundException: org.codehaus.plexus.classworlds.launcher.Launcher
```

The program should identify the correct MAVEN_HOME instead of trying to use my current working directory.
I can run maven manually using this command, but I would not expect having to diagnose this issue with a package from the official repositories.

```
$ /usr/lib/jvm/java-17-openjdk-amd64/bin/java \
  -classpath /usr/share/maven-repo/:/usr/share/java/:/usr/share/java/plexus-classworlds.jar \
  -Dmaven.home=/usr/share/maven \
  -Dclassworlds.conf=/usr/share/maven/bin/m2.conf \
  -Dlibrary.jansi.path=/usr/share/maven/lib/jansi.jar \
  -Dmaven.multiModuleProjectDirectory=$(pwd) \
  org.codehaus.plexus.classworlds.launcher.Launcher
```

---
External link: https://warthogs.atlassian.net/browse/PEL-634

[Joshua Haase (xihh)]

It seems like the program assumes it will be called using the absolute path to the command, the folowing command runs:

JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-amd64 /usr/share/maven/bin/mvn

[Vladimir Petko (vpa1977)]

This is an upstream issue present in the current master branch of maven. The code in mvn does not resolve the path to the mvn shell script[1].

[1] https://github.com/apache/maven/blob/master/apache-maven/src/assembly/shared/mvnvalidate

[Maarten Mulders (mthmulders)]

I see that Ubuntu ships version 3.8.7 of Maven. Even if the issue is upstream, I don't think it's very likely to get fixed. The Maven team has released quite a few 3.9.x releases already and is working towards 4.x [1]. My guess is that if the issue is indeed in the Maven code base, it will not receive a lot of attention.

[1] https://maven.apache.org/docs/history.html