Add easy support for automatic module name

[dmlloyd]

New feature, improvement proposal

It would be nice if there was a configuration property to easily set the automatic module name of a JAR, since this is a very frequent activity when migrating projects to use modules. It should print a warning (and do nothing) if a module descriptor is found in the project.

I have a patch to do this, which I will propose in a PR forthwith.

Thanks!

[desruisseaux]

The current plugin allows the following:

<configuration>
  <archive>
    <manifestEntries>
      <Automatic-Module-Name>org.foo.bar</Automatic-Module-Name>
    </manifestEntries>
  </archive>
</configuration>

The pull requests #521 and #522 would allow to get the same result with the following, except for the warning when a module-info.class is present:

<configuration>
  <automaticModuleName>org.foo.bar</automaticModuleName>
</configuration>

This is admittedly shorter, but is it worth to have two places for configuring the same attribute in the plugin configuration?

If, nevertheless, there is a desire to handle the Automatic-Module-Name attribute in a special way, if we want to be consistent with other attributes that are handled in a special way such as Main-Class, then the attribute would need to be added in org.apache.maven.shared.archiver.ManifestConfiguration. The XML fragment would become like below:

<configuration>
  <archive>
    <manifest>
      <automaticModuleName>org.foo.bar</automaticModuleName>
    </manifest>
  </archive>
</configuration>

Note that this is not really shorter than the existing.

[dmlloyd]

All your points are valid; my goal however isn't (only) less typing. I want to be able to supply an automatic module name using just a build property, e.g. -Dmaven.jar.automaticModuleName=org.foo.myproject (or more likely, a value at the top of my POM).

This cannot really be done in the obvious way with the archiver configuration because IIUC if a property expression has an empty value, then the value will be an empty string, causing an empty Automatic-Module-Name property to be added to the manifest.

The convenience is, I'd say, about equivalent to that of detectMultiReleaseJar which is also defined at this level rather than the archiver level.

(That said, I see I ironically forgot to account for the empty string in my PRs, so I'll fix that now.)