Unable to resolve module using --module-source-path

Question

Following up on How to define qualified exports to unknown modules? I've posted a testcase with two modules: core and plugin.

core tries to expose a package to plugin using qualified exports but the compiler complains that plugin does not exist. Following up on Alan Bateman's recommendation, I tried adding --module-source-path <path-of-plugin> --module plugin pointing from core to plugin but the compiler complains:

module plugin not found in source path

Why isn't the compiler able to find module plugin?

Answer 1

I figured it out through trial and error.

1. Use --module-source-path ${project.basedir}/../*/src/main/java to make sure the compiler can see the source-code of both modules.
2. Use --module core to make sure that the compiler only builds core in spite of seeing all modules.
3. Tell maven-jar-plugin to package classes from classes/${module.name} instead of just classes because module-source-path causes the output to be prefixed by the module name. I have not found a way to disable this prefix.

The fixed code can be found at https://bitbucket.org/cowwoc/qualified-exports-testcase/

Caveat: This technique only works if the module directory name (the component resolved by *) matches the Java module name. In this particular example the module core had its sources in directory core/src/main/java. If, on the other hand, the directory name was core but the corresponding Java module was org.bitbucket.core then the compilation would fail with module org.bitbucket.core not found in module source path.