javac compiler doesn't support --processor-module-path

[ghost]

Maven builds fail if the following conditions are set:

• Using Java 9 or 10
• Using module-info.java
• Build depends on the execution of annotation processors (like Lombok)

This results in using the module path instead of the class path of the javac compiler. Now the javac compiler also needs to be configured with --processor-module-path so that the compiler can find the required annotation processors in the processor module path. The latest version of plexus-compiler-javac only supports the --processorpath parameter of javac. This parameter is set by the maven-compiler-plugin to the default class path. But when using Java 9+ modules the class path doesn't seem to be used by javac to find the annotation processors. So, to use annotation processors in combination with Java 9+ modules, the plexus-compiler-javac needs to support the related parameter.

[scholzi100]

I reproduced the problem with Java 12 too. --processor-module-path should be used with Java 9+ and only when a module-info file is created. There is also a related MCOMPILER-310.

Hotfix: set all processors manually in the annotationProcessors section of maven-compiler-plugin.