Sorry for posting again. I really need to proof-read better. Please ignore the prior email.
I have recently had quite an adventure modifying several of Log4j’s Maven modules to implement JPMS on our master branch. It was an adventure due to a few issues: 1. https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8265826 <https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8265826>. This bug has been fixed in Java 17 but Log4j uses Java 11 to build. 2. Log4j-plugins builds an annotation processor, packages it with the annotations and classes necessary to build and run plugins, creates and test jar and runs unit tests. 3. It is not possible to compile an annotation processor with a module-info.java present. The compile will fail because it can’t find the annotation processor “service” when compiling module-info.java. 4. It is very difficult to compile an annotation processor and then use it in the same Maven module. JPMS expects the annotation processor to either be on the classpath or specified with the processorpath option. When a module-info.java is present, Maven automatically moves everything to the module path. Maven only supports using coordinates to specify the processor path, which don’t exist when the processor is in the same module. The only way to solve this is to compile all the classes with proc=only without a module-info.java present. 5. Although number 4 might seem bad, it really doesn’t matter because javac will fail if a module-info.java is present because module-info.java will have a reference to the service class being generated by the annotation processor and for some reason module-info.java is resolved before the annotation processor runs. 6. If the main set of classes are compiled with a module-info.java every other compile in the Maven module must also be modularized. Likewise, if the main module does not contain a module-info.java no other compile can either. 7. JPMS requires that every module have its own package space with no overlap with any other JPMS module. So while generating the log4j-plugins module is quite painful, generating log4j-core isn’t much better. That is actually the primary focus for this list. Log4j-core consists of the main classes packaged in the jar, a test jar that is used by downstream Maven modules, and the unit tests. Prior to JPMS one would just create the main jar and then package all the test classes and unit tests in a test jar. This can no longer be done with JPMS. When a project publishes a test jar along with the main jar, just like any other JPMS module. the test jar cannot use the package space of the main classes. Log4j core uses org.apache.logging.log4j.core so I placed all the test utility classes under org.apache.logging.log4j.core.test. However, the unit tests all need to be packaged in the main package space since its module-info.java “extends” the main module and several unit tests are required to be in the same main package so that they can access package private methods specifically provided for testing. In order to get this to work I had to perform the following steps: • Compile all the main classes except module-info.java with the Plugin annotation processor. • Compile the main module-info.java. • Compile the test classes used by other modules with module-info.java and using the plugin preprocessor. • Package these test classes in a test jar. • Delete the module-info and generated source for the test classes. • Move the main module-info to a temp location. • Compile the unit test classes without module-info.java. • Move the main module-info back to the classes directory. • Compile module-info.java for unit tests. • Run the unit tests. • Create the main jar if the unit tests pass. Were it not for JDK-8265826 I believe this could have been simplified somewhat to: • Compile all the main classes except module-info.java with the Plugin annotation processor. • Compile the main module-info.java. • Compile the test classes used by other modules with its module-info.java and using the plugin preprocessor. • Package these test classes in a test jar. • Delete the module-info and generated source for the test classes. • Compile the unit test classes with its module-info.java. • Compile module-info.java for unit tests. • Run the unit tests. • Create the main jar if the unit tests pass. So the gist of this entire email is pretty simple. Is there a way Maven could be modified to better support creating test jars with JPMS? Ralph
