Improve separate compilation of module-info.java

I implemented compileModuleInfoJava task by making its destinationDir to be the same as that of compileJava task. Since then, I learned (thx, @sormuras!) that Gradle task shouldn’t share the same output directories (it’s problematic e.g. for cleaning or caching).

A much cleaner solution would be to change this: https://github.com/java9-modularity/gradle-modules-plugin/blob/44a76f62965d93a45422f62f16fb75ef6e3fe13d/src/main/java/org/javamodularity/moduleplugin/tasks/CompileModuleInfoTask.java#L60-L62

to sth like this:

        compileModuleInfoJava.setClasspath(project.files(compileJava.getDestinationDir()));
        compileModuleInfoJava.setSource(pathToModuleInfoJava());
        compileModuleInfoJava.setDestinationDir(/* e.g. `build/module-info` */);

and then making the Jar task include the destinationDir of compileModuleInfoJava task.

It’s based on what @sormuras did while implementing https://github.com/junit-team/junit5/pull/1857: https://github.com/junit-team/junit5/blob/8484eaeff1e0bbd4536ff262c2394972945296cf/buildSrc/src/main/kotlin/java-library-conventions.gradle.kts#L85-L93

[siordache]

Thanks for the great analysis, Tomasz! Option 2.b is my favorite. I will implement it in the next couple of days.

[tlinkowski]

Ha, so it’s actually much harder than I assumed… Thanks for your excellent research and work, Serban!

I read what you linked. As I see it now, we have the following two options (correct me if I’m wrong):

1. [Compile+Run] Compile everything (Kotlin, Java, Groovy, module-info - in that order) into a single directory so that “module-info” sees all the packages when we compile and then test/run
   • pros: simple
   • cons: hard to clean, hard to cache by Gradle
2. [Compile] Compile everything separately using the --patch-module trick (nice!) [Run] “Merge” the output into a separate single directory (e.g. build/classes/merged) for the purposes of test and run tasks
   • pros: separate dirs can be cleaned & cached in Gradle
   • cons: more complicated - I see two options here
     1. test and run mark those separate dirs as their input (build/classes/java|kotlin|groovy|module-info), and only during doFirst, for their internal purposes, they perform: 1) purging build/classes/merged (in case it contains something stale), 2) copying contents of build/classes/java|kotlin|groovy|module-info into build/classes/merged
     2. we introduce a separate task of type Sync, named e.g. mergeClasses, on which run and test depends, and which:
        • depends on: compileKotlin, compileJava, compileGroovy, compileModuleInfoJava
        • inputs (from): separate dirs (build/classes/java|kotlin|groovy|module-info)
        • output (into): build/classes/merged
        • thanks to having a separate task, we leave it to Gradle to determine if build/classes/merged has anything stale or not

To sum up, I think I still prefer option 2 over option 1, and as I can’t think of anything better than copying, I tried to analyze how to approach this copying best.