Actually fix lemminx compilation

[datho7561]

Need to actually generate the .class files when building, since the src/main/test compilation needs the .class from src/main/java being present.

[datho7561]

@testforstephen if you have some time, I would appreciate if you could review this change. I don't fully understand why the .class files were being generated in a temporary folder instead of the expected folder. When I debugged the JavaBuilder running with ECJ, the .class files for the source files were generated and placed in target by the BatchImageBuilder.

[datho7561]

I ran the quick fix test suite from jdt.ui on this PR and this PR causes a bunch of errors. I'll look into fixing those. seems to be a fluke, the test suite is flaky

[testforstephen]

@testforstephen if you have some time, I would appreciate if you could review this change. I don't fully understand why the .class files were being generated in a temporary folder instead of the expected folder. When I debugged the JavaBuilder running with ECJ, the .class files for the source files were generated and placed in target by the BatchImageBuilder.

Javac generates .class files in a temporary folder because the JDT builder API expects the compiler to return class bytes rather than writing the files directly. To meet this requirement, we work around the javac implementation by generating .class files in a temporary directory first, then return the bytes of the temp class file to the ImageBuilder via the CompilationResult. Once the upstream ImageBuilder accepts the CompilationResult, we will delete the temp Javac class files. You can find the full discussion history in #535 (comment).

[testforstephen]

I tried lemminx project with Javac bits, it can generate classes and test-classes under target directory successfully. Could you clarify the specific issue you encountered that you intend to address with this PR?

[datho7561]

If you clean the project, (eg. delete all the .class files under target) and rebuild, then many of the test files won't be able to compile, since compiling them relies on referencing the compiled source files, which aren't generated when the compilation of the test files starts.

[testforstephen]

If you clean the project, (eg. delete all the .class files under target) and rebuild, then many of the test files won't be able to compile, since compiling them relies on referencing the compiled source files, which aren't generated when the compilation of the test files starts.

After deleting the target directory manually, I use "Force Java Compilation -> Full" command to perform a full build, it can regenerate all class files. In current implementation, we only persist class files for the requested ICompilationUnits in the compile operation. For those intermediate dependency sources, we don't persist class files for them. this is by design.

[datho7561]

Okay, I checked again, and compiling lemminx now works properly.

Some of the changes in this PR were related to compiling modules properly; I'll check if they are still necessary and move them over to a new PR.