refactor EclipseCollectionsCodeGenerator

[sullis]

This PR refactors EclipseCollectionsCodeGenerator and adds a new unit test (EclipseCollectionsCodeGeneratorTest).

EclipseCollectionsCodeGeneratorTest validates the generated Java source files for:

• api
• impl
• test

Classgraph library

This PR uses the classgraph library to load resources from the classpath.

When I started this PR, I tried casting the system class loader to URLClassLoader. This approach worked on Java 8 but did not work on later versions of Java.

Reference: https://stackoverflow.com/questions/54618721/migration-to-java11-classcastexception

skipBoolean flag

As I was writing the unit test, I learned that some of the STG templates do not produce valid Java code. I observed that "boolean" is not handled by the templates. I added the skipBoolean flag to these templates:

skipBoolean() ::= "true"

[motlin]

I wasn't familiar with the ClassGraph library before. I like how using it makes it possible to delete so much code from FileUtils. To me, it seems like introducing ClassGraph is the essence of this change. In addition, there are more changes to production code and templates. However, the PR and commit message only mentions adding unit tests.

[sullis]

I wasn't familiar with the ClassGraph library before. I like how using it makes it possible to delete so much code from FileUtils. To me, it seems like introducing ClassGraph is the essence of this change. In addition, there are more changes to production code and templates. However, the PR and commit message only mentions adding unit tests.

I have updated the PR title, PR description, and commit message. The description now contains a better explanation of my work.

[motlin]

~EclipseCollectionsCodeGenerator.generate() delegates to EclipseCollectionsCodeGenerator.sourceFileExists(outputFile) before rendering a file. So if a hand-written boolean version exists, we won't generate code for the template anyway.~

I read the test and now understand why you have this. The test just attempts to generate everything. It executes in the code generator module, so we're not even up to compiling the hand-written files yet.

[motlin]

My overall impression is that I like Classgraph and how it helps reduce code. I'm not sure about the test because it's going to run slowly and doesn't seem like it will catch much that the build doesn't already catch. And then there are some refactorings that are only necessary to support the test. I'm curious if anyone else wants to weigh in @donraab @prathasirisha etc

[donraab]

@motlin @sullis I think it makes sense to break this into separate PRs. The skipBoolean change looks straightforward and we should review that separately. If this means we are removing currently generated classes/interfaces then we'll have to think about this, but since 12.0 is a major release I don't have as many concerns about this. On the Classgraph front, looks like it should be ok, but would ask @nikhilnanivadekar if he thinks this will need Eclipse Foundation approval. It's a build time dependency only, and MIT license, so should be ok I think.