Epic: Simplify the structure of the core repo and factor out Epoch in its own repo

[cmnrd]

This epic specifies the new envisioned and simplified project structure as well as concrete incremental steps we can take towards this goal.

Overview

Our current is very bloated and it is hard for newcomers to find their way through the forest of packages and directories. This structure has been been mostly dictated by Xtext and Eclipse. However, since we are moving away from Eclipse as our primary development IDE and Epoch is only one of our supported LF IDEs, we should aim at freeing our core repository from the constraints and overhead that Eclipse imposes. The best way to do this, is to separate our "core" repository from Epoch. Ideally, we strip the lingua-franca repository from all unnecessary Eclipse dependencies and Eclipse related code. This should instead be hosted in a separte Epoch repository where lingua-franca is a submodule.

The Goal

• The lingua-franca repository should look something like this:

  lingua-franca/
  ├── bin/
  ├── lib/
  ├── src/
  ├── test/
  

  Of course we will need some additional files and directories for gradle and other meta files, but the idea is to have a single point of entry for the source code. All code that is needed for our command line tools and the language server, should be located within src/. This includes the contents of org.lflang, org.lflang.lfc, org.lflang.diagrams and org.lflang.lds. The primary build tool for this repository would be gradle and any IDE could be used for development
• The Epoch repository would look similar to the current lingua franca repository. Most notably, org.lflang would become a submodule and point to the lingua-franca repository. The primary build tool for this repository would be maven and Eclipse the main IDE for development.
• Since the restructuring will be a breaking change, we also want to use the opportunity to fix Eliminate large files from git history #1078 and Rename master to main #423. The goal is to clean our git history and push the cleaned history to a new main branch. This way we can keep the old master branch for legacy, but start developing on main in our freshly cleaned up repo.

Action Items

• Bundle the core functionality of LF in org.lflang
  • Move contents of org.lflang.lfc to a subpackage lfc within org.lflang #1421
  • Move contents of org.lflang.diagram to a subpackage diagram within org.lflang
  • Build language server with Gradle which depends on publication of KlighD package
  • Remove org.lflang.ldsbecause no longer needed
  • Remove "Eclipse switch" from mwe2 file in lingua-franca repo
  • Get rid of injection of Kotlin-based generators in LFGenerator #1800
• Move util/tracing to separate repository or to reactor-c #1491
• Move actions for building the RTI and other files referring to the RTI to reactor-c or to a standalone RTI repository (also see The RTI should be factored out in its own repository reactor-c#5)
  - [ ] Find Epoch specific code in the code-base and move it out of org.lflang.
  • This includes the EclipseErrorReporter, but also any code where we check the mode of operation (standlone vs epoch)
• Move all Epoch specific code to its own repository, which its own mwe2 file that toggles the "Eclipse switch"
• Apply the new structure to the lingua-franca repository and update the Gradle config accordingly. This includes:
  • Use a source code layout that follows Gradle/Maven conventions #1801
  • Cleanup the gradle files and support the assemble task #1514
• Eliminate large files from git history #1078
• Rename master to main #423
• Make lingua-franca a submodule of Epoch

Optional:

• Publication of some or all modules to Maven Central #937
  The planned restructuring poses an opportunity for publishing the core package of LF on Maven central.

[oowekyala]

I don't see this mentioned here, but I think it would be nice to move the runtime submodules out of src/lib. It's unconventional, the src directory should only contain sources that Gradle will compile. AFAIU they were placed there to be packed in the Jar archive, but that doesn't need to be. We can just tell gradle to use these directories as resource directories.

A more conventional structure would be to have this lib directory at the root of the repo.

[cmnrd]

Thanks for the remark. I made this now an explicit part of the action items.

[cmnrd]

Closing this as the major part of the work is complete and the remaining issues are kind of open-ended

[lhstrh]

Should we still rename master to main? It will break a lot of things...

[cmnrd]

I think we should. Mostly because half of our repos use main and it would be nice to get some consistency...

The issue currently has the 0.6.0 milestone assigned, but I wouldn't mind pushing it a bit further down the road.

[lhstrh]

OK, makes sense. I'd rather just bite the bullet honestly...so I'm OK with doing it as part of 0.6.0...