[concept] Let PDE compute required packages using a CompilationParticipant

[laeubi]

There are some case where the JDT concept of classpath restrictions do not match well the OSGi runtime handling of imported packages these include:

• inlined constants are never visible at runtime and therefore no import required and no restriction issue
• indirect references through super types are handled by the classpath of the providing bundle and not the consumer
• methods inherited from superclasses are also not a problem at all

This is now a radical change in how PDE handles the case and detects problems:

• instead of using access restrictions that try to emulate the runtime behavior, it computes a full set of transitive classpath items and add them unrestricted (except for internal packages to get warnings there)
• then during compilation we dynamically compute the actual set of required imports at runtime
• if any of these imports are missing in the manifest we create a problem and suggest suitable quickfix

This has the benefit that we are in full control over what is detected, how it is reported and where it is reported. It also gives much more flexibility in improving user experience, for example one might even want to have some "autoimport" feature that is adding /removing packages on demand so do not bother the user with doing this daunting task manually.

This is currently a concept!

This means the PR description might not match fully the current implementation, it is likely not to be merged soon but allows discussion and exploring of possibilities of further enhancements what might then further refine the concept presented here or act as a reference to other improvements we need from the components we are using so answering the question "why" for new features and showing concrete code examples.

This would then require a similar change in Tycho, where we already do some preprocessing and handling based on class file analysis.

[github-actions]

Test Results

  618 files   -   147    618 suites   - 147   52m 57s ⏱️ - 1m 21s
3 611 tests ±    0  3 556 ✅  -     1   54 💤 ± 0  1 ❌ +1 
8 183 runs   - 2 651  8 043 ✅  - 2 628  139 💤  - 24  1 ❌ +1 

For more details on these failures, see this check.

Results for commit b178887. ± Comparison against base commit e7b608f.