Drop ghc-api-compat from dependency closure

[fendor]

Requires re-structuring GHC API Compatibility.

We try to go with the latest GHC API and provide backwards compatible
functions for older GHC versions. The intention is that ghcide code is
written with the latest GHC API in mind, older GHC versions may have
inefficiencies in order to satisfy the newer API.

This way dropping support for older GHC versions is trivial (only delete
a couple of '#if ... #endif' and maybe update some imports), and ghcide
does suffer less from bit-rot. Additionally, we want to have the latest
and best GHC API, not some semi-outdated frankenstein.

The implementation adds a new Compat sub-hierarchy that defines
backwards compatible functions for the GHC API, where possible
higher-level abstractions.

The module hierarchy re-organisation of GHC is taken care of by
'Development.IDE.GHC.Compat.Core', which takes care of almost every
definition used by ghcide. If this becomes to unwieldy, it makes sense
to split it up into smaller logical pieces.

Design Decisions:

• In ghcide, no GHC API import is allowed except for GHC.
• Restrict usage of CPP to modules in Compat hierarchy as much as possible.
• Plugins are allowed to provide their Backwards Compat methods.
  • E.g. they may use CPP instead of ghcide's Compat modules.

TODOS:

• Proper GHC 9.2 support (blocked on Support GHC 9.2 facebookincubator/retrie#36)
• Plugins
• Stack build files
• Nix Build Files

Status:
With all supported plugins, HLS compiles for GHC 8.6.5 ... 9.0.1.

[jneira]

Incredible herculean work here, many many thanks. I hope you dont mind cause ive marked it as a draft (following the title) and chenge the title itself to note it adds ghc-9.2 support

[fendor]

@jneira this PR can be merged before GHC 9.2 support lands

[fendor]

This adds GHC 9.0 support for the splice, rename, call-hierarchy and refineImports plugins.

I don't guarantee that they work correctly, but they compile :)

[jneira]

@fendor will try to help with stack files asap

[jneira]

Solver error for ghc-9.0.1:

Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: hls-1.3.0.0 (user goal)
[__1] trying: hls:+refineimports
[__2] trying: hls-refine-imports-plugin-1.0.0.0 (dependency of hls
+refineimports)
[__3] next goal: hls-plugin-api (user goal)
[__3] rejecting: hls-plugin-api-1.2.0.1 (conflict: hls-refine-imports-plugin
=> hls-plugin-api^>=1.1)
[__3] rejecting: hls-plugin-api-1.1.0.2, hls-plugin-api-1.1.0.1,
hls-plugin-api-1.1.0.0, hls-plugin-api-1.0.0.0, hls-plugin-api-0.7.1.0,
hls-plugin-api-0.7.0.0, hls-plugin-api-0.6.0.0, hls-plugin-api-0.5.0.1,
hls-plugin-api-0.5.0.0, hls-plugin-api-0.4.1.0, hls-plugin-api-0.4.0.0
(constraint from user target requires ==1.2.0.1)
[__3] fail (backjumping, conflict set: hls-plugin-api,
hls-refine-imports-plugin)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: hls-plugin-api, hls,
hls-refine-imports-plugin, hls:refineimports
Try running with --minimize-conflict-set to improve the error message.

I think it will be fixed by 19e0681

[jneira]

I've started to work on stack.yaml's here: https://github.com/jneira/haskell-language-server/tree/ghc92

[jneira]

LGTM, thanks for this again

[anka-213]

Thanks for cleaning up the mess I caused/contributed to when adding GHC-9.0 support! ❤️

[fendor]

@anka-213 Thank you for your GHC 9.0 support contribution, without this would have been harder!
You patched so many dependencies, it is awesome!