Remove handling of ghc-x.y hls executables

[jneira]

(from a question in irc by arrowsvc)

• In several places the code is assuming a hls version compiled with ghc-x.y should (or could) work with all ghc-x.y.z runtime versions
  • hls-wrapper tries to use hls-x.y.z, hls-x.y and hls inthat order
  • the install script copies an hls version as hls-x.y
  • that assumption was inherited from hie but i think it worked in hls at some point (???)
• But you cant use that version with ghcide: ghcide compiled against GHC x.y.z but currently using x.y.w ...

So we should either make it work (again?) or remove its existence, cause it causes confusion
/cc @pepeiborra

[pepeiborra]

I don't think that we can guarantee compatibility across ghc versions, so my vote is for removing the handling too

[jneira]

That is unfortunate, i was planning cover all supported ghc versions with only 3 executables when setting up the chocolatey package for hls, but download all the minor verisons is a no go 😢

[ndmitchell]

@jneira - how would that work? Don't the minor variations between different GHC versions cause everything to go incompatible? Or, asked another way, what are the guarantees required to use a GHC 8.6.4 binary with 8.6.5, and could we get GHC HQ to commit to them?

[jneira]

It worked for haskell-ide-engine (hls inherited the code handling ghc-x.y from it), and i thought it did it for hls at some point, but surely i am wrong and never did it.
So i guess hie relied in the fact that if ghc patch version supposes no changes in the external api, nor error messages format or other info extracted you can handle an older ghc at runtime with a a version compiled against a newer one.

So the answer to

what are the guarantees required to use a GHC 8.6.4 binary with 8.6.5, and could we get GHC HQ to commit to them?

would be "no one, for the general case", so the safer option is require the exact version.

I am implementing another strategy for the choco package, assuming the fix to this issue will be to remove the handling of minor versions.