Ghcide: Give the user a choice of implicit cradle if there is more than one

[pepeiborra]

I think this is great and I'm happy to merge it, but I have a couple of requests that can either be done in this PR of in follow-ups:

1. Inform the user that there is no cradle #788
2. Write the implicit cradle to disk
3. Give the user a choice if there are both stack and cabal project descriptors
4. Delete all the cradle files from ghcide and hls - no longer needed

_Originally posted by @pepeiborra in https://github.com/haskell/ghcide/pull/782#issuecomment-691618901_

[fendor]

Additionally, it would be nice to define a default selection. E.g., personally I always want to use cabal and don't want to be asked again and again what type of cradle I want to have generated.

[pepeiborra]

Rather than a selection feature, just write it to disk?

[fendor]

Yeah, that probably suffices, it is not that bad to select once per project what tool you want to use.

[jneira]

A init param and/or lsp client setting, --default-build-tool would be great for this and maybe could be used for other things

[pepeiborra]

Just keep things simple. Ask the user to pick Cabal or Stack, generate it and write it to disk. Zero configuration, fewer questions, hopefully less issues raised about it.

[pepeiborra]

In the cradle-less plan where the implicit cradle is always used by default, I can see how you need config in case there is more than one choice.
My preference would be for a 3-way option "Ask/Cabal/Stack" where Ask is the default value and the answer is recorded in the project file system (e.g. in vscode/settings.json but ideally somewhere more portable).

[alanz]

Would the question be asked by means of window/showMessageRequest?

I would suggest storing the answer in a file in the project root, called something explicit like hie-implicit-choice, and populated with some explanation of what it means.

[jneira]

The settings.json belongs to the lsp spec, right? Any client can send a didChangeConfiguration request with the json so emacs, vim, etc can use it.
So i would use it instead add more config files.