Allow specifying the GHC to be used for the cabal cradle

[alanz]

A standard idiom is cabal new-configure --with-compiler=ghc-8.8.2.

Given a hie.yaml file is intended to set up the local developer's intentions, we should be able to specify the GHC compiler version with a cabal cradle.

As a side-effect, this can help tooling like hie and its successors to choose an appropriate version to run.

[sureyeaah]

I would like to take this on. It seems like a relatively easy task. What do you think?

[fendor]

That sounds nice! However, designing a nice API doesnt sound as easy. Also, we got to think about #44 of which this could be an extension. In a different approach, we could use cabal-install-parsers in hie/ghcide/hls to find the ghc version automatically.
I am happy for PR's but would like to discuss design ideas such as modifications in hie.yaml as well as changes in the types before.

[sureyeaah]

Has there been any progress on #44 ?

[fendor]

I have been implementing a prototype but there is not much to show at the moment.
First step would be discussing an hie.yaml format for it and should it be a global option, per cradle, etc... A lot to discuss. If you have any ideas, you can write them in #44!

[fendor]

@alanz Would it be better if hie-bios honours the configuration in cabal.project, etc... or if it was possible to specify the ghc version in hie.yaml?

[jneira]

both? 😝
but i see the first one in cabal-parser/cabal-helper and the explicit one in hie-bios
We will have to link to cabal-parser/helper in hie-bios to get the first one, right?

[fendor]

Not sure if both is really nice. E.g. cabal configure -w ghc-8.6.4 but you specify a different ghc in hie.yaml?

[alanz]

Hmm, I have been mentally using a workflow where the cabal.project is under version control, and is "general", without specifying the GHC version. This simplifies things like CI.

Then when working with a particular GHC version you configure it to use that. And I guess the same effect comes from using cabal.project.local.

But I have had experiences where I am working on a project which I manually configured with one version of GHC (say ghc-8.8.2), and then hie-bios periodically reconfigures it with the "default" ghc, being 8.6.5. So you end up fighting with it.

[fendor]

Yes, and I think the most intuitive approach would be that hie-bios uses the correctly configured version from cabal.project.local. However, if it does that, a custom field in hie.yaml would be superfluous.

[jneira]

closing as duplicate in favor of #194 (As there is a technical discussion on how to accomplish and a linked pr)