bios cradle requires correct ghc in path or in cradle defn

[adamse]

We use the bios cradle to hook ghcide up to our build system, that same build system also manages the ghc installation.

It would be preferable if the bios program could tell hie-bios where to look for ghc (or give it the libdir directly) so we don't have to know the path to the compiler outside the buildsystem.

[fendor]

What interface do you imagine?
A nice extension could be to add a field to the bios cradle:

cradle:
  bios:
    program: ./flags.sh
    ghc-program: ./ghc.sh

[adamse]

Maybe the bios program can gain an extra output file, it seems preferable not to have more programs. I guess looking at how we figure out the ghc for stack and cabal could be fruitful too.