Multi component support

[alanz]

This is something that is in hie, but not yet in ghcide, and is critical to encouraging existing hie users to switch over.

[alanz]

The work is happening here haskell/ghcide#361

[jneira]

Mmm maybe i am wrong but afaiu in hie it was solved via cabal-helper, it has its own caveats but maybe it could be a better solution (see haskell/ghcide#361 (comment))
could be added to ghcide itself? now that cabal-helper has a no copyleft license... 🤔

[ndmitchell]

My understanding is cabal helper is quite complex. What's the mechanism by which it solves multi components?

[cocreature]

As far as I know cabal-helper does not solve multi components. What it does is to give you a list of multiple components and their flags. You still have to figure out what to do with those flags. So in that sense, it is like an implicit hie-bios multi-cradle.

[fendor]

Afaik, multi-components are solved via multiple HscEnvs (so, afaict very similar to the approach in haskell/ghcide#361). CabalHelper does nothing except for finding the build-flags given a filepath. In fact, cabal-helper is only used in Cradle.hs.

[jneira]

Oh so i misunderstood it, sorry for the noise. cabal-helper only help (he) in make hie.yaml optional, true.

[alanz]

I had a crazy shower thought this morning. What if we run a separate sub-ghcid per component? As a full blown process.

[cocreature]

Separate processes are even more wasteful than a separate HscEnv per component. The only upside is that you avoid issues like the global RTS linker but I don’t expect that to actually cause issues within things that are intended to be built together (as opposed to completely unrelated packages) and it’s already no longer global in GHC 8.10.

[alanz]

Ok, that makes sense. As I said, it was an off-the-wall thought. My preference is a single executable.

[alanz]

See also https://github.com/digital-asset/ghcide/issues/113

[alanz]

And I understand @mpickering is now working on this.

[maksbotan]

Hi. Seeing that today you released something, I finally decided to check this project out, with the hope that it would solve my problems related to TH.

However, in a multi-component project (several different cabal packages with one cabal.project) with correctly configured hie.yaml I am seeing this strange behavior:

[typecheck] [E] ROOT/code/morley-ledgers/src/Lorentz/Contracts/ManagedLedger/Doc.hs:27:16: error:
    Ambiguous occurrence ‘Markdown’
    It could refer to
       either ‘Lorentz.Markdown’,
              imported from ‘Lorentz’ at ROOT/code/morley-ledgers/src/Lorentz/Contracts/ManagedLedger/Doc.hs:21:1-14
              (and originally defined in ‘Util.Markdown’)
           or ‘Util.Markdown.Markdown’,
              imported from ‘Util.Markdown’ at ROOT/code/morley-ledgers/src/Lorentz/Contracts/ManagedLedger/Doc.hs:25:1-20
              (and originally defined
                 at ROOT/code/morley/src/Util/Markdown.hs:32:1-23)

As you can see, in this file I have Markdown coming from two different imports (Lorentz and Util.Markdown), but the first one is just a re-export of the second, so there is in fact only one type.

How can I help you debug this further?

[mpickering]

@maksbotan I think this is a known bug where if you load multiple components you sometimes end up with incompatible interface files. Try deleting ~/.cache/ghcide

[maksbotan]

Okay, after cleaning cache and loading only that file it does not fail. I'll try to use hls and if this happens again I'll report.
Thanks!