WIP for cabal show-build-info

[fendor]

Use features from haskell/cabal#7478

Starts work on #269

[jneira]

I guess it is using (or it can use) the already merged haskell/cabal#7498

[georgefst]

I'm curious, with upstream support in Cabal seemingly now implemented, is there anything blocking this? There are a lot of issues in HLS which mention this as the solution.

[fendor]

Yeah, there are unfortunately a couple of open issues 😅 Also, #409 essentially implements proper multi-home unit support without show-build-info.

[georgefst]

But #409 doesn't solve the issue of the user having to manually load all the right components to prevent errors like haskell/haskell-language-server#1370. I thought the point of show-build-info was that it finally gives us the information we need in order to know which components to load.

[georgefst]

But #409 doesn't solve the issue of the user having to manually load all the right components to prevent errors like haskell/haskell-language-server#1370.

Or maybe it does? I just noticed from haskell/haskell-language-server#3738 that the latest HLS release doesn't incorporate those commits yet.

[fendor]

But #409 doesn't solve the issue of the user having to manually load all the right components to prevent errors like haskell/haskell-language-server#1370. I thought the point of show-build-info was that it finally gives us the information we need in order to know which components to load.

It does! Conceptually, cabal repl --enable-multi-repl computes all the components you need to load into ghci, invokes ghci via ghci @args.unitA.txt @args.unitB.txt and HLS simply looks at these args and sets up the session appropriately.
Currently, the only advantage seems to be that show-build-info uses a well-defined interface instead of the hacky cabal repl -w hie-bios-ghc solution.

[georgefst]

Aha, awesome! Well then, I very much look forward to HLS being released with the new hie-bios.

[fendor]

I currently don't intend to work on this and it should be superseded by #409