New functions for pkgs.haskell.lib

[deemp]

Project description

I'd like to propose a couple of functions that should simplify the setup of Haskell projects.
I'm not aware if they're already available anywhere.

• getHaskellPackagesDeps - provides a list of all packages from getCabalDeps of packages p1,p2,...pN minus packages p1, p2, ..., pN. This allows for developing local packages with other local packages as dependencies. Only non-local packages will be collected.

• ghcForPackages - uses the previous function to construct a ghc with packages. It's a ghc with dependencies for local packages provided via an override of haskell.packages.

• It may be useful to provide a wrapper for cabal that puts the ghc with packages on PATH of cabal. That's a way to avoid conflicts between ghc versions in a devshell like haskell-language-server provides its own GHC in a devshell #225895

[cdepillabout]

getHaskellPackagesDeps and ghcForPackages sort of sound related to shellFor. Maybe some of the internals of shellFor could be factored out into separate functions?

It may be useful to provide a wrapper for cabal that puts the ghc with packages on PATH of cabal

People have argued in the past that cabal-install should pull in GHC, since GHC is required for using cabal-install. The reason we haven't done this is because people often use cabal-install with different versions of GHC. Or even do something like getting GHC from their system package manager, and getting cabal-install from Nixpkgs.

Having some sort of wrapper around cabal-install that locks it to a specific GHC version seems like it might satisfy this request. But I don't really know how I feel about it.

[deemp]

What I didn't like in shellFor was that it created a shell. I got used to devshell and didn't find an elegant way to combine a shellFor and a devshell. The workaround was to make a cabalFor (let's call it so) for cabal-install with ghcWithPackages on PATH so that I could use a single cabalFor package in a devShell instead of shellFor or cabal-install + ghcWithPackages.

[cdepillabout]

What I didn't like in shellFor was that it created a shell.

That's why I suggested

Maybe some of the internals of shellFor could be factored out into separate functions?

If I remember correctly, the internals of shellFor basically do what you're requesting. Factoring them out seems like a reasonable path forward.

I got used to devshell and didn't find an elegant way to combine a shellFor and a devshell

I'm not sure what devshell is, but guessing from the name of the repo, it sounds like it might be a reasonable request to be able to pass a mkShell environment to devshell. Maybe it would make more sense to open up an issue on devshell?

[deemp]

Indeed, it is possible to pass all *inputs from a shellFor derivation to a mkShell via packagesFrom.