Is it easily possible to use nixpkgs GHC?

[L-as]

I remember reading that it used to be more similar to nixpkgs GHC or something along those lines.

[hamishmack]

I'm keen to try to get this working. It would be a nice for people to get up and running quickly without configuring the nix cache. They would still need to build a lot of packages if they did not configure a cache with haskell.nix stuff in it, but GHC would at least be built for them.

If you would like to give it a go, an overlay like this might be a good start for experimenting:

final: prev: {
  haskell-nix = prev.haskell-nix // {
    compiler = prev.haskell-nix.compiler // {
      ghc8107 = prev.haskell.compiler.ghc8107 // {
         # Add stuff not in nixpkgs ghc
         configured-src = prev.haskell-nix.compiler.ghc8107.configured-src; # Needed for reinstallableLibGhc to work
      };
    };
  };
}

If we get it working it would be nice to improve the way ghc is selected. Something that also worked for when we want to use a branch of ghc from git would be nice.

[michaelpj]

Another reason why this might be useful: at the moment when working on haskell.nix or nix-tools, it's easy to make a change that forces a rebuild of GHC, which is then very annoying to get through. If we could drop in a nixpkgs GHC, then we could iterate on haskell.nix and test out the building of some actual projects without having to rebuild GHC.

[shlevy]

See also #1531

[shlevy]

@L-as Did you ever try this overlay approach?

[L-as]

I have not unfortunately.

[ParetoOptimalDev]

I'm keen to try to get this working. It would be a nice for people to get up and running quickly without configuring the nix cache. They would still need to build a lot of packages if they did not configure a cache with haskell.nix stuff in it, but GHC would at least be built for them.

If you would like to give it a go, an overlay like this might be a good start for experimenting:

final: prev: {
  haskell-nix = prev.haskell-nix // {
    compiler = prev.haskell-nix.compiler // {
      ghc8107 = prev.haskell.compiler.ghc8107 // {
         # Add stuff not in nixpkgs ghc
         configured-src = prev.haskell-nix.compiler.ghc8107.configured-src; # Needed for reinstallableLibGhc to work
      };
    };
  };
}

If we get it working it would be nice to improve the way ghc is selected. Something that also worked for when we want to use a branch of ghc from git would be nice.

I had some time and was curious. This is what happens with the above:

error: It is likely you used `haskell.compiler.X` instead of `haskell-nix.compiler.X` for haskell-project

       … while evaluating anonymous lambda

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/lib/call-cabal-project-to-nix.nix:9:1:

            8| in
            9| { name          ? src.name or null # optional name for better error messages
             | ^
           10| , src

       … from call site

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/haskell.nix:464:36:

          463|             let
          464|               callProjectResults = callCabalProjectToNix args;
             |                                    ^
          465|               plan-pkgs = importAndFilterProject {

       … while realising the context of a path

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/lib/import-and-filter-project.nix:18:13:

           17|   projectSubDir'' = if projectSubDir == "" then "" else projectSubDir + "/"; # With trailing /
           18|   project = import "${projectNix}${projectSubDir'}";
             |             ^
           19| in project // {

       … while evaluating anonymous lambda

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/lib/import-and-filter-project.nix:5:1:

            4| { pkgs, haskellLib }:
            5| { projectNix, sourceRepos, src }:
             | ^
            6| let

       … from call site

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/haskell.nix:465:27:

          464|               callProjectResults = callCabalProjectToNix args;
          465|               plan-pkgs = importAndFilterProject {
             |                           ^
          466|                 inherit (callProjectResults) projectNix sourceRepos src;

       … while evaluating the attribute 'hsPkgs'

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/haskell.nix:495:43:

          494|               project = addProjectAndPackageAttrs rec {
          495|                   inherit (pkg-set.config) hsPkgs;
             |                                           ^
          496|                   inherit pkg-set;

       … while evaluating the attribute 'hsPkgs'

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/haskell.nix:525:15:

          524|               # Haskell packages
          525|               hsPkgs = final.lib.mapAttrs (packageName: package':
             |               ^
          526|                 if package' == null

       … while evaluating 'project'

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/haskell.nix:852:19:

          851|         # for `cabalPackage` and `stackPackage`.
          852|         project = args: let p = project' args;
             |                   ^
          853|           in p.hsPkgs // p;

       … from call site

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/hix.nix:38:8:

           37|       projectDefaults = importDefaults (toString (src.origSrcSubDir or src) + "/nix/hix.nix");
           38|     in final.haskell-nix.project [
             |        ^
           39|             (import ../modules/hix-project.nix)

       … while evaluating 'project'

       at /nix/store/mrdp8ykh0l1lkrylh92rs658060d1jj4-source/overlays/hix.nix:3:5:

            2|   project =
            3|     { src
             |     ^
            4|     , userDefaults ? {}

       … from call site

       at /nix/store/lyisa1dj0l6dcbhxhsmqcbkj6532wp1v-source/flake.nix:28:15:

           27|             hixProject =
           28|               final.haskell-nix.hix.project {
             |               ^
           29|                 src = ./.;

       … while evaluating the attribute 'hixProject.flake'

       at /nix/store/lyisa1dj0l6dcbhxhsmqcbkj6532wp1v-source/flake.nix:27:13:

           26|             };
           27|             hixProject =
             |             ^
           28|               final.haskell-nix.hix.project {

       … while evaluating anonymous lambda

       at /nix/store/lyisa1dj0l6dcbhxhsmqcbkj6532wp1v-source/flake.nix:15:52:

           14|     in
           15|       flake-utils.lib.eachSystem supportedSystems (system:
             |                                                    ^
           16|       let

       … from call site

       at /nix/store/0zdncmv2n5sncs0sdphvggc61ix1fpsm-source/default.nix:128:17:

          127|         let
          128|           ret = f system;
             |                 ^
          129|           op = attrs: key:

       … while evaluating 'op'

       at /nix/store/0zdncmv2n5sncs0sdphvggc61ix1fpsm-source/default.nix:126:19:

          125|       # Merge together the outputs for all systems.
          126|       op = attrs: system:
             |                   ^
          127|         let

       … from call site

       at /nix/store/0zdncmv2n5sncs0sdphvggc61ix1fpsm-source/default.nix:144:5:

          143|     in
          144|     builtins.foldl' op { } systems
             |     ^
          145|   ;

       … while evaluating 'eachSystem'

       at /nix/store/0zdncmv2n5sncs0sdphvggc61ix1fpsm-source/default.nix:98:25:

           97|   #
           98|   eachSystem = systems: f:
             |                         ^
           99|     let

       … from call site

       at /nix/store/lyisa1dj0l6dcbhxhsmqcbkj6532wp1v-source/flake.nix:15:7:

           14|     in
           15|       flake-utils.lib.eachSystem supportedSystems (system:
             |       ^
           16|       let

       … while evaluating 'outputs'

       at /nix/store/lyisa1dj0l6dcbhxhsmqcbkj6532wp1v-source/flake.nix:6:13:

            5|   inputs.flake-utils.url = "github:numtide/flake-utils";
            6|   outputs = { self, nixpkgs, flake-utils, haskellNix }:
             |             ^
            7|     let

       … from call site

       at «string»:45:21:

           44|
           45|           outputs = flake.outputs (inputs // { self = result; });
             |                     ^
           46|

       … while evaluating anonymous lambda

       at «string»:10:13:

            9|     builtins.mapAttrs
           10|       (key: node:
             |             ^
           11|         let

       … from call site

       … while evaluating anonymous lambda

       at «string»:2:23:

            1|
            2| lockFileStr: rootSrc: rootSubdir:
             |                       ^
            3|

       … from call site

Because of:

assert (if ghc'.isHaskellNixCompiler or false then true
    else throw ("It is likely you used `haskell.compiler.X` instead of `haskell-nix.compiler.X`"
      + forName));

I guess next step is using my own fork and rmoving that?

[hamishmack]

See #1854

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ocharles]

I think this is still worth keeping open