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haskell-nix.extraPkgconfigMappings documentation #1670

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19 changes: 18 additions & 1 deletion docs/tutorials/pkg-map.md
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Expand Up @@ -29,6 +29,23 @@ nixpkgs.overlays = [
];
```

The user can map package(s) in Nixpkgs to a `pkgconfig-depends` name by
overlaying the `haskell-nix.extraPkgconfigMappings` attribute:
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re: @yvan-sraka

Should we document that directly on the https://input-output-hk.github.io/haskell.nix/ manual?

I added this to the "Nixpkgs overlay" section of this tutorial since it also uses overlays. I guess it's more specifically a haskell-nix overlay, but still 🤔


```nix
nixpkgs.overlays = [
(self: super: {
haskell-nix = super.haskell-nix // {
extraPkgconfigMappings = super.haskell-nix.extraPkgconfigMappings // {
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You have to take care to not clobber other overlays that add mappings.

I have some helpers in my Nix code since this gets tedious:

{
    # See https://stackoverflow.com/a/54505212
    recursiveMerge = x: y: recursiveMergeAll [x y];
    recursiveMergeAll = attrList:
      with super.lib;
      let f = attrPath:
            zipAttrsWith (n: values:
              if tail values == []
              then head values
              else if all isList values
              then unique (concatLists values)
              else if all isAttrs values
              then f (attrPath ++ [n]) values
              else last values
            );
      in f [] attrList;

    mapExtraPkgconfig = super-haskell-nix: name: mappings: recursiveMerge super-haskell-nix {
      extraPkgconfigMappings = { "${name}" = mappings; };
    };
}

So my extraPkgconfigMappings overlays end up looking like this:

self: super:
{
  haskell-nix = super.macaroniLib.mapExtraPkgconfig super.haskell-nix "freeglut" ["freeglut"];
}

# String pkgconfig-depends names are mapped to lists of Nixpkgs
# package names
"SDL_gpu" = [ "SDL_gpu" ];
};
};
})
];
```

### Replace libraries of components

If a component is missing a dependency it can be added via modules. For example:
Expand Down Expand Up @@ -59,7 +76,7 @@ the Haskell.nix sources, so that it's solved for all users.
— for `build-tool-depends`, `frameworks`, `extra-libraries`, etc.

Each name can be mapped to:
1. A single package from nixkpgs.
1. A single package from nixpkgs.
2. `null` — eliminates the dependency
3. A list of packages — sometimes needed for dependencies such as `X11`.

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2 changes: 1 addition & 1 deletion overlays/haskell.nix
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Expand Up @@ -11,7 +11,7 @@ final: prev: {
# overlays.
defaultModules = [];

# TODO: doc etc
# Additional user-provided mappings to augment ./../lib/pkgconf-nixpkgs-map.nix
extraPkgconfigMappings = {};
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re: @L-as

This should probably be part of the project-common module.

What did you mean by this? I'm not familiar with the whole structure of haskell.nix, but would that also make it easy to set these options globally?

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@ramirez7 Sorry for the late response, yeah, essentially you add an option for it in modules/project-common.nix, then it's in the result of evaluating the module (see cabalProject') .

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    extraPkgconfigMappings = mkOption {
      type = submodule [ fill this out ];
      default = {};
      description = ''
        Extra pkgconfig mappings
      '';
    };

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hm I'll try this in a branch and get a good comparison going

# Nix Flake based source pins.
# To update all inputs, get unstable Nix and then `nix flake update --recreate-lock-file`
Expand Down