"With-packages" wrapper for GHC does not wrap Haddock

[mrkkrp]

Issue description

We use haskell.packages.ghc822.ghcWithPackages which allows to add some packages to GHC installation so they are always visible. This works with ghc, ghci, ghc-pkg, but does not work for haddock because it's not wrapped, and so non-built-in packages are not visible to it.

Steps to reproduce

Put the following in a file called haddock-not-wrapped.nix:

let nixpkgs = import <nixpkgs> {};
in

nixpkgs.buildEnv {
  name = "my-thing";
  paths = with nixpkgs; [
    (haskell.packages.ghc822.ghcWithPackages (p: with p; [
      base
      binary
      binary-orphans
    ]))
    bash
  ];
}

Then execute:

$ nix-env -if haddock-not-wrapped.nix
$ which haddock
/root/.nix-profile/bin/haddock
$ haddock --optghc -package --optghc base
$ echo $?
0
$ haddock --optghc -package --optghc binary-orphans
<command line>: cannot satisfy -package binary-orphans
    (use -v for more information)
$ echo $?
1

Technical details

Please run nix-shell -p nix-info --run "nix-info -m" and paste the
results.

 - system: `"x86_64-linux"`
 - host os: `Linux 4.15.8-1-ARCH, Alpine Linux, noversion`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 1.11.14`
 - channels(root): `"nixpkgs-18.03pre128481.1098c071e59"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixpkgs

[srhb]

The slightly unfortunately named ghcWithHoogle also wraps haddocks up nicely. However, from your test case, I'm really not sure what problem you're trying to alleviate exactly. Could you describe what you're trying to achieve?

[mrkkrp]

Well, haddock should be able to see these packages like other tools (ghc, ghc-pkg) do.

[srhb]

Oh, I see, the resulting haddock is just a symlink to the generic (ghc-8.2) haddock, which does not point its -B flag at the combined set from ghcWithPackages. I wonder how difficult that would be to fix...

[srhb]

Conceptually, I think it's something like this...

export gwh=$(nix-build --no-out-link -E 'with import <nixpkgs> {}; haskellPackages.ghcWithHoogle (hps: with hps; [ binary binary-orphans  ])')

$gwh/bin/haddock -B $gwh/lib/ghc-* --optghc -package --optghc binary-orphans
echo $?

and the haddock wrapper in $gwh could just have that -B as its default.

[srhb]

Looks like it might be as simple as adding haddock to the loop in https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/haskell-modules/with-packages-wrapper.nix#L64

Or at least something very similar that sets -B correctly.

[srhb]

@mrkkrp Does this fix your issue? :)

[srhb]

Please reopen if this is still a problem. :)