Redo: add doc to ghc wrapper

[matthewbauer]

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[peti]

Ignoring all file collisions in the ghc-wrapper feels like a hack. I'd rather not do this.

[matthewbauer]

I think that's due to buildEnv propagating the dependencies. Not sure how to turn that off. I'd actually prefer to set allowCollisions here regardless because that is what symlinkJoin does by default.

For instance, compare:

{ pkgs ? import <nixpkgs> {} }:

pkgs.symlinkJoin {
  name = "test";
  paths = [
    (pkgs.writeTextDir "/share/doc/uuid-types-1.0.3/html/uuid-types.haddock" "a")
    (pkgs.writeTextDir "/share/doc/uuid-types-1.0.3/html/uuid-types.haddock" "b")
  ];
}

vs.

{ pkgs ? import <nixpkgs> {} }:

pkgs.buildEnv {
  name = "test";
  paths = [
    (pkgs.writeTextDir "/share/doc/uuid-types-1.0.3/html/uuid-types.haddock" "a")
    (pkgs.writeTextDir "/share/doc/uuid-types-1.0.3/html/uuid-types.haddock" "b")
  ];
}

[peti]

I prefer to treat collisions as an error. Because they usually are.

[matthewbauer]

I'm not sure how to avoid the regression then. The two packages given in the revert (cabal-plan & aeson), depend on two different versions of uuid-types:

$ nix-store -qR $(nix-build '<nixpkgs>' -A haskellPackages.cabal-plan) | grep uuid-types
/nix/store/vs6xvan33d5jmhaybwkddmdfljigm050-uuid-types-1.0.3-doc
/nix/store/pv27lwjz900idmyrf0hykhfr95a2yk44-uuid-types-1.0.3
$ nix-store -qR $(nix-build '<nixpkgs>' -A haskellPackages.aeson) | grep uuid-types
/nix/store/s9babnwzfpq4vj02p20070pxfc6zpilx-uuid-types-1.0.3-doc
/nix/store/ciqb2va7qbhzb0b0s5ak289pnks3bfvd-uuid-types-1.0.3

We could just add map (lib.getOutput "doc") to the symlinkJoin, if that seems better.

[peti]

I am not sure how to remedy that issue. My problem with the "simple solution" is this: If different versions of a package exist, then these versions differ in the set of dependencies they link or flags they've been compiled with or something like that. Arguably, those differences may very well manifest in the API and in the generated documentation, so I would assume that those foobar.haddock files might differ, too. Ignoring collisions means that we'll just pick a random one and link it into the generated store path. But that doesn't feel right. The foobar.haddock file you'll get should be bundled in some obvious way with the library that it belongs to. This means that doc hierarchy might need $out baked into its directory name, maybe? Then there would be no more file collisions, because the *.haddock files would no longer be ambiguous. Does that make sense?

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[stale]

I marked this as stale due to inactivity. → More info