Consider including .mix directory into buildMix output

[lukateras]

Reported by @goodsoft. It seems that unless .mix is persisted, Dialyzer cannot be used during check phase. Which would mean it has to be preserved in the output.

One way to do it could be:

{ pkgs ? import ./pkgs.nix {} }: with pkgs;

let
  inherit (callPackage ./. {}) mixToNix;

  exposeDotMix = drv: drv.overrideAttrs (super: {
    postInstall = ''
      mv .mix $out || true
    '';
  });
in

mixToNix {
  src = ./tests/01-poison;
  overlay = final: lib.mapAttrs (lib.const exposeDotMix);
}

[lukateras]

@goodsoft wrote on Apr 18, 2019 7:19pm UTC:

The ultimate list of things required to make Mix work correctly with Hex-based dependencies:

1. deps/<name>/.hex file
2. _build/$MIX_ENV/lib/<name>/.mix directory
3. Hex.SCM instead of Mix.SCM.Path in _build/$MIX_ENV/lib/<name>/.mix/compile.elixir_scm file, which is :erlang.term_to_binary/1-encoded

Note that mix-bootstrap used by buildMix puts dependencies in the hardcoded location only for prod environment.

Currently I use the following workaround:

 fixHexDep = drv: drv.overrideAttrs (super: {
   postInstall = ''
     MIXDIR="_build/$MIXENV/lib/${drv.pname}/.mix"
     OUTDIR="$out/lib/erlang/lib"

     [ -e .hex ] && {
       ${elixir}/bin/elixir -e ":ok = :file.write_file(\"$MIXDIR/compile.elixir_scm\", \"$MIXDIR/compile.elixir_scm\" |> :file.read_file() |> elem(1) |> :erlang.binary_to_term() |> put_elem(2, Hex.SCM) |> :erlang.term_to_binary())"
       cp -Hrt "$OUTDIR/${super.name}/" "$MIXDIR" .hex
     } || true
   '';
 });

 (mixToNix {
   src = gitIgnore ./. [];
   overlay = final: lib.mapAttrs (lib.const fixHexDep);
 }).overrideAttrs (super: {
   postConfigure = ''
     mkdir -p _build/test/lib deps
     cp -Rv _build/prod/lib/* _build/test/lib/
     cp -Rv _build/prod/lib/* deps/
   '';
 });

By the way, with this --no-deps-check is not needed for any mix command anymore, as its checks succeed.