shell.nix with nimlsp

shell.nix

let
  # Assumes niv sources, which should include the repos for
  # nimlsp, ast-pattern-matching and jsonschema.
  sources = import ./nix/sources.nix;
  pkgs = import sources.nixpkgs {};

  unpackedSource = d: d.overrideAttrs (orig: {
    name = "${orig.pname}-source";
    phases = ["unpackPhase" "patchPhase" "installPhase"];
    installPhase = "mkdir $out; cp -aR . $out/.";
  });

  nimlsp = pkgs.stdenv.mkDerivation {
    name = "nimlsp";
    src = sources.nimlsp;
    buildInputs = [ pkgs.nim ];
    buildPhase = ''
      mkdir -p $TMPDIR/.nimcache
      mkdir -p $out/bin
      nim c --nimcache:$TMPDIR/.nimcache \
        -d:tempDir= \
        -d:explicitSourcePath:${unpackedSource pkgs.nim} \
        --path:${unpackedSource pkgs.nim}/nimsuggest \
        --path:${sources.nim-ast-pattern-matching}/src \
        --path:${sources.nim-jsonschema}/src \
        -o:$out/bin/nimlsp src/nimlsp
      rm -r $TMPDIR/.nimcache
   '';
    phases = ["unpackPhase" "buildPhase"];
  };
in
pkgs.mkShell {
  NIX_PATH = "nixpkgs=${sources.nixpkgs}";

  buildInputs = [
    pkgs.nixpkgs-fmt
    pkgs.niv
    pkgs.nim
    nimlsp
  ];
}