neovim: allow extra Lua packages

pkgs/applications/editors/neovim/default.nix

@@ -50,6 +50,8 @@ in
 
     dontFixCmake = true;
 
+    inherit lua;
+
     buildInputs = [
       gperf
       libtermkey

pkgs/applications/editors/neovim/tests.nix

@@ -132,4 +132,15 @@ rec {
     extraName = "-pathogen";
     configure.pathogen.pluginNames = [ "vim-nix" ];
   };
+
+  nvimWithLuaPackages = wrapNeovim2 "with-lua-packages" (makeNeovimConfig {
+    extraLuaPackages = ps: [ps.mpack];
+    customRC = ''
+      lua require("mpack")
+    '';
+  });
+
+  nvim_with_lua_packages = runTest nvimWithLuaPackages ''
+    ${nvimWithLuaPackages}/bin/nvim -n -i NONE --noplugin -es
+  '';
 })

pkgs/applications/editors/neovim/utils.nix

@@ -28,6 +28,8 @@ let
     , extraPython3Packages ? (_: [ ])
     , withNodeJs ? false
     , withRuby ? true
+    /* the function you would have passed to lua.withPackages */
+    , extraLuaPackages ? (_: [ ])
 
     # expects a list of plugin configuration
     # expects { plugin=far-vim; config = "let g:far#source='rg'"; optional = false; }
@@ -76,6 +78,8 @@ let
         ++ (extraPython3Packages ps)
         ++ (lib.concatMap (f: f ps) pluginPython3Packages));
 
+      lua = neovim-unwrapped.lua;
+      luaEnv = lua.withPackages(ps: extraLuaPackages ps);
 
       # Mapping a boolean argument to a key that tells us whether to add or not to
       # add to nvim's 'embedded rc' this:
@@ -110,6 +114,9 @@ let
           "--set" "GEM_HOME" "${rubyEnv}/${rubyEnv.ruby.gemPath}"
         ] ++ lib.optionals (binPath != "") [
           "--suffix" "PATH" ":" binPath
+        ] ++ lib.optionals (luaEnv != null) [
+          "--prefix" "LUA_PATH" ";" "${luaEnv}/share/lua/${lua.luaversion}/?.lua"
+          "--prefix" "LUA_CPATH" ";" "${luaEnv}/lib/lua/${lua.luaversion}/?.so"
         ];
 
 
@@ -123,6 +130,7 @@ let
       inherit neovimRcContent;
       inherit manifestRc;
       inherit python3Env;
+      inherit luaEnv;
       inherit withNodeJs;
     } // lib.optionalAttrs withRuby {
       inherit rubyEnv;
@@ -143,6 +151,8 @@ let
     , extraPythonPackages ? (_: [])
     /* the function you would have passed to python.withPackages */
     , withPython3 ? true,  extraPython3Packages ? (_: [])
+    /* the function you would have passed to lua.withPackages */
+    , extraLuaPackages ? (_: [])
     , withNodeJs ? false
     , withRuby ? true
     , vimAlias ? false
@@ -159,6 +169,7 @@ let
       res = makeNeovimConfig {
         inherit withPython3;
         extraPython3Packages = compatFun extraPython3Packages;
+        inherit extraLuaPackages;
         inherit withNodeJs withRuby viAlias vimAlias;
         inherit configure;
         inherit extraName;