buildLuarocksPackage: save luarocks config as derivation (#269402)

* buildLuarocksPackage: save luarocks config as derivation

while debugging luarocks packages, it's exhausting to have to build
them, look at what random folder they've been built to finally look for
their config.


With this you can run
    nix build lua51Packages.plenary-nvim.configFile -f . 

and infer what luarocks will do.

* Update pkgs/development/interpreters/lua-5/build-luarocks-package.nix

Co-authored-by: Marc Jakobi <mrcjkb89@outlook.com>

---------

Co-authored-by: Marc Jakobi <mrcjkb89@outlook.com>

pkgs/development/interpreters/lua-5/build-luarocks-package.nix

@@ -3,6 +3,7 @@
 , lua
 , wrapLua
 , luarocks
+, writeTextFile
 
 # Whether the derivation provides a lua module or not.
 , luarocksCheckHook
@@ -83,7 +84,7 @@ let
 
   __structuredAttrs = true;
   env = {
-    LUAROCKS_CONFIG="$PWD/${luarocks_config}";
+    LUAROCKS_CONFIG = self.configFile;
   } // attrs.env or {};
 
   generatedRockspecFilename = "${rockspecDir}/${pname}-${rockspecVersion}.rockspec";
@@ -111,6 +112,12 @@ let
   # explicitly inherit this for it to be available as a shell variable in the
   # builder
   rocksSubdir = "${self.pname}-${self.version}-rocks";
+
+  configFile = writeTextFile {
+    name = pname + "-luarocks-config.lua";
+    text = self.luarocks_content;
+  };
+
   luarocks_content = let
       externalDepsGenerated = lib.filter (drv: !drv ? luaModule)
         (self.nativeBuildInputs ++ self.propagatedBuildInputs ++ self.buildInputs);
@@ -131,12 +138,6 @@ let
 
   configurePhase = ''
     runHook preConfigure
-
-    cat > ${luarocks_config} <<EOF
-    ${self.luarocks_content}
-    EOF
-    export LUAROCKS_CONFIG="$PWD/${luarocks_config}";
-    cat "$LUAROCKS_CONFIG"
   ''
   + lib.optionalString (self.rockspecFilename == null) ''
     rockspecFilename="${self.generatedRockspecFilename}"