neovim-qt: wrap in separate derivation

This makes it possible to swap out the (wrapped) neovim without
recompiling neovim-qt. In particular, the user can use `neovim.override`
to configure their neovim and then use that same configuration for
neovim-qt, without having to give up binary caching.

pkgs/applications/editors/neovim/qt.nix

@@ -1,8 +1,9 @@
 { stdenv, fetchFromGitHub, cmake, doxygen, makeWrapper
 , msgpack, neovim, pythonPackages, qtbase }:
 
-stdenv.mkDerivation rec {
-  name = "neovim-qt-${version}";
+let
+  unwrapped = stdenv.mkDerivation rec {
+    pname = "neovim-qt-unwrapped";
     version = "0.2.11";
 
     src = fetchFromGitHub {
@@ -16,42 +17,25 @@ stdenv.mkDerivation rec {
       "-DUSE_SYSTEM_MSGPACK=1"
     ];
 
-  buildInputs = with pythonPackages; [
-    neovim qtbase msgpack
+    buildInputs = [
+      neovim.unwrapped # only used to generate help tags at build time
+      qtbase
     ] ++ (with pythonPackages; [
-    jinja2 msgpack python
+      jinja2 python msgpack
     ]);
 
     nativeBuildInputs = [ cmake doxygen makeWrapper ];
 
     enableParallelBuilding = true;
 
-  preConfigure = ''
-    # we rip out a number of tests that fail in the build env
-    # the GUI tests will never work but the others should - they did before neovim 0.2.0
-    # was released
-    sed -i test/CMakeLists.txt \
-      -e '/^add_xtest_gui/d' \
-      -e '/tst_neovimobject/d' \
-      -e '/tst_neovimconnector/d' \
-      -e '/tst_callallmethods/d' \
-      -e '/tst_encoding/d'
+    preCheck = ''
+      # The GUI tests require a running X server, disable them
+      sed -i ../test/CMakeLists.txt \
+        -e '/^add_xtest_gui/d'
     '';
 
     doCheck = true;
 
-  postInstall = if stdenv.isDarwin then ''
-    mkdir -p $out/Applications
-    mv $out/bin/nvim-qt.app $out/Applications
-    rmdir $out/bin || :
-
-    wrapProgram "$out/Applications/nvim-qt.app/Contents/MacOS/nvim-qt" \
-      --prefix PATH : "${neovim}/bin"
-  '' else ''
-    wrapProgram "$out/bin/nvim-qt" \
-      --prefix PATH : "${neovim}/bin"
-  '';
-
     meta = with stdenv.lib; {
       description = "Neovim client library and GUI, in Qt5";
       license     = licenses.isc;
@@ -59,4 +43,32 @@ stdenv.mkDerivation rec {
       inherit (neovim.meta) platforms;
       inherit version;
     };
-}
+  };
+in
+  stdenv.mkDerivation {
+    pname = "neovim-qt";
+    version = unwrapped.version;
+    buildCommand = if stdenv.isDarwin then ''
+      mkdir -p $out/Applications
+      cp -r ${unwrapped}/bin/nvim-qt.app $out/Applications
+
+      chmod -R a+w "$out/Applications/nvim-qt.app/Contents/MacOS"
+      wrapProgram "$out/Applications/nvim-qt.app/Contents/MacOS/nvim-qt" \
+        --prefix PATH : "${neovim}/bin"
+    '' else ''
+      makeWrapper '${unwrapped}/bin/nvim-qt' "$out/bin/nvim-qt" \
+        --prefix PATH : "${neovim}/bin"
+    '';
+
+    preferLocalBuild = true;
+
+    nativeBuildInputs = [
+      makeWrapper
+    ];
+
+    passthru = {
+      inherit unwrapped;
+    };
+
+    inherit (unwrapped) meta;
+  }