qt55.qtbase: build QGtkStyle by default

pkgs/development/libraries/qt-5/5.5/qtbase/default.nix

@@ -8,7 +8,7 @@
 , zlib, libjpeg, libpng, libtiff, sqlite, icu
 
 , coreutils, bison, flex, gdb, gperf, lndir, ruby
-, python, perl, pkgconfig
+, patchelf, perl, pkgconfig, python
 
 # optional dependencies
 , cups ? null
@@ -19,7 +19,7 @@
 , buildExamples ? false
 , buildTests ? false
 , developerBuild ? false
-, gtkStyle ? false, libgnomeui, GConf, gnome_vfs, gtk
+, gtkStyle ? true, libgnomeui, GConf, gnome_vfs, gtk
 , decryptSslTraffic ? false
 }:
 
@@ -27,6 +27,9 @@ let
   inherit (srcs.qt5) version;
   system-x86_64 = lib.elem stdenv.system lib.platforms.x86_64;
 
+  # Search path for Gtk plugin
+  gtkLibPath = lib.makeLibraryPath [ gtk.out gnome_vfs.out libgnomeui.out GConf.out ];
+
   dontInvalidateBacking = fetchurl {
     url = "https://codereview.qt-project.org/gitweb?p=qt/qtbase.git;a=patch;h=0f68f8920573cdce1729a285a92ac8582df32841;hp=24c50f8dcf7fa61ac3c3d4d6295c259a104a2b8c";
     name = "qtbug-48321-dont-invalidate-backing-store.patch";
@@ -43,7 +46,7 @@ stdenv.mkDerivation {
 
   sourceRoot = "qt-everywhere-opensource-src-${version}";
 
-  outputs = [ "dev" "out" ];
+  outputs = [ "dev" "out" "gtk" ];
 
   postUnpack = ''
     mv qtbase-opensource-src-${version} ./qt-everywhere-opensource-src-${version}/qtbase
@@ -51,7 +54,6 @@ stdenv.mkDerivation {
 
   patches =
     copyPathsToStore (lib.readPathsFromFile ./. ./series)
-    ++ lib.optional gtkStyle ./dlopen-gtkstyle.patch
     ++ lib.optional decryptSslTraffic ./decrypt-ssl-traffic.patch
     ++ lib.optional mesaSupported [ ./dlopen-gl.patch ./mkspecs-libgl.patch ];
 
@@ -89,14 +91,6 @@ stdenv.mkDerivation {
         qtbase/src/plugins/platforminputcontexts/compose/generator/qtablegenerator.cpp \
         --replace "@libX11@" "${libX11.out}"
     ''
-    + lib.optionalString gtkStyle ''
-      substituteInPlace qtbase/src/widgets/styles/qgtk2painter.cpp --replace "@gtk@" "${gtk.out}"
-      substituteInPlace qtbase/src/widgets/styles/qgtkstyle_p.cpp \
-        --replace "@gtk@" "${gtk.out}" \
-        --replace "@gnome_vfs@" "${gnome_vfs.out}" \
-        --replace "@libgnomeui@" "${libgnomeui.out}" \
-        --replace "@gconf@" "${GConf.out}"
-    ''
     + lib.optionalString mesaSupported ''
       substituteInPlace \
         qtbase/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp \
@@ -106,6 +100,7 @@ stdenv.mkDerivation {
         --replace "@mesa_inc@" "${mesa.dev}"
     '';
 
+
   setOutputFlags = false;
   preConfigure = ''
     export LD_LIBRARY_PATH="$PWD/qtbase/lib:$PWD/qtbase/plugins/platforms:$LD_LIBRARY_PATH"
@@ -217,7 +212,7 @@ stdenv.mkDerivation {
     ++ lib.optional (postgresql != null) postgresql
     ++ lib.optionals gtkStyle [gnome_vfs.out libgnomeui.out gtk GConf];
 
-  nativeBuildInputs = [ fixQtModuleCMakeConfig lndir python perl pkgconfig ];
+  nativeBuildInputs = [ fixQtModuleCMakeConfig lndir patchelf perl pkgconfig python ];
 
   # freetype-2.5.4 changed signedness of some struct fields
   NIX_CFLAGS_COMPILE = "-Wno-error=sign-compare";
@@ -243,6 +238,22 @@ stdenv.mkDerivation {
             done
         popd
     fi
+
+    # Move the QGtkStyle plugin to the gtk output
+    mkdir -p "$gtk/lib/qt5/plugins/platformthemes"
+    mv "$out/lib/qt5/plugins/platformthemes/libqgtk2.so" "$gtk/lib/qt5/plugins/platformthemes"
+    rm "$out/lib/cmake/Qt5Gui/Qt5Gui_QGtk2ThemePlugin.cmake"
+
+    # Set RPATH for QGtkStyle plugin
+    qgtk2="$gtk/lib/qt5/plugins/platformthemes/libqgtk2.so"
+    qgtk2_RPATH="$(patchelf --print-rpath "$qgtk2")"
+    qgtk2_RPATH="$qgtk2_RPATH''${qgtk2_RPATH:+:}${gtkLibPath}"
+    patchelf "$qgtk2" \
+        --add-needed libgtk-x11-2.0.so \
+        --add-needed libgnomeui-2.so \
+        --add-needed libgnomevfs-2.so \
+        --add-needed libgconf-2.so \
+        --set-rpath "$qgtk2_RPATH"
   '';
 
   postFixup =