libsForQt5.qtcurve: fix build with Qt5.15

moved the initial qtcurve package to mkLibsForQt5 function
to decouple from Qt5 version

added an alias qtcurve -> libsForQt5.qtcurve for backward compatibility

add option to disable gtk2 support (still enabled by default)

pkgs/data/themes/qtcurve/default.nix

@@ -1,43 +1,47 @@
-{ stdenv, fetchFromGitHub, cmake, extra-cmake-modules, pkgconfig, mkDerivation
-, gtk2, qtbase, qtsvg, qtx11extras # Toolkit dependencies
+{ lib, fetchFromGitHub, cmake, extra-cmake-modules, pkgconfig, mkDerivation
+, gtk2Support ? true, gtk2
+, qtbase, qtsvg, qtx11extras # Toolkit dependencies
 , karchive, kconfig, kconfigwidgets, kio, frameworkintegration
 , kguiaddons, ki18n, kwindowsystem, kdelibs4support, kiconthemes
 , libpthreadstubs, pcre, libXdmcp, libX11, libXau # X11 dependencies
 , fetchpatch
 }:
 
-let
-  version = "1.9.1";
-in mkDerivation {
+mkDerivation rec {
   pname = "qtcurve";
-  inherit version;
+  version = "1.9.1";
   src = fetchFromGitHub {
     owner = "KDE";
     repo = "qtcurve";
     rev = version;
-    sha256 = "0sm1fza68mwl9cvid4h2lsyxq5svia86l5v9wqk268lmx16mbzsw";
+    sha256 = "XP9VTeiVIiMm5mkXapCKWxfcvaYCkhY3S5RXZNR3oWo=";
   };
 
+  enableParallelBuilding = true;
+
   patches = [
+    # Remove unnecessary constexpr, this is not allowed in C++14
     (fetchpatch {
       url = "https://github.com/KDE/qtcurve/commit/ee2228ea2f18ac5da9b434ee6089381df815aa94.patch";
       sha256 = "1vz5frsrsps93awn84gk8d7injrqfcyhc1rji6s0gsgsp5z9sl34";
     })
+    # Fix build with Qt5.15
+    (fetchpatch {
+      url = "https://github.com/KDE/qtcurve/commit/44e2a35ebb164dcab0bad1a9158b1219a3ff6504.patch";
+      sha256 = "5I2fTxKRJX0cJcyUvYHWZx369FKk6ti9Se7AfYmB9ek=";
+    })
   ];
 
-  enableParallelBuilding = true;
-
   nativeBuildInputs = [ cmake extra-cmake-modules pkgconfig ];
 
   buildInputs = [
-    gtk2
     qtbase qtsvg qtx11extras
     karchive kconfig kconfigwidgets kio kiconthemes kguiaddons ki18n
     kwindowsystem kdelibs4support frameworkintegration
     libpthreadstubs
     pcre
     libXdmcp libX11 libXau
-  ];
+  ] ++ lib.optional gtk2Support gtk2;
 
   preConfigure = ''
     for i in qt5/CMakeLists.txt qt5/config/CMakeLists.txt
@@ -52,7 +56,12 @@ in mkDerivation {
     patchShebangs tools/gen-version.sh
   '';
 
-  meta = with stdenv.lib; {
+  configureFlags = [
+    "-DENABLE_GTK2=${if gtk2Support then "ON" else "OFF"}"
+    "-DENABLE_QT4=OFF"
+  ];
+
+  meta = with lib; {
     homepage = "https://github.com/QtCurve/qtcurve";
     description = "Widget styles for Qt5/Plasma 5 and gtk2";
     platforms = platforms.linux;

pkgs/top-level/aliases.nix

@@ -475,6 +475,7 @@ mapAliases ({
   quake3game = ioquake3; # added 2016-01-14
   qvim = throw "qvim has been removed."; # added 2020-08-31
   qwt6 = libsForQt5.qwt;  # added 2015-12-19
+  qtcurve = libsForQt5.qtcurve;  # added 2020-11-07
   qtpfsgui = throw "qtpfsgui is now luminanceHDR"; # added 2019-06-26
   quaternion-git = throw "quaternion-git has been removed in favor of the stable version 'quaternion'"; # added 2020-04-09
   rdf4store = throw "rdf4store has been removed from nixpkgs."; # added 2019-12-21

pkgs/top-level/all-packages.nix

@@ -15380,6 +15380,8 @@ in
 
     grantlee = callPackage ../development/libraries/grantlee/5 { };
 
+    qtcurve = callPackage ../data/themes/qtcurve {};
+
     herqq = callPackage ../development/libraries/herqq { };
 
     kdb = callPackage ../development/libraries/kdb { };
@@ -19692,8 +19694,6 @@ in
 
   qogir-theme = callPackage ../data/themes/qogir { };
 
-  qtcurve = libsForQt514.callPackage ../data/themes/qtcurve {};
-
   redhat-official-fonts = callPackage ../data/fonts/redhat-official { };
 
   route159 = callPackage ../data/fonts/route159 { };