@normalcea

suggestion: whitespacing and logical separation of arguments

This is just up to your preference, but I personally don't see the reason to add a whitespace between the other arguments and the Qt components/custom logic. The reason being that it then becomes arbitrary in what is separated by whitespace and what isn't and derivation code should always be as uniform as possible.

Fixed

question: kdePackages usage

I'm not an authority on Qt packaging, but why is kdePackages used here and not simply just qt6 I didn't notice a difference on my end (I'm using GNOME so all old qt stuff gets funneled into xwayland anyway).

I used kdePackages mostly as a habit since it's a complete set that includes qt6Packages (which in turn then includes qt6). But since qt6 is more minimal I do agree it should be used instead.

Also added fex-qt5 as a Qt5 version e.g. for Plasma 5 users.

Issue (blocking): Qt5 software is deprecated

• https://github.com/NixOS/nixpkgs/blob/master/doc/release-notes/rl-2505.section.md#other-notable-changes-sec-nixpkgs-release-2505-notable-changes

Plasma 5 and Qt 5 based versions of associated software are deprecated in NixOS 25.05, and will be removed in NixOS 25.11. Users are encouraged to upgrade to Plasma 6.

Plasma 5 is not a target anymore, so the additional fex-qt5 cannot be included.

Issue: multiple distinct changes in one commit

There are changes here not related to qt within the single commit here, they should be split off into an additional commit within this PR.

Done :)

nitpick: Un-refactor by removing with usage.

diff --git a/pkgs/by-name/fe/fex/package.nix b/pkgs/by-name/fe/fex/package.nix
index d3b563f89ded..0fc032d220fb 100644
--- a/pkgs/by-name/fe/fex/package.nix
+++ b/pkgs/by-name/fe/fex/package.nix
@@ -68,13 +68,10 @@ llvmPackages.stdenv.mkDerivation (finalAttrs: {
     xxHash
     fmt
   ]
-  ++ lib.optionals withQt (
-    with qt6;
-    [
-      qtbase
-      qtdeclarative
-    ]
-  );
+  ++ lib.optionals withQt [
+    qt6.qtbase
+    qt6.qtdeclarative
+  ];

   cmakeFlags = [
     (lib.cmakeFeature "CMAKE_BUILD_TYPE" "Release")

Oh, needs conflicts resolving.

Done

Right, the wrapQtApp needs to be an optionalString. I can't fix it right now but will fix it in a few hours.

Done, confirmed both with and without Qt builds and runs tests fine now.

Added back vulkan-headers as vendored, as FEX tracks a specific commit it's compatible with (needed for library forwarding).