xdg-desktop-portal: Use custom variable for finding portals

x-d-p only looks for portal definitions in one of two places:
- datadir (which we cannot install anything to, since Nix packages are immutable)
- when `XDG_DESKTOP_PORTAL_DIR` environment variable is set, the path specified therein
  (meant for tests, disables looking for portal configuration anywhere else)

Let’s introduce our own `NIX_XDG_DESKTOP_PORTAL_DIR` environment variable
that will only control the portal definitions lookup.
We will not use it for searching for configuration
because it would require looking in the parent directory
and `XDG_CONFIG_DIRS` variable is sufficient for us.

nixos/modules/config/xdg/portal.nix

@@ -119,19 +119,12 @@ in
     let
       cfg = config.xdg.portal;
       packages = [ pkgs.xdg-desktop-portal ] ++ cfg.extraPortals;
-      configPackages = cfg.configPackages;
 
       joinedPortals = pkgs.buildEnv {
         name = "xdg-portals";
         paths = packages;
         pathsToLink = [ "/share/xdg-desktop-portal/portals" "/share/applications" ];
       };
-
-      joinedPortalConfigs = pkgs.buildEnv {
-        name = "xdg-portal-configs";
-        paths = configPackages;
-        pathsToLink = [ "/share/xdg-desktop-portal" ];
-      };
     in
     mkIf cfg.enable {
       warnings = lib.optional (cfg.configPackages == [ ] && cfg.config == { }) ''
@@ -158,17 +151,20 @@ in
       systemd.packages = packages;
 
       environment = {
-        # fixes screen sharing on plasmawayland on non-chromium apps by linking
-        # share/applications/*.desktop files
-        # see https://github.com/NixOS/nixpkgs/issues/145174
-        systemPackages = [ joinedPortals ];
-        pathsToLink = [ "/share/applications" ];
+        systemPackages = [
+          joinedPortals
+        ] ++ cfg.configPackages;
+        pathsToLink = [
+          # Upstream desktop environment portal configurations.
+          "/share/xdg-desktop-portal"
+          # .desktop files to register fallback icon and app name.
+          "/share/applications"
+        ];
 
         sessionVariables = {
           GTK_USE_PORTAL = mkIf cfg.gtkUsePortal "1";
           NIXOS_XDG_OPEN_USE_PORTAL = mkIf cfg.xdgOpenUsePortal "1";
-          XDG_DESKTOP_PORTAL_DIR = "${joinedPortals}/share/xdg-desktop-portal/portals";
-          NIXOS_XDG_DESKTOP_PORTAL_CONFIG_DIR = mkIf (cfg.configPackages != [ ]) "${joinedPortalConfigs}/share/xdg-desktop-portal";
+          NIX_XDG_DESKTOP_PORTAL_DIR = "${joinedPortals}/share/xdg-desktop-portal/portals";
         };
 
         etc = lib.concatMapAttrs

pkgs/development/libraries/xdg-desktop-portal/default.nix

@@ -54,11 +54,10 @@ stdenv.mkDerivation (finalAttrs: {
     # Allow installing installed tests to a separate output.
     ./installed-tests-path.patch
 
-    # `XDG_DESKTOP_PORTAL_DIR` originally was used for upstream tests. But we are making use
-    # of this in the NixOS module, this actually blocks any configs from being loaded since
-    # configs are not expected to be placed in a portal implementation or even under the
-    # `share/xdg-desktop-portal/portals/` path.
-    ./separate-env-for-portal-config.patch
+    # Look for portal definitions under path from `NIX_XDG_DESKTOP_PORTAL_DIR` environment variable.
+    # While upstream has `XDG_DESKTOP_PORTAL_DIR`, it is meant for tests and actually blocks
+    # any configs from being loaded from anywhere else.
+    ./nix-pkgdatadir-env.patch
   ];
 
   nativeBuildInputs = [

pkgs/development/libraries/xdg-desktop-portal/nix-pkgdatadir-env.patch

@@ -0,0 +1,13 @@
+diff --git a/src/portal-impl.c b/src/portal-impl.c
+index 85b3a23..6d43636 100644
+--- a/src/portal-impl.c
++++ b/src/portal-impl.c
+@@ -275,6 +275,8 @@ load_installed_portals (gboolean opt_verbose)
+ 
+   /* We need to override this in the tests */
+   portal_dir = g_getenv ("XDG_DESKTOP_PORTAL_DIR");
++  if (portal_dir == NULL)
++    portal_dir = g_getenv ("NIX_XDG_DESKTOP_PORTAL_DIR");
+   if (portal_dir == NULL)
+     portal_dir = DATADIR "/xdg-desktop-portal/portals";
+ 

pkgs/development/libraries/xdg-desktop-portal/separate-env-for-portal-config.patch

@@ -1,33 +0,0 @@
-diff --git a/src/portal-impl.c b/src/portal-impl.c
-index 0fa9682e..99f379dc 100644
---- a/src/portal-impl.c
-+++ b/src/portal-impl.c
-@@ -433,8 +433,7 @@ load_portal_configuration (gboolean opt_verbose)
- 
-   desktops = get_current_lowercase_desktops ();
- 
--  /* We need to override this in the tests */
--  portal_dir = g_getenv ("XDG_DESKTOP_PORTAL_DIR");
-+  portal_dir = g_getenv ("NIXOS_XDG_DESKTOP_PORTAL_CONFIG_DIR_OVERRIDE");
- 
-   if (portal_dir != NULL)
-     {
-@@ -464,6 +463,18 @@ load_portal_configuration (gboolean opt_verbose)
-   if (load_config_directory (SYSCONFDIR "/" XDP_SUBDIR, desktops, opt_verbose))
-     return;
- 
-+  portal_dir = g_getenv ("NIXOS_XDG_DESKTOP_PORTAL_CONFIG_DIR");
-+
-+  if (portal_dir == NULL)
-+    /* We need to override this in the tests */
-+    portal_dir = g_getenv ("XDG_DESKTOP_PORTAL_DIR");
-+
-+  if (portal_dir != NULL)
-+    {
-+      if (load_config_directory (portal_dir, desktops, opt_verbose))
-+        return;
-+    }
-+
-   /* $XDG_DATA_HOME/xdg-desktop-portal/(DESKTOP-)portals.conf
-    * (just for consistency with other XDG specifications) */
-   g_clear_pointer (&user_portal_dir, g_free);