nixos/{budgie,cinnamon,mate}: Hack around SSH_AUTH_SOCK

Make sure SSH_AUTH_SOCK is known by these sessions, which are not
systemd managed. It should not be a problem for users who know this
environment variable and use multiple desktops environments to
opt-out of this and I would prefer a more out-of-the-box experience
for those who don't.

nixos/modules/services/x11/desktop-managers/budgie.nix

@@ -130,7 +130,8 @@ in
 
     services.xserver.desktopManager.budgie.sessionPath = [ pkgs.budgie-desktop-view ];
 
-    environment.extraInit = ''
+    environment.extraInit =
+      ''
         ${concatMapStrings (p: ''
           if [ -d "${p}/share/gsettings-schemas/${p.name}" ]; then
             export XDG_DATA_DIRS=$XDG_DATA_DIRS''${XDG_DATA_DIRS:+:}${p}/share/gsettings-schemas/${p.name}
@@ -140,6 +141,13 @@ in
             export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}${p}/lib
           fi
         '') cfg.sessionPath}
+      ''
+      + lib.optionalString config.services.gnome.gcr-ssh-agent.enable ''
+        # Hack: https://bugzilla.redhat.com/show_bug.cgi?id=2250704 still
+        # applies to sessions not managed by systemd.
+        if [ -z "$SSH_AUTH_SOCK" ] && [ -n "$XDG_RUNTIME_DIR" ]; then
+          export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/gcr/ssh"
+        fi
       '';
 
     environment.systemPackages =

nixos/modules/services/x11/desktop-managers/cinnamon.nix

@@ -87,7 +87,8 @@ in
       };
 
       # Have to take care of GDM + Cinnamon on Wayland users
-      environment.extraInit = ''
+      environment.extraInit =
+        ''
           ${concatMapStrings (p: ''
             if [ -d "${p}/share/gsettings-schemas/${p.name}" ]; then
               export XDG_DATA_DIRS=$XDG_DATA_DIRS''${XDG_DATA_DIRS:+:}${p}/share/gsettings-schemas/${p.name}
@@ -98,6 +99,13 @@ in
               export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}${p}/lib
             fi
           '') cfg.sessionPath}
+        ''
+        + lib.optionalString config.services.gnome.gcr-ssh-agent.enable ''
+          # Hack: https://bugzilla.redhat.com/show_bug.cgi?id=2250704 still
+          # applies to sessions not managed by systemd.
+          if [ -z "$SSH_AUTH_SOCK" ] && [ -n "$XDG_RUNTIME_DIR" ]; then
+            export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/gcr/ssh"
+          fi
         '';
 
       # Default services

nixos/modules/services/x11/desktop-managers/mate.nix

@@ -59,6 +59,14 @@ in
         pkgs.mate.mate-session-manager
       ];
 
+      environment.extraInit = lib.optionalString config.services.gnome.gcr-ssh-agent.enable ''
+        # Hack: https://bugzilla.redhat.com/show_bug.cgi?id=2250704 still
+        # applies to sessions not managed by systemd.
+        if [ -z "$SSH_AUTH_SOCK" ] && [ -n "$XDG_RUNTIME_DIR" ]; then
+          export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/gcr/ssh"
+        fi
+      '';
+
       # Debugging
       environment.sessionVariables.MATE_SESSION_DEBUG = mkIf cfg.debug "1";