nixos/firejail: remove the need for qualifications

nixos/modules/programs/firejail.nix

@@ -8,18 +8,21 @@ let
   wrappedBins = pkgs.runCommand "firejail-wrapped-binaries"
     { preferLocalBuild = true;
       allowSubstitutes = false;
+      # take precedence over non-firejailed versions
+      meta.priority = -1;
     }
     ''
       mkdir -p $out/bin
+      mkdir -p $out/share/applications
       ${lib.concatStringsSep "\n" (lib.mapAttrsToList (command: value:
       let
         opts = if builtins.isAttrs value
         then value
-        else { executable = value; profile = null; extraArgs = []; };
+        else { executable = value; desktop = null; profile = null; extraArgs = []; };
         args = lib.escapeShellArgs (
           opts.extraArgs
           ++ (optional (opts.profile != null) "--profile=${toString opts.profile}")
-          );
+        );
       in
       ''
         cat <<_EOF >$out/bin/${command}
@@ -27,6 +30,11 @@ let
         exec /run/wrappers/bin/firejail ${args} -- ${toString opts.executable} "\$@"
         _EOF
         chmod 0755 $out/bin/${command}
+
+        ${lib.optionalString (opts.desktop != null) ''
+          substitute ${opts.desktop} $out/share/applications/$(basename ${opts.desktop}) \
+            --replace ${opts.executable} $out/bin/${command}
+        ''}
       '') cfg.wrappedBinaries)}
     '';
 
@@ -42,6 +50,12 @@ in {
             description = lib.mdDoc "Executable to run sandboxed";
             example = literalExpression ''"''${lib.getBin pkgs.firefox}/bin/firefox"'';
           };
+          desktop = mkOption {
+            type = types.nullOr types.path;
+            default = null;
+            description = lib.mkDoc ".desktop file to modify. Only necessary if it uses the absolute path to the executable.";
+            example = literalExpression ''"''${pkgs.firefox}/share/applications/firefox.desktop"'';
+          };
           profile = mkOption {
             type = types.nullOr types.path;
             default = null;
@@ -71,12 +85,6 @@ in {
       '';
       description = lib.mdDoc ''
         Wrap the binaries in firejail and place them in the global path.
-
-        You will get file collisions if you put the actual application binary in
-        the global environment (such as by adding the application package to
-        `environment.systemPackages`), and applications started via
-        .desktop files are not wrapped if they specify the absolute path to the
-        binary.
       '';
     };
   };