add: xdg-portal home-manager module

modules/home-manager/default.nix

@@ -1,4 +1,5 @@
 {
   fonts = import ./fonts.nix;
   monitors = import ./monitors.nix;
+  xdg-portal = import ./xdg-portal.nix;
 }

modules/home-manager/xdg-portal.nix

@@ -0,0 +1,164 @@
+{ config, pkgs, lib, ... }:
+
+let
+  inherit (lib)
+    mapAttrsToList mkEnableOption mkIf mkMerge mkOption optional optionalString
+    types;
+
+  associationOptions = with types;
+    attrsOf (coercedTo (either (listOf str) str)
+      (x: lib.concatStringsSep ";" (lib.toList x)) str);
+
+in {
+  meta.maintainers = [ lib.maintainers.misterio77 ];
+
+  options.xdg.portal = {
+    enable = mkEnableOption (lib.mdDoc
+      "[xdg desktop integration](https://github.com/flatpak/xdg-desktop-portal)")
+      // {
+        default = false;
+      };
+
+    extraPortals = mkOption {
+      type = types.listOf types.package;
+      default = [ ];
+      description = lib.mdDoc ''
+        List of additional portals to add to path. Portals allow interaction
+        with system, like choosing files or taking screenshots. At minimum,
+        a desktop portal implementation should be listed. GNOME and KDE already
+        adds `xdg-desktop-portal-gtk`; and
+        `xdg-desktop-portal-kde` respectively. On other desktop
+        environments you probably want to add them yourself.
+      '';
+    };
+
+    gtkUsePortal = mkOption {
+      type = types.bool;
+      visible = false;
+      default = false;
+      description = lib.mdDoc ''
+        Sets environment variable `GTK_USE_PORTAL` to `1`.
+        This will force GTK-based programs ran outside Flatpak to respect and use XDG Desktop Portals
+        for features like file chooser but it is an unsupported hack that can easily break things.
+        Defaults to `false` to respect its opt-in nature.
+      '';
+    };
+
+    xdgOpenUsePortal = mkOption {
+      type = types.bool;
+      default = false;
+      description = lib.mdDoc ''
+        Sets environment variable `NIXOS_XDG_OPEN_USE_PORTAL` to `1`
+        This will make `xdg-open` use the portal to open programs, which resolves bugs involving
+        programs opening inside FHS envs or with unexpected env vars set from wrappers.
+        See [#160923](https://github.com/NixOS/nixpkgs/issues/160923) for more info.
+      '';
+    };
+
+    config = mkOption {
+      type = types.attrsOf associationOptions;
+      default = { };
+      example = {
+        x-cinnamon = { default = [ "xapp" "gtk" ]; };
+        pantheon = {
+          default = [ "pantheon" "gtk" ];
+          "org.freedesktop.impl.portal.Secret" = [ "gnome-keyring" ];
+        };
+        common = { default = [ "gtk" ]; };
+      };
+      description = lib.mdDoc ''
+        Sets which portal backend should be used to provide the implementation
+        for the requested interface. For details check {manpage}`portals.conf(5)`.
+
+        Configs will be linked to `/etx/xdg/xdg-desktop-portal/` with the name `$desktop-portals.conf`
+        for `xdg.portal.config.$desktop` and `portals.conf` for `xdg.portal.config.common`
+        as an exception.
+      '';
+    };
+
+    configPackages = mkOption {
+      type = types.listOf types.package;
+      default = [ ];
+      example = lib.literalExpression "[ pkgs.gnome.gnome-session ]";
+      description = lib.mdDoc ''
+        List of packages that provide XDG desktop portal configuration, usually in
+        the form of `share/xdg-desktop-portal/$desktop-portals.conf`.
+
+        Note that configs in `xdg.portal.config` will be preferred if set.
+      '';
+    };
+  };
+
+  config = let
+    cfg = config.xdg.portal;
+
+    joinedPortals = pkgs.buildEnv {
+      name = "xdg-portals";
+      paths = cfg.extraPortals;
+      pathsToLink =
+        [ "/share/xdg-desktop-portal/portals" "/share/applications" ];
+    };
+
+    portalConfigPath = n:
+      "share/xdg-desktop-portal/${
+        optionalString (n != "common") "${n}-"
+      }portals.conf";
+    mkPortalConfig = desktop: conf:
+      pkgs.writeTextDir (portalConfigPath desktop)
+      (lib.generators.toINI { } { preferred = conf; });
+
+    joinedPortalConfigs = pkgs.buildEnv {
+      name = "xdg-portal-configs";
+      ignoreCollisions = true; # Let config override configPackages cfgs
+      paths = (mapAttrsToList mkPortalConfig cfg.config) ++ cfg.configPackages;
+      pathsToLink = [ "/share/xdg-desktop-portal" ];
+    };
+  in mkIf cfg.enable (mkMerge [
+    {
+      warnings = optional (cfg.configPackages == [ ] && cfg.config == { }) ''
+        xdg-desktop-portal 1.17 reworked how portal implementations are loaded, you
+        should either set `xdg.portal.config` or `xdg.portal.configPackages`
+        to specify which portal backend to use for the requested interface.
+
+        https://github.com/flatpak/xdg-desktop-portal/blob/1.18.1/doc/portals.conf.rst.in
+
+        If you simply want to keep the behaviour in < 1.17, which uses the first
+        portal implementation found in lexicographical order, use the following:
+
+        xdg.portal.config.common.default = "*";
+      '';
+
+      assertions = [{
+        assertion = cfg.extraPortals != [ ];
+        message =
+          "Setting xdg.portal.enable to true requires a portal implementation in xdg.portal.extraPortals such as xdg-desktop-portal-gtk or xdg-desktop-portal-kde.";
+      }];
+
+      # Make extraPortals systemd units available to the user
+      home.packages = [ pkgs.xdg-desktop-portal ] ++ cfg.extraPortals;
+
+      systemd.user.services.xdg-desktop-portal = {
+        Unit = {
+          Description = "Portal service";
+          PartOf = "graphical-session.target";
+        };
+        Service = {
+          Environment = [
+            "XDG_DESKTOP_PORTAL_DIR=${joinedPortals}/share/xdg-desktop-portal/portals"
+          ] ++ (optional (cfg.configPackages != [ ])
+            "NIXOS_XDG_DESKTOP_PORTAL_CONFIG_DIR=${joinedPortalConfigs}/share/xdg-desktop-portal");
+          Type = "dbus";
+          BusName = "org.freedesktop-portal.Desktop";
+          ExecStart = "${pkgs.xdg-desktop-portal}/libexec/xdg-desktop-portal";
+          Slice = "session.slice";
+        };
+      };
+    }
+    # This module uses mkMerge because HM's home.sessionVariables are (at the
+    # time of writing) scalars, which do not work with mkIf
+    (mkIf cfg.gtkUsePortal { home.sessionVariables.GTK_USE_PORTAL = "1"; })
+    (mkIf cfg.xdgOpenUsePortal {
+      home.sessionVariables.NIXOS_XDG_OPEN_USE_PORTAL = "1";
+    })
+  ]);
+}