gdk/wayland: Implement toplevel tag protocol

The toplevel tag would an application developer to tag a toplevel
surface with a tag.

When combined with the application-id, the compositor can use that
information to identify specific windows and use it for
configurability/scriptability.

The protocol:
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/238

gdk/wayland/gdkdisplay-wayland.c

@@ -63,6 +63,7 @@
 #include "linux-dmabuf-unstable-v1-client-protocol.h"
 #include "presentation-time-client-protocol.h"
 #include "xx-color-management-v4-client-protocol.h"
+#include "xdg-toplevel-tag-v1-client-protocol.h"
 
 #include "wm-button-layout-translation.h"
 
@@ -554,6 +555,12 @@ gdk_registry_handle_global (void               *data,
         wl_registry_bind (display_wayland->wl_registry, id,
                           &xdg_system_bell_v1_interface, 1);
     }
+  else if (strcmp (interface, xdg_toplevel_tag_manager_v1_interface.name) == 0)
+    {
+      display_wayland->xdg_toplevel_tag =
+        wl_registry_bind (display_wayland->wl_registry, id,
+                          &xdg_toplevel_tag_manager_v1_interface, 1);
+    }
 
   g_hash_table_insert (display_wayland->known_globals,
                        GUINT_TO_POINTER (id), g_strdup (interface));
@@ -770,6 +777,7 @@ gdk_wayland_display_dispose (GObject *object)
   g_clear_pointer (&display_wayland->dmabuf_formats_info, dmabuf_formats_info_free);
   g_clear_pointer (&display_wayland->color, gdk_wayland_color_free);
   g_clear_pointer (&display_wayland->system_bell, xdg_system_bell_v1_destroy);
+  g_clear_pointer (&display_wayland->xdg_toplevel_tag, xdg_toplevel_tag_manager_v1_destroy);
 
   g_clear_pointer (&display_wayland->shm, wl_shm_destroy);
   g_clear_pointer (&display_wayland->wl_registry, wl_registry_destroy);

gdk/wayland/gdkdisplay-wayland.h

@@ -126,6 +126,7 @@ struct _GdkWaylandDisplay
   struct wp_viewporter *viewporter;
   struct wp_presentation *presentation;
   struct wp_single_pixel_buffer_manager_v1 *single_pixel_buffer;
+  struct xdg_toplevel_tag_manager_v1 *xdg_toplevel_tag;
   GdkWaylandColor *color;
 
   GList *async_roundtrips;

gdk/wayland/gdktoplevel-wayland.c

@@ -38,6 +38,7 @@
 #include <wayland/xdg-shell-unstable-v6-client-protocol.h>
 #include <wayland/xdg-foreign-unstable-v2-client-protocol.h>
 #include <wayland/xdg-dialog-v1-client-protocol.h>
+#include "xdg-toplevel-tag-v1-client-protocol.h"
 
 #include <stdlib.h>
 #include <stdio.h>
@@ -1257,7 +1258,7 @@ gdk_wayland_toplevel_set_transient_for (GdkWaylandToplevel *toplevel,
 
 #define LAST_PROP 1
 
-static void 
+static void
 gdk_wayland_toplevel_set_decorated (GdkWaylandToplevel *self,
                                     gboolean            decorated)
 {
@@ -2480,6 +2481,50 @@ gdk_wayland_toplevel_set_application_id (GdkToplevel *toplevel,
     }
 }
 
+
+/**
+ * gdk_wayland_toplevel_set_tag:
+ * @toplevel: (type GdkWaylandToplevel): a `GdkToplevel` to set the tag for
+ * @tag: A preferably human-readable tag
+ *
+ * Set a tag to the toplevel allowing to uniquely identify it from the compositor
+ * side.
+ *
+ * The tag along with the application ID can be used to create a unique identifier
+ * per app / window.
+ *
+ * The tag may be shown to the user in UI, so it's preferable for
+ * it to be human readable. Suitable tags would for example be
+ * “main window”, “settings”, “e-mail composer” or similar.
+ *
+ * The tag does not need to be unique across applications.
+
+ * Returns: whether the tag was set.
+ *
+ * Since: 4.18
+ */
+gboolean
+gdk_wayland_toplevel_set_tag (GdkToplevel *toplevel,
+                              const char  *tag)
+{
+  GdkWaylandToplevel *wayland_toplevel = GDK_WAYLAND_TOPLEVEL (toplevel);
+  GdkSurface *surface = GDK_SURFACE (toplevel);
+  GdkDisplay *display = gdk_surface_get_display (surface);
+  GdkWaylandDisplay *display_wayland = GDK_WAYLAND_DISPLAY (display);
+
+  if (!display_wayland->xdg_toplevel_tag)
+    {
+      g_warning ("Server is missing xdg_toplevel_tag support");
+      return FALSE;
+    }
+
+  xdg_toplevel_tag_manager_v1_set_toplevel_tag (display_wayland->xdg_toplevel_tag,
+                                                wayland_toplevel->display_server.xdg_toplevel,
+                                                tag);
+
+  return TRUE;
+}
+
 gboolean
 gdk_wayland_toplevel_inhibit_idle (GdkToplevel *toplevel)
 {

gdk/wayland/gdkwaylandtoplevel.h

@@ -67,4 +67,8 @@ GDK_AVAILABLE_IN_ALL
 void                     gdk_wayland_toplevel_set_application_id (GdkToplevel *toplevel,
                                                                   const char  *application_id);
 
+GDK_AVAILABLE_IN_4_18
+gboolean                 gdk_wayland_toplevel_set_tag            (GdkToplevel *toplevel,
+                                                                  const char  *tag);
+
 G_END_DECLS

gdk/wayland/meson.build

@@ -156,6 +156,11 @@ proto_sources = [
     'stability': 'private',
     'version': 1,
   },
+  {
+    'name': 'xdg-toplevel-tag',
+    'stability': 'private',
+    'version': 1,
+  },
 ]
 
 gdk_wayland_gen_headers = []

gdk/wayland/protocol/xdg-toplevel-tag-v1.xml

@@ -0,0 +1,70 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="xdg_toplevel_tag_v1">
+  <copyright>
+    Copyright © 2024 Xaver Hugl
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice (including the next
+    paragraph) shall be included in all copies or substantial portions of the
+    Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+  </copyright>
+
+  <interface name="xdg_toplevel_tag_manager_v1" version="1">
+    <description summary="protocol for setting toplevel tags">
+      In order to make some window properties like position, size, "always on top"
+      or user defined rules for window behavior persistent, the compositor needs
+      some way to identify windows even after the application has been restarted.
+      This protocol allows clients to make this possible by setting a tag for
+      toplevels.
+
+      Warning! The protocol described in this file is currently in the testing
+      phase. Backward compatible changes may be added together with the
+      corresponding interface version bump. Backward incompatible changes can
+      only be done by creating a new major version of the extension.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy toplevel tag object">
+        Destroy this toplevel tag factory object. This request has no other effects.
+      </description>
+    </request>
+
+    <enum name="error">
+      <entry name="tag_on_mapped" value="0"
+             summary="attempted to tag an already mapped toplevel"/>
+    </enum>
+
+    <request name="set_toplevel_tag">
+      <description summary="set tag">
+        Set a tag for a toplevel. The tag may be shown to the user in UI, so it's preferable for
+        it to be human readable. Suitable tags would for example be "main window", "settings",
+        "e-mail composer" or similar.
+
+        The tag does not need to be unique across applications, and the client may set the same
+        tag for multiple windows, for example if the user has opened the same UI twice.
+        How the potentially resulting conflicts are handled is compositor policy.
+
+        If a tag is set at all, the client must set the tag as part of the initial commit on the
+        associated toplevel. If the toplevel is already mapped, or the following wl_surface.commit
+        after this request maps the surface, the tag_on_mapped error is emitted.
+      </description>
+      <arg name="toplevel" type="object" interface="xdg_toplevel"/>
+      <arg name="tag" type="string"/>
+    </request>
+  </interface>
+
+</protocol>

gtk/inspector/general.c

@@ -743,6 +743,7 @@ add_wayland_protocols (GdkDisplay          *display,
       append_wayland_protocol_row (gen, (struct wl_proxy *)d->single_pixel_buffer);
       append_wayland_protocol_row (gen, d->color ? gdk_wayland_color_get_color_manager (d->color) : NULL);
       append_wayland_protocol_row (gen, (struct wl_proxy *)d->system_bell);
+      append_wayland_protocol_row (gen, (struct wl_proxy *)d->xdg_toplevel_tag);
     }
 }
 #endif