[mutter/gnome-3-38] wayland/xdg-shell: Imitate undefined behavior Qt relies upon

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 067af969c03c31a2b7380b14f3344ef7d2258313
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Nov 12 14:06:43 2020 +0100

    wayland/xdg-shell: Imitate undefined behavior Qt relies upon
    
    Qt sets window geometry without in the same commit providing actual
    content matching it, and relies on the compositor being able to adapt
    without a new window geometry on a later commit. Other compositors do
    this, so do the same, even though it's not guaranteed according to spec.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1557
    (cherry picked from commit f5b44be9f22efd59b34dd8c3a98328306f979eea)
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1559

 src/wayland/meta-wayland-xdg-shell.c | 13 +++++++++++--
 src/wayland/meta-window-wayland.c    |  9 ++++++++-
 2 files changed, 19 insertions(+), 3 deletions(-)
---
diff --git a/src/wayland/meta-wayland-xdg-shell.c b/src/wayland/meta-wayland-xdg-shell.c
index 176f8a908f..43505932dc 100644
--- a/src/wayland/meta-wayland-xdg-shell.c
+++ b/src/wayland/meta-wayland-xdg-shell.c
@@ -89,6 +89,7 @@ typedef struct _MetaWaylandXdgSurfacePrivate
   struct wl_resource *resource;
   MetaWaylandXdgShellClient *shell_client;
   MetaRectangle geometry;
+  MetaRectangle unconstrained_geometry;
 
   guint configure_sent : 1;
   guint first_buffer_attached : 1;
@@ -810,7 +811,7 @@ meta_wayland_xdg_toplevel_post_apply_state (MetaWaylandSurfaceRole  *surface_rol
     META_WAYLAND_SURFACE_ROLE_CLASS (meta_wayland_xdg_toplevel_parent_class);
   surface_role_class->post_apply_state (surface_role, pending);
 
-  if (!pending->newly_attached)
+  if (!surface->buffer_ref->buffer)
     return;
 
   window_geometry = meta_wayland_xdg_surface_get_window_geometry (xdg_surface);
@@ -1536,6 +1537,7 @@ meta_wayland_xdg_surface_real_reset (MetaWaylandXdgSurface *xdg_surface)
   priv->first_buffer_attached = FALSE;
   priv->configure_sent = FALSE;
   priv->geometry = (MetaRectangle) { 0 };
+  priv->unconstrained_geometry = (MetaRectangle) { 0 };
   priv->has_set_geometry = FALSE;
 }
 
@@ -1578,12 +1580,19 @@ meta_wayland_xdg_surface_post_apply_state (MetaWaylandSurfaceRole  *surface_role
 
   if (pending->has_new_geometry)
     {
+      priv->unconstrained_geometry = pending->new_geometry;
       meta_wayland_shell_surface_determine_geometry (shell_surface,
                                                      &pending->new_geometry,
                                                      &priv->geometry);
       priv->has_set_geometry = TRUE;
     }
-  else if (!priv->has_set_geometry)
+  else if (priv->has_set_geometry)
+    {
+      meta_wayland_shell_surface_determine_geometry (shell_surface,
+                                                     &priv->unconstrained_geometry,
+                                                     &priv->geometry);
+    }
+  else
     {
       MetaRectangle new_geometry = { 0 };
 
diff --git a/src/wayland/meta-window-wayland.c b/src/wayland/meta-window-wayland.c
index 4ddecb4327..89ee0c292c 100644
--- a/src/wayland/meta-window-wayland.c
+++ b/src/wayland/meta-window-wayland.c
@@ -999,7 +999,14 @@ meta_window_wayland_finish_move_resize (MetaWindow              *window,
   else
     {
       if (acked_configuration)
-        calculate_offset (acked_configuration, &new_geom, &rect);
+        {
+          calculate_offset (acked_configuration, &new_geom, &rect);
+        }
+      else
+        {
+          rect.x = window->rect.x;
+          rect.y = window->rect.y;
+        }
     }
 
   if (rect.x != window->rect.x || rect.y != window->rect.y)