Let a new window pick its own size instead of forcing a guessed placeholder

Root-caused "windows spawn small and square, not remembering placement or
size": new_managed_window hardcoded a fresh toplevel's geometry to 800x632
before the client had said anything about its own preferred size, and
sync_geometry forced that guess onto the client's very first
xdg_toplevel::configure unconditionally. Per xdg-shell, size: None on that
first configure is how every mainstream compositor lets a client pick its
own natural size instead; this one never did, so every app converged on
the same placeholder rectangle regardless of what it would have chosen.

Window::size_is_provisional marks a size that really was just the guess
(not a remembered geometry, a rule's explicit geometry action, or a
maximize/phone-mode fill, none of which are guesses). sync_geometry sends
size: None for such a window's first configure; a new adopt_provisional_size,
called from the commit handler, adopts the client's own real first size
into Window::geometry the moment it commits one, clamping only position so
a bigger-than-guessed window can't hang off its monitor's edge.

Live-verified in a nested compositor: a zenity dialog now renders at its
own compact natural size instead of being stretched to the old guess.

1 files changed, 7 insertions, 0 deletions

diff --git a/crates/wayland/src/protocols/compositor.rs b/crates/wayland/src/protocols/compositor.rs
index f7e7b74..e2868e4 100644
--- a/crates/wayland/src/protocols/compositor.rs
+++ b/crates/wayland/src/protocols/compositor.rs
@@ -83,6 +83,13 @@ impl CompositorHandler for CompState {
             if let Some(w) = self.id_to_window.get(&id) {
                 w.on_commit();
             }
+            // See `Window::size_is_provisional`'s own doc comment: before
+            // anything below reads `Window::geometry` (`redraw_decoration_
+            // buffer`, `sync_geometry`), give a window still waiting on its
+            // own first real size a chance to adopt it from what `on_commit`
+            // just recomputed, rather than keep rendering/configuring
+            // against the guessed placeholder for one more round-trip.
+            self.adopt_provisional_size(id);
             // See `content_epoch`'s doc comment: this is the only per-commit
             // signal the udev backend's rounded-corner mask cache has to
             // invalidate itself, since content can change every frame,