Confirm Nemo's popup works; fix the two bugs that hid it, and shadow bleed across a monitor seam

Nemo's right-click context menu was the last open punch-list item, parked
twice as untestable. It works: verified end to end in a throwaway nested
compositor, menu and submenu both, at the correct position and stacking.
The popup path itself needed no fix, so the POPUP-GEOM-DIAG/POPUP-GRAB-DIAG
diagnostics are removed.

Two real bugs turned up in the way of testing it.

zwlr_virtual_pointer was a silent no-op on the winit backend. Every
Motion/MotionAbsolute handler read UdevState::bounds() behind an early
return when state.udev was None, and that field is Some only for the DRM
backend. The protocol advertised its global, accepted create_virtual_pointer
and accepted every request, then discarded all motion with no error and no
log. That is the backend a nested instance runs on, so the only safe way to
drive a throwaway compositor - a Wayland client of that compositor, which
cannot reach any other session, unlike ydotool's /dev/uinput writes - did
not work at all. Bounds now come from WindowManager::monitors() when udev is
absent; both backends fill that list from Platform::monitors().

The winit backend's screencopy pass rendered no popups and no shadows. It
re-renders the scene offscreen, and that second scene was missing tiers, so
grim on a nested instance reported the opposite of the truth: a menu drawing
perfectly on screen photographed as absent. The DRM backend never had this,
since it serves screencopy from the on-screen frame it just drew. Border
strips are still missing from that pass, called out in the code rather than
left silent.

Also fixed, from the "windows show a bit in the other monitor" report:
shadow_rect expanded by SHADOW_SIZE on every side with no monitor-boundary
awareness, so a window flush against a seam put its 24px shadow strip on the
neighbouring screen. shadow_rect_clipped clips to the bounding box of the
monitors the window's geometry actually touches - not just its assigned
one, since a window straddling a seam really does occupy both and clipping
there would cut its shadow off mid-body. The bitmap's own extent stays
unclipped, because the src rectangle indexes into it; only the fragment list
is clipped. Six tests on the incident's own numbers. Not confirmed on
screen: the nested backend cannot produce a second monitor.

New tool: tools/virtual-pointer-click, a scriptable virtual-pointer driver
that acknowledges each command after its round-trip, so a test script can
put a screenshot between a move and the click that follows it.

489 tests pass, clippy clean.

1 files changed, 3 insertions, 25 deletions

diff --git a/crates/wayland/src/protocols/xdg_shell.rs b/crates/wayland/src/protocols/xdg_shell.rs
index 4fe0f6f..0236736 100644
--- a/crates/wayland/src/protocols/xdg_shell.rs
+++ b/crates/wayland/src/protocols/xdg_shell.rs
@@ -8,7 +8,6 @@ use smithay::input::pointer::Focus;
 use smithay::reexports::wayland_protocols::xdg::shell::server::xdg_toplevel;
 use smithay::reexports::wayland_server::protocol::wl_output::WlOutput;
 use smithay::reexports::wayland_server::protocol::wl_seat;
-use smithay::reexports::wayland_server::Resource;
 use smithay::utils::Serial;
 use smithay::wayland::shell::xdg::{PopupSurface, PositionerState, ToplevelSurface, XdgShellHandler, XdgShellState};
 
@@ -185,22 +184,11 @@ impl XdgShellHandler for CompState {
     /// real follow-up, not this fix); an occasional popup placed near a
     /// screen edge may render partly off it, which is cosmetic, not a hang.
     fn new_popup(&mut self, surface: PopupSurface, positioner: PositionerState) {
-        // Temporary: live report is that Nemo's right-click context menu
-        // never appears at all (not mispositioned - entirely invisible),
-        // while the exact same xdg_popup mechanism works for Firefox. Logs
-        // the unconstrained geometry this popup gets so a live repro tells
-        // us whether it's landing off-screen/degenerate (the known gap this
-        // function's own doc comment already flags) or something else
-        // entirely. Remove once resolved.
-        let geom = positioner.get_geometry();
-        let parent = surface.get_parent_surface();
-        log::warn!("POPUP-GEOM-DIAG geometry={geom:?} parent={:?}", parent.as_ref().map(|s| s.id()));
         surface.with_pending_state(|state| {
-            state.geometry = geom;
+            state.geometry = positioner.get_geometry();
             state.positioner = positioner;
         });
         if surface.send_configure().is_err() {
-            log::warn!("POPUP-GEOM-DIAG send_configure failed");
             return;
         }
         let _ = self.popups.track_popup(smithay::desktop::PopupKind::Xdg(surface));
@@ -223,19 +211,9 @@ impl XdgShellHandler for CompState {
     /// `resize_request` already ignore the same parameter.
     fn grab(&mut self, surface: PopupSurface, _seat: wl_seat::WlSeat, serial: Serial) {
         let popup = PopupKind::Xdg(surface);
-        let Ok(root) = find_popup_root_surface(&popup) else {
-            log::warn!("POPUP-GRAB-DIAG find_popup_root_surface failed");
-            return;
-        };
+        let Ok(root) = find_popup_root_surface(&popup) else { return };
         let seat = self.seat.clone();
-        let grab = match self.popups.grab_popup(root, popup, &seat, serial) {
-            Ok(g) => g,
-            Err(e) => {
-                log::warn!("POPUP-GRAB-DIAG grab_popup failed: {e:?}");
-                return;
-            }
-        };
-        log::warn!("POPUP-GRAB-DIAG grab established, has_pointer={} has_keyboard={}", seat.get_pointer().is_some(), seat.get_keyboard().is_some());
+        let Ok(grab) = self.popups.grab_popup(root, popup, &seat, serial) else { return };
         if let Some(keyboard) = seat.get_keyboard() {
             keyboard.set_grab(self, PopupKeyboardGrab::new(&grab), serial);
         }