server: add SlideX/Y constraint adjustment to popups

Allows popups that would normally go offscreen to stay visible. X11 doesn't seem
to like windows whose bounds go less than 0x0, so we adjust the position
reported to X11 to make it happy.

I am worried this will have some other implications with popups, but we'll see
what happens.

src/server/event.rs

@@ -227,8 +227,8 @@ impl SurfaceEvents {
             let (scale_factor, window, window_data) = query.get().unwrap();
 
             let window = *window;
-            let x = (pending.x as f64 * scale_factor.0) as i32 + window_data.output_offset.x;
-            let y = (pending.y as f64 * scale_factor.0) as i32 + window_data.output_offset.y;
+            let x = (pending.x.max(0) as f64 * scale_factor.0) as i32 + window_data.output_offset.x;
+            let y = (pending.y.max(0) as f64 * scale_factor.0) as i32 + window_data.output_offset.y;
             let width = if pending.width > 0 {
                 (pending.width as f64 * scale_factor.0) as u16
             } else {

src/server/mod.rs

@@ -25,6 +25,7 @@ use wayland_protocols::xdg::decoration::zv1::client::zxdg_decoration_manager_v1:
 use wayland_protocols::xdg::decoration::zv1::client::zxdg_toplevel_decoration_v1::{
     self, ZxdgToplevelDecorationV1,
 };
+use wayland_protocols::xdg::shell::client::xdg_positioner::ConstraintAdjustment;
 use wayland_protocols::{
     wp::{
         fractional_scale::v1::client::wp_fractional_scale_manager_v1::WpFractionalScaleManagerV1,
@@ -1407,6 +1408,8 @@ impl<S: X11Selection + 'static> InnerServerState<S> {
             (parent_window.attrs.dims.width as f64 / initial_scale) as i32,
             (parent_window.attrs.dims.height as f64 / initial_scale) as i32,
         );
+        positioner
+            .set_constraint_adjustment(ConstraintAdjustment::SlideX | ConstraintAdjustment::SlideY);
         let popup = xdg.get_popup(
             Some(&parent_role.xdg().unwrap().surface),
             &positioner,

testwl/src/lib.rs

@@ -1740,6 +1740,7 @@ impl Dispatch<XdgPositioner, ()> for State {
             xdg_positioner::Request::Destroy => {
                 data.remove();
             }
+            xdg_positioner::Request::SetConstraintAdjustment { .. } => {}
             other => todo!("unhandled positioner request {other:?}"),
         }
     }