script/compositor: Send mouseleave events when cursor moves between <iframe>s (#38539)

Properly send `mouseleave` events when the cursor moves between
`<iframe>`s. This allows a better handling of cursor changes and status
text updates. Specifically, we do not need to continuously update the
cursor and the value can be cached in the `Document`. In addition,
status updates can now be sent properly when moving focus between
`<iframe>`s.

Note that style updates for `:hover` values are still broken, but less
so than before. Now the hover state on the `Node` is updated, but for
some
reason the restyle isn't taking place properly. This maintains the
status quo as far as behavior goes when hover moves between `<iframe>`s.

This change also adds a helper data structure to `Document` which will
eventually be responsible for event handling.

Testing: Cursor and status change are currently very hard to test as
the API test harness makes this difficult at the moment.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/constellation/constellation.rs

@@ -2939,34 +2939,8 @@ where
             }
         }
 
-        let pipeline_id = match &hit_test_result {
-            Some(hit_test) => hit_test.pipeline_id,
-            None => {
-                // If there's no hit test, send to the focused browsing context of the given webview.
-                let Some(browsing_context_id) = self
-                    .webviews
-                    .get(webview_id)
-                    .map(|webview| webview.focused_browsing_context_id)
-                else {
-                    warn!("Handling InputEvent for an unknown webview: {webview_id}");
-                    return;
-                };
-
-                let Some(pipeline_id) = self
-                    .browsing_contexts
-                    .get(&browsing_context_id)
-                    .map(|context| context.pipeline_id)
-                else {
-                    warn!("{browsing_context_id}: Got InputEvent for nonexistent browsing context");
-                    return;
-                };
-
-                pipeline_id
-            },
-        };
-
-        let Some(pipeline) = self.pipelines.get(&pipeline_id) else {
-            debug!("Got event for pipeline ({pipeline_id}) after closure");
+        let Some(webview) = self.webviews.get_mut(webview_id) else {
+            warn!("Got input event for unknown WebViewId: {webview_id:?}");
             return;
         };
 
@@ -2976,13 +2950,7 @@ where
             active_keyboard_modifiers,
             event,
         };
-
-        if let Err(error) = pipeline
-            .event_loop
-            .send(ScriptThreadMessage::SendInputEvent(pipeline_id, event))
-        {
-            self.handle_send_error(pipeline_id, error);
-        }
+        webview.forward_input_event(event, &self.pipelines, &self.browsing_contexts);
     }
 
     #[servo_tracing::instrument(skip_all)]

components/constellation/constellation_webview.rs

@@ -2,9 +2,17 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use base::id::BrowsingContextId;
-use embedder_traits::Theme;
+use std::collections::HashMap;
 
+use base::id::{BrowsingContextId, PipelineId};
+use embedder_traits::{InputEvent, MouseLeaveEvent, Theme};
+use euclid::Point2D;
+use log::warn;
+use script_traits::{ConstellationInputEvent, ScriptThreadMessage};
+use style_traits::CSSPixel;
+
+use crate::browsingcontext::BrowsingContext;
+use crate::pipeline::Pipeline;
 use crate::session_history::JointSessionHistory;
 
 /// The `Constellation`'s view of a `WebView` in the embedding layer. This tracks all of the
@@ -15,6 +23,14 @@ pub(crate) struct ConstellationWebView {
     /// context.
     pub focused_browsing_context_id: BrowsingContextId,
 
+    /// The [`BrowsingContextId`] of the currently hovered browsing context, to use for
+    /// knowing which frame is currently receiving cursor events.
+    pub hovered_browsing_context_id: Option<BrowsingContextId>,
+
+    /// The last mouse move point in the coordinate space of the Pipeline that it
+    /// happened int.
+    pub last_mouse_move_point: Point2D<f32, CSSPixel>,
+
     /// The joint session history for this webview.
     pub session_history: JointSessionHistory,
 
@@ -27,6 +43,8 @@ impl ConstellationWebView {
     pub(crate) fn new(focused_browsing_context_id: BrowsingContextId) -> Self {
         Self {
             focused_browsing_context_id,
+            hovered_browsing_context_id: None,
+            last_mouse_move_point: Default::default(),
             session_history: JointSessionHistory::new(),
             theme: Theme::Light,
         }
@@ -42,4 +60,91 @@ impl ConstellationWebView {
     pub(crate) fn theme(&self) -> Theme {
         self.theme
     }
+
+    fn target_pipeline_id_for_input_event(
+        &self,
+        event: &ConstellationInputEvent,
+        browsing_contexts: &HashMap<BrowsingContextId, BrowsingContext>,
+    ) -> Option<PipelineId> {
+        if let Some(hit_test_result) = &event.hit_test_result {
+            return Some(hit_test_result.pipeline_id);
+        }
+
+        // If there's no hit test, send the event to either the hovered or focused browsing context,
+        // depending on the event type.
+        let browsing_context_id = if matches!(event.event, InputEvent::MouseLeave(_)) {
+            self.hovered_browsing_context_id
+                .unwrap_or(self.focused_browsing_context_id)
+        } else {
+            self.focused_browsing_context_id
+        };
+
+        Some(browsing_contexts.get(&browsing_context_id)?.pipeline_id)
+    }
+
+    pub(crate) fn forward_input_event(
+        &mut self,
+        event: ConstellationInputEvent,
+        pipelines: &HashMap<PipelineId, Pipeline>,
+        browsing_contexts: &HashMap<BrowsingContextId, BrowsingContext>,
+    ) {
+        let Some(pipeline_id) = self.target_pipeline_id_for_input_event(&event, browsing_contexts)
+        else {
+            warn!("Unknown pipeline for input event. Ignoring.");
+            return;
+        };
+        let Some(pipeline) = pipelines.get(&pipeline_id) else {
+            warn!("Unknown pipeline id {pipeline_id:?} for input event. Ignoring.");
+            return;
+        };
+
+        let mut update_hovered_browsing_context = |newly_hovered_browsing_context_id| {
+            let old_hovered_context_id = std::mem::replace(
+                &mut self.hovered_browsing_context_id,
+                newly_hovered_browsing_context_id,
+            );
+            if old_hovered_context_id == newly_hovered_browsing_context_id {
+                return;
+            }
+            let Some(old_hovered_context_id) = old_hovered_context_id else {
+                return;
+            };
+            let Some(pipeline) = browsing_contexts
+                .get(&old_hovered_context_id)
+                .and_then(|browsing_context| pipelines.get(&browsing_context.pipeline_id))
+            else {
+                return;
+            };
+
+            let mut synthetic_mouse_leave_event = event.clone();
+            synthetic_mouse_leave_event.event = InputEvent::MouseLeave(MouseLeaveEvent {
+                focus_moving_to_another_iframe: true,
+            });
+
+            let _ = pipeline
+                .event_loop
+                .send(ScriptThreadMessage::SendInputEvent(
+                    pipeline.id,
+                    synthetic_mouse_leave_event,
+                ));
+        };
+
+        if let InputEvent::MouseLeave(_) = &event.event {
+            update_hovered_browsing_context(None);
+            return;
+        }
+
+        if let InputEvent::MouseMove(_) = &event.event {
+            update_hovered_browsing_context(Some(pipeline.browsing_context_id));
+            self.last_mouse_move_point = event
+                .hit_test_result
+                .as_ref()
+                .expect("MouseMove events should always have hit tests.")
+                .point_in_viewport;
+        }
+
+        let _ = pipeline
+            .event_loop
+            .send(ScriptThreadMessage::SendInputEvent(pipeline.id, event));
+    }
 }