script: Move keyboard scrolling to script (#39371)

Instead of having every single embedder implement keyboard scrolling,
handle it in script in the default key event handler. This allows
properly targeting the scroll events to their scroll containers as well
as appropriately sizing "page up" and "page down" scroll deltas.

This change means that when you use the keyboard to scroll, the focused
or most recently clicked `<iframe>` or overflow scroll container is
scrolled, rather than the main frame.

In addition, when a particular scroll frame is larger than its content
in the axis of the scroll, the scrolling operation is chained to
the parent (as in other browsers). One exception is for `<iframe>`s,
which will be implemented in a followup change.

Testing: automated tests runnable locally with `mach test-wpt --product
servodriver`

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

components/script/dom/document_event_handler.rs

@@ -18,17 +18,17 @@ use embedder_traits::{
     MouseLeftViewportEvent, ScrollEvent, TouchEvent as EmbedderTouchEvent, TouchEventType, TouchId,
     UntrustedNodeAddress, WheelEvent as EmbedderWheelEvent,
 };
-use euclid::Point2D;
+use euclid::{Point2D, Vector2D};
 use ipc_channel::ipc;
 use keyboard_types::{Code, Key, KeyState, Modifiers, NamedKey};
-use layout_api::node_id_from_scroll_id;
+use layout_api::{ScrollContainerQueryFlags, node_id_from_scroll_id};
 use script_bindings::codegen::GenericBindings::DocumentBinding::DocumentMethods;
 use script_bindings::codegen::GenericBindings::EventBinding::EventMethods;
 use script_bindings::codegen::GenericBindings::NavigatorBinding::NavigatorMethods;
 use script_bindings::codegen::GenericBindings::NodeBinding::NodeMethods;
 use script_bindings::codegen::GenericBindings::PerformanceBinding::PerformanceMethods;
 use script_bindings::codegen::GenericBindings::TouchBinding::TouchMethods;
-use script_bindings::codegen::GenericBindings::WindowBinding::WindowMethods;
+use script_bindings::codegen::GenericBindings::WindowBinding::{ScrollBehavior, WindowMethods};
 use script_bindings::inheritance::Castable;
 use script_bindings::num::Finite;
 use script_bindings::root::{Dom, DomRoot, DomSlice};
@@ -50,6 +50,7 @@ use crate::dom::gamepad::gamepadevent::GamepadEventType;
 use crate::dom::inputevent::HitTestResult;
 use crate::dom::node::{self, Node, ShadowIncluding};
 use crate::dom::pointerevent::PointerId;
+use crate::dom::scrolling_box::ScrollingBoxAxis;
 use crate::dom::types::{
     ClipboardEvent, CompositionEvent, DataTransfer, Element, Event, EventTarget, GlobalScope,
     HTMLAnchorElement, KeyboardEvent, MouseEvent, PointerEvent, Touch, TouchEvent, TouchList,
@@ -78,6 +79,8 @@ pub(crate) struct DocumentEventHandler {
     last_click_info: DomRefCell<Option<(Instant, Point2D<f32, CSSPixel>)>>,
     /// The element that is currently hovered by the cursor.
     current_hover_target: MutNullableDom<Element>,
+    /// The element that was most recently clicked.
+    most_recently_clicked_element: MutNullableDom<Element>,
     /// The most recent mouse movement point, used for processing `mouseleave` events.
     #[no_trace]
     most_recent_mousemove_point: Cell<Option<Point2D<f32, CSSPixel>>>,
@@ -100,6 +103,7 @@ impl DocumentEventHandler {
             mouse_move_event_index: Default::default(),
             last_click_info: Default::default(),
             current_hover_target: Default::default(),
+            most_recently_clicked_element: Default::default(),
             most_recent_mousemove_point: Default::default(),
             current_cursor: Default::default(),
             active_touch_points: Default::default(),
@@ -581,6 +585,8 @@ impl DocumentEventHandler {
         match event.action {
             // https://w3c.github.io/uievents/#handle-native-mouse-click
             MouseButtonAction::Click => {
+                self.most_recently_clicked_element.set(Some(&el));
+
                 el.set_click_in_progress(true);
                 dom_event.dispatch(node.upcast(), false, can_gc);
                 el.set_click_in_progress(false);
@@ -1472,4 +1478,70 @@ impl DocumentEventHandler {
             document.handle_element_scroll_event(&element);
         }
     }
+
+    pub(crate) fn run_default_keyboard_event_handler(&self, event: &KeyboardEvent) {
+        if event.upcast::<Event>().type_() != atom!("keydown") {
+            return;
+        }
+        if !event.modifiers().is_empty() {
+            return;
+        }
+
+        let scroll_axis = match event.key() {
+            Key::Named(
+                NamedKey::Home |
+                NamedKey::End |
+                NamedKey::PageDown |
+                NamedKey::PageUp |
+                NamedKey::ArrowUp |
+                NamedKey::ArrowDown,
+            ) => ScrollingBoxAxis::Y,
+            Key::Named(NamedKey::ArrowLeft | NamedKey::ArrowRight) => ScrollingBoxAxis::X,
+            _ => return,
+        };
+
+        let document = self.window.Document();
+        let mut scrolling_box = document
+            .get_focused_element()
+            .or(self.most_recently_clicked_element.get())
+            .and_then(|element| element.scrolling_box(ScrollContainerQueryFlags::Inclusive))
+            .unwrap_or_else(|| document.viewport_scrolling_box());
+
+        while !scrolling_box.can_keyboard_scroll_in_axis(scroll_axis) {
+            // Always fall back to trying to scroll the entire document.
+            if scrolling_box.is_viewport() {
+                break;
+            }
+            let parent = scrolling_box
+                .parent()
+                .unwrap_or_else(|| document.viewport_scrolling_box());
+            scrolling_box = parent;
+        }
+
+        const LINE_HEIGHT: f32 = 76.0;
+        const LINE_WIDTH: f32 = 76.0;
+
+        let current_scroll_offset = scrolling_box.scroll_position();
+        let delta = match event.key() {
+            Key::Named(NamedKey::Home) => Vector2D::new(0.0, -current_scroll_offset.y),
+            Key::Named(NamedKey::End) => Vector2D::new(
+                0.0,
+                -current_scroll_offset.y + scrolling_box.content_size().height -
+                    scrolling_box.size().height,
+            ),
+            Key::Named(NamedKey::PageDown) => {
+                Vector2D::new(0.0, scrolling_box.size().height - 2.0 * LINE_HEIGHT)
+            },
+            Key::Named(NamedKey::PageUp) => {
+                Vector2D::new(0.0, 2.0 * LINE_HEIGHT - scrolling_box.size().height)
+            },
+            Key::Named(NamedKey::ArrowUp) => Vector2D::new(0.0, -LINE_HEIGHT),
+            Key::Named(NamedKey::ArrowDown) => Vector2D::new(0.0, LINE_HEIGHT),
+            Key::Named(NamedKey::ArrowLeft) => Vector2D::new(-LINE_WIDTH, 0.0),
+            Key::Named(NamedKey::ArrowRight) => Vector2D::new(LINE_WIDTH, 0.0),
+            _ => return,
+        };
+
+        scrolling_box.scroll_to(delta + current_scroll_offset, ScrollBehavior::Auto);
+    }
 }