Support the AccessKit focus and blur actions (#596)

I believe this is necessary to activate and deactivate input focus with
TalkBack on Android. Assistive technologies on other platforms can also
request the focus action, though none of the AccessKit backends support
the blur action yet.

---------

Co-authored-by: Olivier FAURE <couteaubleu@gmail.com>

masonry/src/contexts.rs

@@ -301,6 +301,11 @@ impl_context_method!(
             self.widget_state.has_focus
         }
 
+        /// Whether this specific widget is in the focus chain.
+        pub fn is_in_focus_chain(&self) -> bool {
+            self.widget_state.in_focus_chain
+        }
+
         /// The disabled state of a widget.
         ///
         /// Returns `true` if this widget or any of its ancestors is explicitly disabled.
@@ -715,6 +720,7 @@ impl LifeCycleCtx<'_> {
     pub fn register_for_focus(&mut self) {
         trace!("register_for_focus");
         self.widget_state.focus_chain.push(self.widget_id());
+        self.widget_state.in_focus_chain = true;
     }
 
     /// Register this widget as accepting text input.

masonry/src/passes/accessibility.rs

@@ -46,6 +46,7 @@ fn build_accessibility_tree(
             rebuild_all,
             scale_factor,
         };
+        set_common_properties(&mut ctx);
         widget.item.accessibility(&mut ctx);
 
         let id: NodeId = ctx.widget_state.id.into();
@@ -96,20 +97,28 @@ fn build_access_node(widget: &dyn Widget, state: &WidgetState, scale_factor: f64
             .collect::<Vec<NodeId>>(),
     );
 
-    if state.is_hot {
-        node.set_hovered();
+    node
+}
+
+fn set_common_properties(ctx: &mut AccessCtx) {
+    if ctx.is_hot() {
+        ctx.current_node().set_hovered();
     }
-    if state.is_disabled {
-        node.set_disabled();
+    if ctx.is_disabled() {
+        ctx.current_node().set_disabled();
     }
-    if state.is_stashed {
-        node.set_hidden();
+    if ctx.is_stashed() {
+        ctx.current_node().set_hidden();
     }
-    if state.clip.is_some() {
-        node.set_clips_children();
+    if ctx.widget_state.clip.is_some() {
+        ctx.current_node().set_clips_children();
+    }
+    if ctx.is_in_focus_chain() && !ctx.is_disabled() {
+        ctx.current_node().add_action(accesskit::Action::Focus);
+    }
+    if ctx.is_focused() {
+        ctx.current_node().add_action(accesskit::Action::Blur);
     }
-
-    node
 }
 
 fn to_accesskit_rect(r: Rect, scale_factor: f64) -> accesskit::Rect {

masonry/src/passes/event.rs

@@ -195,6 +195,26 @@ pub(crate) fn root_on_access_event(
         event,
         false,
         |widget, ctx, event| {
+            // TODO - Split into "access_event_focus" pass or something similar.
+            if event.target == ctx.widget_id() {
+                match event.action {
+                    accesskit::Action::Focus => {
+                        if ctx.is_in_focus_chain() && !ctx.is_disabled() && !ctx.is_focused() {
+                            ctx.request_focus();
+                            ctx.set_handled();
+                            return;
+                        }
+                    }
+                    accesskit::Action::Blur => {
+                        if ctx.is_focused() {
+                            ctx.resign_focus();
+                            ctx.set_handled();
+                            return;
+                        }
+                    }
+                    _ => {}
+                }
+            }
             widget.on_access_event(ctx, event);
         },
     );

masonry/src/passes/update.rs

@@ -502,6 +502,7 @@ fn update_focus_chain_for_widget(
     state.item.has_focus = global_state.focused_widget == Some(id);
     let had_focus = state.item.has_focus;
 
+    state.item.in_focus_chain = false;
     state.item.focus_chain.clear();
     {
         let mut ctx = LifeCycleCtx {

masonry/src/widget/widget_state.rs

@@ -133,6 +133,9 @@ pub struct WidgetState {
     /// Descendants of the focused widget are not in the focused path.
     pub(crate) has_focus: bool,
 
+    /// Whether this specific widget is in the focus chain.
+    pub(crate) in_focus_chain: bool,
+
     // TODO - document
     pub(crate) is_stashed: bool,
 
@@ -179,6 +182,7 @@ impl WidgetState {
             request_accessibility: true,
             needs_accessibility: true,
             has_focus: false,
+            in_focus_chain: false,
             request_anim: true,
             needs_anim: true,
             needs_update_disabled: true,