feat: Make Flyout an ARIA list (experimental) (#9528)

## The basics

- [x] I [validated my changes](https://developers.google.com/blockly/guides/contribute/core#making_and_verifying_a_change)

## The details
### Resolves

Fixes #9495

### Proposed Changes

Changes a bunch of ARIA role & label management to ensure that `Flyout` acts like a list rather than a tree.

### Reason for Changes

`Flyout`s are always hierarchically flat so it doesn't make sense to model them as a tree. Instead, a menu is likely a better fit per https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Reference/Roles/menu_role:

> A `menu` generally represents a grouping of common actions or functions that the user can invoke. The `menu` role is appropriate when a list of menu items is presented in a manner similar to a menu on a desktop application. Submenus, also known as pop-up menus, also have the role `menu`.

However, there are important caveats that need to be considered and addressed:
- As discussed below, menus introduce some unexpected compatibility issues with VoiceOver so this PR presently uses `list` and `listitem`s as a slightly more generic enumerating alternative for menus.
- Menus (and to some extent lists) are stricter\* than trees in that they seem to impose a requirement that `menuitem`s cannot contain interactive elements (they are expected to be interactive themselves). This has led to a few specific changes:
  - Block children are now hidden when in the flyout (since they aren't navigable anyway).
  - Flyout buttons are themselves now the `menuitem` rather than their container parent, and they no longer use the role button.
- Menus aren't really expected to contain labels but it isn't inherently disallowed. This is less of an issue with lists.
- Because everything must be a `listitem` (or a few more specific alternatives) both blocks and buttons lack some context. Since not all `Flyout` items can be expected to be interactive, buttons and blocks have both had their labels updated to include an explicit indicator that they are buttons and blocks, respectively. Note that this does possibly go against convention for buttons in particular but it seems fine since this is an unusual (but seemingly correct) utilization of a `list` element.
- To further provide context on blocks, the generated label for blocks in the `Flyout` is now its verbose label rather than the more compact form.

\* This is largely a consequence of a few specific attributes of `menuitem` and `menu`s as a whole and very likely also applies to `tree`s and `treeitem`s (and `list`s and `listitems`s). However, now seemed like a good time to fix this especially in case some screen readers get confused rather than ignore nested interactive controls/follow semantic cloaking per the spec.

Demo of it working on VoiceOver (per @gonfunko -- note this was the `menu` variant rather than the `list` variant of the PR):

![Screen Recording 2025-12-11 at 2 50 30 PM](https://github.com/user-attachments/assets/24c4389f-73c7-4cb5-96ce-d9666841cdd8)

### Test Coverage

This has been manually tested with ChromeVox. No automated tests are needed as part of this experimental change.

### Documentation

No new documentation changes are needed for this experimental change.

### Additional Information

None.

core/block_svg.ts

@@ -239,10 +239,16 @@ export class BlockSvg
     aria.setState(
       this.getFocusableElement(),
       aria.State.LABEL,
-      this.computeAriaLabel(),
+      !this.isInFlyout
+        ? this.computeAriaLabel()
+        : this.computeAriaLabelForFlyoutBlock(),
     );
   }
 
+  private computeAriaLabelForFlyoutBlock(): string {
+    return `${this.computeAriaLabel(true)}, block`;
+  }
+
   computeAriaLabel(
     verbose: boolean = false,
     minimal: boolean = false,
@@ -305,7 +311,7 @@ export class BlockSvg
 
   private computeAriaRole() {
     if (this.workspace.isFlyout) {
-      aria.setRole(this.pathObject.svgPath, aria.Role.TREEITEM);
+      aria.setRole(this.pathObject.svgPath, aria.Role.LISTITEM);
     } else {
       const roleDescription = this.getAriaRoleDescription();
       aria.setState(

core/field_checkbox.ts

@@ -122,13 +122,18 @@ export class FieldCheckbox extends Field<CheckboxBool> {
 
   private recomputeAria() {
     const element = this.getFocusableElement();
-    aria.setRole(element, aria.Role.CHECKBOX);
-    aria.setState(
-      element,
-      aria.State.LABEL,
-      this.getAriaTypeName() ?? 'Checkbox',
-    );
-    aria.setState(element, aria.State.CHECKED, !!this.value_);
+    const isInFlyout = this.getSourceBlock()?.workspace?.isFlyout || false;
+    if (!isInFlyout) {
+      aria.setRole(element, aria.Role.CHECKBOX);
+      aria.setState(
+        element,
+        aria.State.LABEL,
+        this.getAriaTypeName() ?? 'Checkbox',
+      );
+      aria.setState(element, aria.State.CHECKED, !!this.value_);
+    } else {
+      aria.setState(element, aria.State.HIDDEN, true);
+    }
   }
 
   override render_() {

core/field_dropdown.ts

@@ -208,17 +208,21 @@ export class FieldDropdown extends Field<string> {
 
   protected recomputeAria() {
     if (!this.fieldGroup_) return; // There's no element to set currently.
+    const isInFlyout = this.getSourceBlock()?.workspace?.isFlyout || false;
     const element = this.getFocusableElement();
-    aria.setRole(element, aria.Role.COMBOBOX);
-    aria.setState(element, aria.State.HASPOPUP, aria.Role.LISTBOX);
-    aria.setState(element, aria.State.EXPANDED, !!this.menu_);
-    if (this.menu_) {
-      aria.setState(element, aria.State.CONTROLS, this.menu_.id);
+    if (!isInFlyout) {
+      aria.setRole(element, aria.Role.COMBOBOX);
+      aria.setState(element, aria.State.HASPOPUP, aria.Role.LISTBOX);
+      aria.setState(element, aria.State.EXPANDED, !!this.menu_);
+      if (this.menu_) {
+        aria.setState(element, aria.State.CONTROLS, this.menu_.id);
+      } else {
+        aria.clearState(element, aria.State.CONTROLS);
+      }
+      aria.setState(element, aria.State.LABEL, super.computeAriaLabel(true));
     } else {
-      aria.clearState(element, aria.State.CONTROLS);
+      aria.setState(element, aria.State.HIDDEN, true);
     }
-
-    aria.setState(element, aria.State.LABEL, super.computeAriaLabel(true));
   }
 
   /**

core/field_image.ts

@@ -159,13 +159,14 @@ export class FieldImage extends Field<string> {
       dom.addClass(this.fieldGroup_, 'blocklyImageField');
     }
 
+    const isInFlyout = this.getSourceBlock()?.workspace?.isFlyout || false;
     const element = this.getFocusableElement();
-    if (this.isClickable()) {
+    if (!isInFlyout && this.isClickable()) {
       this.imageElement.style.cursor = 'pointer';
       aria.setRole(element, aria.Role.BUTTON);
       aria.setState(element, aria.State.LABEL, super.computeAriaLabel(true));
     } else {
-      // The field isn't navigable unless it's clickable.
+      // The field isn't navigable unless it's clickable and outside the flyout.
       aria.setRole(element, aria.Role.PRESENTATION);
     }
   }

core/field_input.ts

@@ -178,8 +178,6 @@ export abstract class FieldInput<T extends InputTypes> extends Field<
       dom.addClass(this.fieldGroup_, 'blocklyInputField');
     }
 
-    const element = this.getFocusableElement();
-    aria.setRole(element, aria.Role.BUTTON);
     this.recomputeAriaLabel();
   }
 
@@ -189,7 +187,13 @@ export abstract class FieldInput<T extends InputTypes> extends Field<
   protected recomputeAriaLabel() {
     if (!this.fieldGroup_) return;
     const element = this.getFocusableElement();
-    aria.setState(element, aria.State.LABEL, super.computeAriaLabel());
+    const isInFlyout = this.getSourceBlock()?.workspace?.isFlyout || false;
+    if (!isInFlyout) {
+      aria.setRole(element, aria.Role.BUTTON);
+      aria.setState(element, aria.State.LABEL, super.computeAriaLabel());
+    } else {
+      aria.setState(element, aria.State.HIDDEN, true);
+    }
   }
 
   override isFullBlockField(): boolean {

core/flyout_button.ts

@@ -132,12 +132,13 @@ export class FlyoutButton
       this.svgContainerGroup,
     );
 
-    aria.setRole(this.svgContainerGroup, aria.Role.TREEITEM);
     if (this.isFlyoutLabel) {
+      aria.setRole(this.svgContainerGroup, aria.Role.LISTITEM);
       aria.setRole(this.svgContentGroup, aria.Role.PRESENTATION);
       this.svgFocusableGroup = this.svgContainerGroup;
     } else {
-      aria.setRole(this.svgContentGroup, aria.Role.BUTTON);
+      aria.setRole(this.svgContainerGroup, aria.Role.PRESENTATION);
+      aria.setRole(this.svgContentGroup, aria.Role.LISTITEM);
       this.svgFocusableGroup = this.svgContentGroup;
     }
     this.svgFocusableGroup.id = this.id;
@@ -183,9 +184,7 @@ export class FlyoutButton
       },
       this.svgContentGroup,
     );
-    if (!this.isFlyoutLabel) {
-      aria.setRole(svgText, aria.Role.PRESENTATION);
-    }
+    aria.setRole(svgText, aria.Role.PRESENTATION);
     let text = parsing.replaceMessageReferences(this.text);
     if (this.workspace.RTL) {
       // Force text to be RTL by adding an RLM.
@@ -198,7 +197,15 @@ export class FlyoutButton
         .getThemeManager()
         .subscribe(this.svgText, 'flyoutForegroundColour', 'fill');
     }
-    aria.setState(this.svgFocusableGroup, aria.State.LABEL, text);
+    if (this.isFlyoutLabel) {
+      aria.setState(this.svgFocusableGroup, aria.State.LABEL, text);
+    } else {
+      aria.setState(
+        this.svgFocusableGroup,
+        aria.State.LABEL,
+        `${text}, button`,
+      );
+    }
 
     const fontSize = style.getComputedStyle(svgText, 'fontSize');
     const fontWeight = style.getComputedStyle(svgText, 'fontWeight');

core/flyout_item.ts

@@ -8,6 +8,11 @@ export class FlyoutItem {
   /**
    * Creates a new FlyoutItem.
    *
+   * Note that it's the responsibility of implementations to ensure that element
+   * is given the ARIA role LISTITEM and respects its expected constraints
+   * (which includes ensuring that no interactive elements are children of the
+   * item element--interactive elements themselves should be the LISTITEM).
+   *
    * @param element The element that will be displayed in the flyout.
    * @param type The type of element. Should correspond to the type of the
    *     flyout inflater that created this object.

core/utils/aria.ts

@@ -28,6 +28,7 @@ export enum Role {
 
   // ARIA role for menu item elements.
   MENUITEM = 'menuitem',
+
   // ARIA role for option items that are  children of combobox, listbox, menu,
   // radiogroup, or tree elements.
   OPTION = 'option',
@@ -55,6 +56,8 @@ export enum Role {
   SPINBUTTON = 'spinbutton',
   REGION = 'region',
   GENERIC = 'generic',
+  LIST = 'list',
+  LISTITEM = 'listitem',
 }
 
 /**

core/workspace_svg.ts

@@ -804,8 +804,8 @@ export class WorkspaceSvg
     this.svgBubbleCanvas_ = this.layerManager.getBubbleLayer();
 
     if (this.isFlyout) {
-      // Use the block canvas as the primary tree parent for flyout blocks.
-      aria.setRole(this.svgBlockCanvas_, aria.Role.TREE);
+      // Use the block canvas as the primary list for nesting.
+      aria.setRole(this.svgBlockCanvas_, aria.Role.LIST);
       aria.setState(this.svgBlockCanvas_, aria.State.LABEL, ariaLabel);
     } else {
       browserEvents.conditionalBind(