feat: Add initial support for screen readers (experimental) (#9280)

## The basics

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

## The details
### Resolves

Fixes part of #8207
Fixes part of #3370

### Proposed Changes

This introduces initial broad ARIA integration in order to enable at least basic screen reader support when using keyboard navigation.

Largely this involves introducing ARIA roles and labels in a bunch of places, sometimes done in a way to override normal built-in behaviors of the accessibility node tree in order to get a richer first-class output for Blockly (such as for blocks and workspaces).

### Reason for Changes

ARIA is the fundamental basis for configuring how focusable nodes in Blockly are represented to the user when using a screen reader. As such, all focusable nodes requires labels and roles in order to correctly communicate their contexts.

The specific approach taken in this PR is to simply add labels and roles to all nodes where obvious with some extra work done for `WorkspaceSvg` and `BlockSvg` in order to represent blocks as a tree (since that seems to be the best fitting ARIA role per those available: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Reference/Roles). The custom work specifically for blocks includes:
- Overriding the role description to be 'block' rather than 'tree item' (which is the default).
- Overriding the position, level, and number of sibling counts since those are normally determined based on the DOM tree and blocks are not laid out in the tree the same way they are visually or logically (so these computations were incorrect). This is also the reason for a bunch of extra computation logic being introduced.

One note on some of the labels being nonsensical (e.g. 'DoNotOverride?'): this was done intentionally to try and ensure _all_ focusable nodes (that can be focused) have labels, even when the specifics of what that label should be aren't yet clear. More components had these temporary labels until testing revealed how exactly they would behave from a screen reader perspective (at which point their roles and labels were updated as needed). The temporary labels act as an indicator when navigating through the UI, and some of the nodes can't easily be reached (for reasons) and thus may never actually need a label. More work is needed in understanding both what components need labels and what those labels should be, but that will be done beyond this PR.

### Test Coverage

No tests are added to this as it's experimental and not a final implementation.

The keyboard navigation tests are failing due to a visibility expansion of `connectionCandidate` in `BlockDragStrategy`. There's no way to avoid this breakage, unfortunately. Instead, this PR will be merged and then RaspberryPiFoundation/blockly-keyboard-experimentation#684 will be finalized and merged to fix it. There's some additional work that will happen both in that branch and in a later PR in core Blockly to integrate the two experimentation branches as part of #9283 so that CI passes correctly for both branches.

### Documentation

No documentation is needed at this time.

### Additional Information

This work is experimental and is meant to serve two purposes:
- Provide a foundation for testing and iterating the core screen reader experience in Blockly.
- Provide a reference point for designing a long-term solution that accounts for all requirements collected during user testing.

This code should never be merged into `develop` as it stands. Instead, it will be redesigned with maintainability, testing, and correctness in mind at a future date (see RaspberryPiFoundation/blockly-keyboard-experimentation#673).

Author: BenHenning

core/block_svg.ts

@@ -56,6 +56,7 @@ import * as blocks from './serialization/blocks.js';
 import type {BlockStyle} from './theme.js';
 import * as Tooltip from './tooltip.js';
 import {idGenerator} from './utils.js';
+import * as aria from './utils/aria.js';
 import {Coordinate} from './utils/coordinate.js';
 import * as dom from './utils/dom.js';
 import {Rect} from './utils/rect.js';
@@ -168,6 +169,8 @@ export class BlockSvg
   /** Whether this block is currently being dragged. */
   private dragging = false;
 
+  public currentConnectionCandidate: RenderedConnection | null = null;
+
   /**
    * The location of the top left of this block (in workspace coordinates)
    * relative to either its parent block, or the workspace origin if it has no
@@ -215,7 +218,69 @@ export class BlockSvg
     // The page-wide unique ID of this Block used for focusing.
     svgPath.id = idGenerator.getNextUniqueId();
 
+    aria.setState(svgPath, aria.State.ROLEDESCRIPTION, 'block');
+    aria.setRole(svgPath, aria.Role.TREEITEM);
+    svgPath.tabIndex = -1;
+    this.currentConnectionCandidate = null;
+
     this.doInit_();
+
+    // Note: This must be done after initialization of the block's fields.
+    this.recomputeAriaLabel();
+  }
+
+  private recomputeAriaLabel() {
+    aria.setState(
+      this.getFocusableElement(),
+      aria.State.LABEL,
+      this.computeAriaLabel(),
+    );
+  }
+
+  private computeAriaLabel(): string {
+    // Guess the block's aria label based on its field labels.
+    if (this.isShadow()) {
+      // TODO: Shadows may have more than one field.
+      // Shadow blocks are best represented directly by their field since they
+      // effectively operate like a field does for keyboard navigation purposes.
+      const field = Array.from(this.getFields())[0];
+      return (
+        aria.getState(field.getFocusableElement(), aria.State.LABEL) ??
+        'Unknown?'
+      );
+    }
+
+    const fieldLabels = [];
+    for (const field of this.getFields()) {
+      if (field instanceof FieldLabel) {
+        fieldLabels.push(field.getText());
+      }
+    }
+    return fieldLabels.join(' ');
+  }
+
+  collectSiblingBlocks(surroundParent: BlockSvg | null): BlockSvg[] {
+    // NOTE TO DEVELOPERS: it's very important that these are NOT sorted. The
+    // returned list needs to be relatively stable for consistency block indexes
+    // read out to users via screen readers.
+    if (surroundParent) {
+      // Start from the first sibling and iterate in navigation order.
+      const firstSibling: BlockSvg = surroundParent.getChildren(false)[0];
+      const siblings: BlockSvg[] = [firstSibling];
+      let nextSibling: BlockSvg | null = firstSibling;
+      while ((nextSibling = nextSibling.getNextBlock())) {
+        siblings.push(nextSibling);
+      }
+      return siblings;
+    } else {
+      // For top-level blocks, simply return those from the workspace.
+      return this.workspace.getTopBlocks(false);
+    }
+  }
+
+  computeLevelInWorkspace(): number {
+    const surroundParent = this.getSurroundParent();
+    return surroundParent ? surroundParent.computeLevelInWorkspace() + 1 : 0;
   }
 
   /**
@@ -266,12 +331,14 @@ export class BlockSvg
   select() {
     this.addSelect();
     common.fireSelectedEvent(this);
+    aria.setState(this.getFocusableElement(), aria.State.SELECTED, true);
   }
 
   /** Unselects this block. Unhighlights the block visually. */
   unselect() {
     this.removeSelect();
     common.fireSelectedEvent(null);
+    aria.setState(this.getFocusableElement(), aria.State.SELECTED, false);
   }
 
   /**
@@ -342,6 +409,8 @@ export class BlockSvg
     }
 
     this.applyColour();
+
+    this.workspace.recomputeAriaTree();
   }
 
   /**
@@ -1776,21 +1845,32 @@ export class BlockSvg
   /** Starts a drag on the block. */
   startDrag(e?: PointerEvent): void {
     this.dragStrategy.startDrag(e);
+    const dragStrategy = this.dragStrategy as BlockDragStrategy;
+    const candidate = dragStrategy.connectionCandidate?.neighbour ?? null;
+    this.currentConnectionCandidate = candidate;
+    this.announceDynamicAriaState(true, false);
   }
 
   /** Drags the block to the given location. */
   drag(newLoc: Coordinate, e?: PointerEvent): void {
     this.dragStrategy.drag(newLoc, e);
+    const dragStrategy = this.dragStrategy as BlockDragStrategy;
+    const candidate = dragStrategy.connectionCandidate?.neighbour ?? null;
+    this.currentConnectionCandidate = candidate;
+    this.announceDynamicAriaState(true, false, newLoc);
   }
 
   /** Ends the drag on the block. */
   endDrag(e?: PointerEvent): void {
     this.dragStrategy.endDrag(e);
+    this.currentConnectionCandidate = null;
+    this.announceDynamicAriaState(false, false);
   }
 
   /** Moves the block back to where it was at the start of a drag. */
   revertDrag(): void {
     this.dragStrategy.revertDrag();
+    this.announceDynamicAriaState(false, true);
   }
 
   /**
@@ -1855,4 +1935,53 @@ export class BlockSvg
   canBeFocused(): boolean {
     return true;
   }
+
+  /**
+   * Announces the current dynamic state of the specified block, if any.
+   *
+   * An example of dynamic state is whether the block is currently being moved,
+   * and in what way. These states aren't represented through ARIA directly, so
+   * they need to be determined and announced using an ARIA live region
+   * (see aria.announceDynamicAriaState).
+   *
+   * @param isMoving Whether the specified block is currently being moved.
+   * @param isCanceled Whether the previous movement operation has been canceled.
+   * @param newLoc The new location the block is moving to (if unconstrained).
+   */
+  private announceDynamicAriaState(
+    isMoving: boolean,
+    isCanceled: boolean,
+    newLoc?: Coordinate,
+  ) {
+    if (isCanceled) {
+      aria.announceDynamicAriaState('Canceled movement');
+      return;
+    }
+    if (!isMoving) return;
+    if (this.currentConnectionCandidate) {
+      // TODO: Figure out general detachment.
+      // TODO: Figure out how to deal with output connections.
+      const surroundParent = this.currentConnectionCandidate.sourceBlock_;
+      const announcementContext = [];
+      announcementContext.push('Moving'); // TODO: Specialize for inserting?
+      // NB: Old code here doesn't seem to handle parents correctly.
+      if (this.currentConnectionCandidate.type === ConnectionType.INPUT_VALUE) {
+        announcementContext.push('to', 'input');
+      } else {
+        announcementContext.push('to', 'child');
+      }
+      if (surroundParent) {
+        announcementContext.push('of', surroundParent.computeAriaLabel());
+      }
+
+      // If the block is currently being moved, announce the new block label so that the user understands where it is now.
+      // TODO: Figure out how much recomputeAriaTreeItemDetailsRecursively needs to anticipate position if it won't be reannounced, and how much of that context should be included in the liveannouncement.
+      aria.announceDynamicAriaState(announcementContext.join(' '));
+    } else if (newLoc) {
+      // The block is being freely dragged.
+      aria.announceDynamicAriaState(
+        `Moving unconstrained to coordinate x ${Math.round(newLoc.x)} and y ${Math.round(newLoc.y)}.`,
+      );
+    }
+  }
 }

core/bubbles/bubble.ts

@@ -15,6 +15,7 @@ import type {IHasBubble} from '../interfaces/i_has_bubble.js';
 import {ISelectable} from '../interfaces/i_selectable.js';
 import {ContainerRegion} from '../metrics_manager.js';
 import {Scrollbar} from '../scrollbar.js';
+import * as aria from '../utils/aria.js';
 import {Coordinate} from '../utils/coordinate.js';
 import * as dom from '../utils/dom.js';
 import * as idGenerator from '../utils/idgenerator.js';
@@ -142,6 +143,8 @@ export abstract class Bubble implements IBubble, ISelectable, IFocusableNode {
 
     this.focusableElement = overriddenFocusableElement ?? this.svgRoot;
     this.focusableElement.setAttribute('id', this.id);
+    aria.setRole(this.focusableElement, aria.Role.GROUP);
+    aria.setState(this.focusableElement, aria.State.LABEL, 'Bubble');
 
     browserEvents.conditionalBind(
       this.background,

core/comments/collapse_comment_bar_button.ts

@@ -6,6 +6,7 @@
 
 import * as browserEvents from '../browser_events.js';
 import * as touch from '../touch.js';
+import * as aria from '../utils/aria.js';
 import * as dom from '../utils/dom.js';
 import {Svg} from '../utils/svg.js';
 import type {WorkspaceSvg} from '../workspace_svg.js';
@@ -69,6 +70,11 @@ export class CollapseCommentBarButton extends CommentBarButton {
     browserEvents.unbind(this.bindId);
   }
 
+  override initAria(): void {
+    aria.setRole(this.icon, aria.Role.BUTTON);
+    aria.setState(this.icon, aria.State.LABEL, 'DoNotDefine?');
+  }
+
   /**
    * Adjusts the positioning of this button within its container.
    */

core/comments/comment_bar_button.ts

@@ -52,6 +52,8 @@ export abstract class CommentBarButton implements IFocusableNode {
     return comment;
   }
 
+  abstract initAria(): void;
+
   /** Adjusts the position of this button within its parent container. */
   abstract reposition(): void;
 

core/comments/comment_editor.ts

@@ -9,6 +9,7 @@ import {getFocusManager} from '../focus_manager.js';
 import {IFocusableNode} from '../interfaces/i_focusable_node.js';
 import {IFocusableTree} from '../interfaces/i_focusable_tree.js';
 import * as touch from '../touch.js';
+import * as aria from '../utils/aria.js';
 import * as dom from '../utils/dom.js';
 import {Size} from '../utils/size.js';
 import {Svg} from '../utils/svg.js';
@@ -54,6 +55,8 @@ export class CommentEditor implements IFocusableNode {
     ) as HTMLTextAreaElement;
     this.textArea.setAttribute('tabindex', '-1');
     this.textArea.setAttribute('dir', this.workspace.RTL ? 'RTL' : 'LTR');
+    aria.setRole(this.textArea, aria.Role.TEXTBOX);
+    aria.setState(this.textArea, aria.State.LABEL, 'DoNotDefine?');
     dom.addClass(this.textArea, 'blocklyCommentText');
     dom.addClass(this.textArea, 'blocklyTextarea');
     dom.addClass(this.textArea, 'blocklyText');

core/comments/comment_view.ts

@@ -10,6 +10,7 @@ import type {IFocusableNode} from '../interfaces/i_focusable_node';
 import {IRenderedElement} from '../interfaces/i_rendered_element.js';
 import * as layers from '../layers.js';
 import * as touch from '../touch.js';
+import * as aria from '../utils/aria.js';
 import {Coordinate} from '../utils/coordinate.js';
 import * as dom from '../utils/dom.js';
 import * as drag from '../utils/drag.js';
@@ -108,6 +109,9 @@ export class CommentView implements IRenderedElement {
       'class': 'blocklyComment blocklyEditable blocklyDraggable',
     });
 
+    aria.setRole(this.svgRoot, aria.Role.TEXTBOX);
+    aria.setState(this.svgRoot, aria.State.LABEL, 'DoNotOverride?');
+
     this.highlightRect = this.createHighlightRect(this.svgRoot);
 
     ({

core/comments/delete_comment_bar_button.ts

@@ -7,6 +7,7 @@
 import * as browserEvents from '../browser_events.js';
 import {getFocusManager} from '../focus_manager.js';
 import * as touch from '../touch.js';
+import * as aria from '../utils/aria.js';
 import * as dom from '../utils/dom.js';
 import {Svg} from '../utils/svg.js';
 import type {WorkspaceSvg} from '../workspace_svg.js';
@@ -69,6 +70,11 @@ export class DeleteCommentBarButton extends CommentBarButton {
     browserEvents.unbind(this.bindId);
   }
 
+  override initAria(): void {
+    aria.setRole(this.icon, aria.Role.BUTTON);
+    aria.setState(this.icon, aria.State.LABEL, 'DoNotDefine?');
+  }
+
   /**
    * Adjusts the positioning of this button within its container.
    */

core/css.ts

@@ -507,4 +507,12 @@ input[type=number] {
 ) {
   outline: none;
 }
+
+#blocklyAriaAnnounce {
+  position: absolute;
+  left: -9999px;
+  width: 1px;
+  height: px;
+  overflow: hidden;
+}
 `;

core/dragging/block_drag_strategy.ts

@@ -50,7 +50,7 @@ export class BlockDragStrategy implements IDragStrategy {
 
   private startLoc: Coordinate | null = null;
 
-  private connectionCandidate: ConnectionCandidate | null = null;
+  public connectionCandidate: ConnectionCandidate | null = null;
 
   private connectionPreviewer: IConnectionPreviewer | null = null;
 

core/field.ts

@@ -31,6 +31,7 @@ import {ISerializable} from './interfaces/i_serializable.js';
 import type {ConstantProvider} from './renderers/common/constants.js';
 import type {KeyboardShortcut} from './shortcut_registry.js';
 import * as Tooltip from './tooltip.js';
+import * as aria from './utils/aria.js';
 import type {Coordinate} from './utils/coordinate.js';
 import * as dom from './utils/dom.js';
 import * as idGenerator from './utils/idgenerator.js';
@@ -403,6 +404,7 @@ export abstract class Field<T = any>
     }
     this.textContent_ = document.createTextNode('');
     this.textElement_.appendChild(this.textContent_);
+    aria.setState(this.textElement_, aria.State.HIDDEN, true);
   }
 
   /**