Add a special aria-label for 'copy to marked spot' button to indicate the cause of its being disabled.

accessible/clipboard.service.js

@@ -61,6 +61,9 @@ blocklyApp.ClipboardService = ng.core
         return this.markedConnection_.getSourceBlock();
       }
     },
+    isAnyConnectionMarked: function() {
+      return Boolean(this.markedConnection_);
+    },
     isMovableToMarkedConnection: function(block) {
       // It should not be possible to move any ancestor of the block containing
       // the marked spot to the marked spot.

accessible/messages.js

@@ -32,7 +32,7 @@ Blockly.Msg.WORKSPACE_BLOCK = 'workspace block. Move right to view submenu.';
 Blockly.Msg.CLEAR_WORKSPACE = 'Erase Workspace';
 
 Blockly.Msg.COPY_TO_CLIPBOARD = 'Copy to clipboard.';
-Blockly.Msg.COPY_TO_MARKED_SPOT = 'Copy to link.';
+Blockly.Msg.COPY_TO_MARKED_SPOT = 'Attach to link.';
 Blockly.Msg.COPY_TO_WORKSPACE = 'Add to workspace.';
 
 Blockly.Msg.COPY_BLOCK = 'Copy block.';

accessible/toolbox-tree.component.js

@@ -42,7 +42,7 @@ blocklyApp.ToolboxTreeComponent = ng.core
           </button>
         </li>
         <li [id]="idMap['sendToSelected']" role="treeitem" *ngIf="!isWorkspaceEmpty()"
-            [attr.aria-labelledBy]="generateAriaLabelledByAttr(idMap['sendToSelectedButton'], 'blockly-button')"
+            [attr.aria-label]="getAriaLabelForCopyToMarkedSpotButton()"
             [attr.aria-level]="level + 1"
             [attr.aria-disabled]="!canBeCopiedToMarkedConnection()">
           <button [id]="idMap['sendToSelectedButton']" (click)="copyToMarkedSpot()"
@@ -105,6 +105,14 @@ blocklyApp.ToolboxTreeComponent = ng.core
         });
       }
     },
+    getAriaLabelForCopyToMarkedSpotButton: function() {
+      // TODO(sll): Find a way to make this more like the other buttons.
+      var ariaLabel = 'Attach to link button';
+      if (!this.clipboardService.isAnyConnectionMarked()) {
+        ariaLabel += ', unavailable. Add a link in the workspace first.';
+      }
+      return ariaLabel;
+    },
     isWorkspaceEmpty: function() {
       return this.utilsService.isWorkspaceEmpty();
     },