fix: dragging shadow blocks

core/block_svg.ts

@@ -243,16 +243,19 @@ export class BlockSvg
 
   /** Selects this block. Highlights the block visually. */
   select() {
-    if (this.isShadow() && this.getParent()) {
-      // Shadow blocks should not be selected.
-      this.getParent()!.select();
+    if (this.isShadow()) {
+      this.getParent()?.select();
       return;
     }
     this.addSelect();
   }
 
   /** Unselects this block. Unhighlights the blockv visually.   */
   unselect() {
+    if (this.isShadow()) {
+      this.getParent()?.unselect();
+      return;
+    }
     this.removeSelect();
   }
 

core/dragging/block_drag_strategy.ts

@@ -55,15 +55,24 @@ export class BlockDragStrategy implements IDragStrategy {
 
   private dragging = false;
 
+  /**
+   * If this is a shadow block, the offset between this block and the parent
+   * block, to add to the drag location. In workspace units.
+   */
+  private dragOffset = new Coordinate(0, 0);
+
   constructor(private block: BlockSvg) {
     this.workspace = block.workspace;
   }
 
   /** Returns true if the block is currently movable. False otherwise. */
   isMovable(): boolean {
+    if (this.block.isShadow()) {
+      return this.block.getParent()?.isMovable() ?? false;
+    }
+
     return (
       this.block.isOwnMovable() &&
-      !this.block.isShadow() &&
       !this.block.isDeadOrDying() &&
       !this.workspace.options.readOnly &&
       // We never drag blocks in the flyout, only create new blocks that are
@@ -77,6 +86,11 @@ export class BlockDragStrategy implements IDragStrategy {
    * from any parent blocks.
    */
   startDrag(e?: PointerEvent): void {
+    if (this.block.isShadow()) {
+      this.startDraggingShadow(e);
+      return;
+    }
+
     this.dragging = true;
     if (!eventUtils.getGroup()) {
       eventUtils.setGroup(true);
@@ -106,6 +120,22 @@ export class BlockDragStrategy implements IDragStrategy {
     this.workspace.getLayerManager()?.moveToDragLayer(this.block);
   }
 
+  /** Starts a drag on a shadow, recording the drag offset. */
+  private startDraggingShadow(e?: PointerEvent) {
+    const parent = this.block.getParent();
+    if (!parent) {
+      throw new Error(
+        'Tried to drag a shadow block with no parent. ' +
+          'Shadow blocks should always have parents.',
+      );
+    }
+    this.dragOffset = Coordinate.difference(
+      parent.getRelativeToSurfaceXY(),
+      this.block.getRelativeToSurfaceXY(),
+    );
+    parent.startDrag(e);
+  }
+
   /**
    * Whether or not we should disconnect the block when a drag is started.
    *
@@ -174,6 +204,11 @@ export class BlockDragStrategy implements IDragStrategy {
 
   /** Moves the block and updates any connection previews. */
   drag(newLoc: Coordinate): void {
+    if (this.block.isShadow()) {
+      this.block.getParent()?.drag(Coordinate.sum(newLoc, this.dragOffset));
+      return;
+    }
+
     this.block.moveDuringDrag(newLoc);
     this.updateConnectionPreview(
       this.block,
@@ -317,7 +352,12 @@ export class BlockDragStrategy implements IDragStrategy {
    * Cleans up any state at the end of the drag. Applies any pending
    * connections.
    */
-  endDrag(): void {
+  endDrag(e?: PointerEvent): void {
+    if (this.block.isShadow()) {
+      this.block.getParent()?.endDrag(e);
+      return;
+    }
+
     this.fireDragEndEvent();
     this.fireMoveEvent();
 
@@ -373,6 +413,11 @@ export class BlockDragStrategy implements IDragStrategy {
    * including reconnecting connections.
    */
   revertDrag(): void {
+    if (this.block.isShadow()) {
+      this.block.getParent()?.revertDrag();
+      return;
+    }
+
     this.startChildConn?.connect(this.block.nextConnection);
     if (this.startParentConn) {
       switch (this.startParentConn.type) {