Add API to IDragTarget to prevent block move (#4886)

core/block_dragger.js

@@ -265,8 +265,14 @@ Blockly.BlockDragger.prototype.endDrag = function(e, currentDragDeltaXY) {
 
   Blockly.blockAnimations.disconnectUiStop();
 
-  var delta = this.pixelsToWorkspaceUnits_(currentDragDeltaXY);
-  var newLoc = Blockly.utils.Coordinate.sum(this.startXY_, delta);
+  var preventMove = !!this.dragTarget_ &&
+      this.dragTarget_.shouldPreventBlockMove(this.draggingBlock_);
+  if (preventMove) {
+    var newLoc = this.startXY_;
+  } else {
+    var delta = this.pixelsToWorkspaceUnits_(currentDragDeltaXY);
+    var newLoc = Blockly.utils.Coordinate.sum(this.startXY_, delta);
+  }
   this.draggingBlock_.moveOffDragSurface(newLoc);
 
   if (this.dragTarget_) {
@@ -279,8 +285,17 @@ Blockly.BlockDragger.prototype.endDrag = function(e, currentDragDeltaXY) {
     this.draggingBlock_.dispose(false, true);
     Blockly.draggingConnections = [];
   } else {
-    // Moving the block is expensive, so only do it if the block is not deleted.
-    this.updateBlockAfterMove_(delta);
+    this.draggingBlock_.setDragging(false);
+    if (delta) { // !preventMove
+      this.updateBlockLocationAfterMove_(delta);
+    } else {
+      // Blocks dragged directly from a flyout may need to be bumped into
+      // bounds.
+      Blockly.bumpObjectIntoBounds_(
+          this.draggingBlock_.workspace,
+          this.workspace_.getMetricsManager()
+              .getScrollMetrics(true), this.draggingBlock_);
+    }
   }
   this.workspace_.setResizesEnabled(true);
 
@@ -293,9 +308,8 @@ Blockly.BlockDragger.prototype.endDrag = function(e, currentDragDeltaXY) {
  *     the block started the drag to where it ended the drag.
  * @protected
  */
-Blockly.BlockDragger.prototype.updateBlockAfterMove_ = function(delta) {
+Blockly.BlockDragger.prototype.updateBlockLocationAfterMove_ = function(delta) {
   this.draggingBlock_.moveConnections(delta.x, delta.y);
-  this.draggingBlock_.setDragging(false);
   this.fireMoveEvent_();
   if (this.draggedConnectionManager_.wouldConnectBlock()) {
     // Applying connections also rerenders the relevant blocks.

core/bubble_dragger.js

@@ -194,8 +194,14 @@ Blockly.BubbleDragger.prototype.endBubbleDrag = function(
   // Make sure internal state is fresh.
   this.dragBubble(e, currentDragDeltaXY);
 
-  var delta = this.pixelsToWorkspaceUnits_(currentDragDeltaXY);
-  var newLoc = Blockly.utils.Coordinate.sum(this.startXY_, delta);
+  var preventMove = this.dragTarget_ &&
+      this.dragTarget_.shouldPreventBubbleMove(this.draggingBubble_);
+  if (preventMove) {
+    var newLoc = this.startXY_;
+  } else {
+    var delta = this.pixelsToWorkspaceUnits_(currentDragDeltaXY);
+    var newLoc = Blockly.utils.Coordinate.sum(this.startXY_, delta);
+  }
   // Move the bubble to its final location.
   this.draggingBubble_.moveTo(newLoc.x, newLoc.y);
 
@@ -212,8 +218,9 @@ Blockly.BubbleDragger.prototype.endBubbleDrag = function(
     if (this.dragSurface_) {
       this.dragSurface_.clearAndHide(this.workspace_.getBubbleCanvas());
     }
-
-    this.draggingBubble_.setDragging && this.draggingBubble_.setDragging(false);
+    if (this.draggingBubble_) {
+      this.draggingBubble_.setDragging(false);
+    }
     this.fireMoveEvent_();
   }
   this.workspace_.setResizesEnabled(true);

core/drag_target.js

@@ -68,3 +68,27 @@ Blockly.DragTarget.prototype.onBlockDrop = function(_block) {
 Blockly.DragTarget.prototype.onBubbleDrop = function(_bubble) {
   // no-op
 };
+
+/**
+ * Returns whether the provided block should not be moved after being dropped
+ * on this component. If true, block will return to where it was when the drag
+ * started.
+ * @param {!Blockly.BlockSvg} _block The block.
+ * @return {boolean} Whether the block provided should be returned to drag
+ *     start.
+ */
+Blockly.DragTarget.prototype.shouldPreventBlockMove = function(_block) {
+  return false;
+};
+
+/**
+ * Returns whether the provided bubble should not be moved after being dropped
+ * on this component. If true, bubble will return to where it was when the drag
+ * started.
+ * @param {!Blockly.IBubble} _bubble The bubble.
+ * @return {boolean} Whether the bubble provided should be returned to drag
+ *    start.
+ */
+Blockly.DragTarget.prototype.shouldPreventBubbleMove = function(_bubble) {
+  return false;
+};

core/inject.js

@@ -291,7 +291,7 @@ Blockly.bumpIntoBoundsHandler_ = function(workspace) {
  *    in workspace coordinates.
  * @param {!Blockly.IBoundedElement} object The object to bump.
  * @return {boolean} True if block was bumped.
- * @private
+ * @package
  */
 Blockly.bumpObjectIntoBounds_ = function(workspace, scrollMetrics, object) {
   // Compute new top/left position for object.

core/interfaces/i_drag_target.js

@@ -58,3 +58,23 @@ Blockly.IDragTarget.prototype.onBlockDrop;
  * @param {!Blockly.IBubble} bubble The bubble.
  */
 Blockly.IDragTarget.prototype.onBubbleDrop;
+
+/**
+ * Returns whether the provided block should not be moved after being dropped
+ * on this component. If true, block will return to where it was when the drag
+ * started.
+ * @param {!Blockly.BlockSvg} block The block.
+ * @return {boolean} Whether the block provided should be returned to drag
+ *     start.
+ */
+Blockly.IDragTarget.prototype.shouldPreventBlockMove;
+
+/**
+ * Returns whether the provided bubble should not be moved after being dropped
+ * on this component. If true, bubble will return to where it was when the drag
+ * started.
+ * @param {!Blockly.IBubble} bubble The bubble.
+ * @return {boolean} Whether the bubble provided should be returned to drag
+ *    start.
+ */
+Blockly.IDragTarget.prototype.shouldPreventBubbleMove;