From a8bfc3854562cba1b95d561faa4765872a615347 Mon Sep 17 00:00:00 2001
From: Sean Lip <sll@google.com>
Date: Fri, 1 Jul 2016 15:17:32 -0700
Subject: [PATCH] Forbid any ancestor of the block containing the marked
 connection from being moved to said connection.

---
 accessible/clipboard.service.js | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/accessible/clipboard.service.js b/accessible/clipboard.service.js
index 43c93b278..41e5bdb14 100644
--- a/accessible/clipboard.service.js
+++ b/accessible/clipboard.service.js
@@ -46,13 +46,20 @@ blocklyApp.ClipboardService = ng.core
           this.areConnectionsCompatible_(connection, nextConnection));
     },
     isMovableToMarkedConnection: function(block) {
-      // It should not be possible to move a block to one of its own
-      // connections.
-      if (this.markedConnection_ &&
-          this.markedConnection_.sourceBlock_.id == block.id) {
+      // It should not be possible to move any ancestor of the block containing
+      // the marked spot to the marked spot.
+      if (!this.markedConnection_) {
         return false;
       }
 
+      var markedSpotAncestorBlock = this.markedConnection_.getSourceBlock();
+      while (markedSpotAncestorBlock) {
+        if (markedSpotAncestorBlock.id == block.id) {
+          return false;
+        }
+        markedSpotAncestorBlock = markedSpotAncestorBlock.getParent();
+      }
+
       return this.canBeCopiedToMarkedConnection(block);
     },
     canBeCopiedToMarkedConnection: function(block) {