From 2523da53320c770564af8336ae610832012fcca8 Mon Sep 17 00:00:00 2001
From: alschmiedt <aschmiedt@google.com>
Date: Thu, 17 Sep 2020 16:45:24 -0700
Subject: [PATCH] Fixes blocks flying when mutator is open (#4289)

---
 core/mutator.js | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/core/mutator.js b/core/mutator.js
index 462a78b04..3e4ba64cc 100644
--- a/core/mutator.js
+++ b/core/mutator.js
@@ -401,15 +401,28 @@ Blockly.Mutator.prototype.workspaceChanged_ = function(e) {
     var block = this.block_;
     var oldMutationDom = block.mutationToDom();
     var oldMutation = oldMutationDom && Blockly.Xml.domToText(oldMutationDom);
+
+    // Switch off rendering while the source block is rebuilt.
+    var savedRendered = block.rendered;
+    // TODO(#4288): We should not be setting the rendered property to false.
+    block.rendered = false;
+
     // Allow the source block to rebuild itself.
     block.compose(this.rootBlock_);
+    // Restore rendering and show the changes.
+    block.rendered = savedRendered;
+    // Mutation may have added some elements that need initializing.
     block.initSvg();
-    block.render();
 
     if ((/** @type {!Blockly.WorkspaceSvg} */ (Blockly.getMainWorkspace()))
         .keyboardAccessibilityMode) {
       Blockly.navigation.moveCursorOnBlockMutation(block);
     }
+
+    if (block.rendered) {
+      block.render();
+    }
+
     var newMutationDom = block.mutationToDom();
     var newMutation = newMutationDom && Blockly.Xml.domToText(newMutationDom);
     if (oldMutation != newMutation) {