From 5938c6df3bc400918e882b70c1249590db6bb2d7 Mon Sep 17 00:00:00 2001
From: Rachel Fenichel <fenichel@google.com>
Date: Fri, 30 Nov 2018 14:34:14 -0800
Subject: [PATCH 1/3] Fix #2131

---
 core/connection.js | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/core/connection.js b/core/connection.js
index 11d26cbd4..990be154c 100644
--- a/core/connection.js
+++ b/core/connection.js
@@ -360,12 +360,7 @@ Blockly.Connection.prototype.canConnectToPrevious_ = function(candidate) {
   var isFirstStatementConnection = this == firstStatementConnection;
   var isNextConnection = this == this.sourceBlock_.nextConnection;
 
-  // Complex blocks with no previous connection will not be allowed to connect
-  // mid-stack.
-  var sourceHasPreviousConn = this.sourceBlock_.previousConnection != null;
-
-  if (isNextConnection ||
-      (isFirstStatementConnection && !sourceHasPreviousConn)) {
+  if (isNextConnection || isFirstStatementConnection) {
     // If the candidate is the first connection in a stack, we can connect.
     if (!candidate.targetConnection) {
       return true;

From b606bc5ec6caa399eaa274b33383e5b05b68b3a7 Mon Sep 17 00:00:00 2001
From: Rachel Fenichel <fenichel@google.com>
Date: Fri, 30 Nov 2018 14:36:37 -0800
Subject: [PATCH 2/3] Don't distinguish between first statement connection and
 others

---
 core/connection.js | 34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

diff --git a/core/connection.js b/core/connection.js
index 990be154c..6e978dedc 100644
--- a/core/connection.js
+++ b/core/connection.js
@@ -355,29 +355,19 @@ Blockly.Connection.prototype.canConnectToPrevious_ = function(candidate) {
     return false;
   }
 
-  var firstStatementConnection =
-      this.sourceBlock_.getFirstStatementConnection();
-  var isFirstStatementConnection = this == firstStatementConnection;
-  var isNextConnection = this == this.sourceBlock_.nextConnection;
-
-  if (isNextConnection || isFirstStatementConnection) {
-    // If the candidate is the first connection in a stack, we can connect.
-    if (!candidate.targetConnection) {
-      return true;
-    }
-
-    var targetBlock = candidate.targetBlock();
-    // If it is connected to a real block, game over.
-    if (!targetBlock.isInsertionMarker()) {
-      return false;
-    }
-    // If it's connected to an insertion marker but that insertion marker
-    // is the first block in a stack, it's still fine.  If that insertion
-    // marker is in the middle of a stack, it won't work.
-    return !targetBlock.getPreviousBlock();
+  if (!candidate.targetConnection) {
+    return true;
   }
-  console.warn('Returning false by default from canConnectToPrevious_.');
-  return false;
+
+  var targetBlock = candidate.targetBlock();
+  // If it is connected to a real block, game over.
+  if (!targetBlock.isInsertionMarker()) {
+    return false;
+  }
+  // If it's connected to an insertion marker but that insertion marker
+  // is the first block in a stack, it's still fine.  If that insertion
+  // marker is in the middle of a stack, it won't work.
+  return !targetBlock.getPreviousBlock();
 };
 
 /**

From 1553096b480e3769bb7dc29b7476960aaeac1b84 Mon Sep 17 00:00:00 2001
From: Rachel Fenichel <fenichel@google.com>
Date: Fri, 30 Nov 2018 14:46:09 -0800
Subject: [PATCH 3/3] Check if both sides of a potential connection match, not
 just one

---
 core/insertion_marker_manager.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/core/insertion_marker_manager.js b/core/insertion_marker_manager.js
index fb2fbd81b..f94677c8d 100644
--- a/core/insertion_marker_manager.js
+++ b/core/insertion_marker_manager.js
@@ -335,7 +335,8 @@ Blockly.InsertionMarkerManager.prototype.shouldUpdatePreviews_ = function(
     // Decide whether the new connection has higher priority.
     if (this.localConnection_ && this.closestConnection_) {
       // The connection was the same as the current connection.
-      if (this.closestConnection_ == candidateClosest) {
+      if (this.closestConnection_ == candidateClosest &&
+          this.localConnection_ == candidateLocal) {
         return false;
       }
       var xDiff = this.localConnection_.x_ + dxy.x - this.closestConnection_.x_;