Add programmatically setting shadows (#3902)

* Add programmatically setting shadows

core/connection.js

@@ -108,7 +108,7 @@ Blockly.Connection.prototype.connect_ = function(childConnection) {
     var orphanBlock = parentConnection.targetBlock();
     var shadowDom = parentConnection.getShadowDom();
     // Temporarily set the shadow DOM to null so it does not respawn.
-    parentConnection.setShadowDom(null);
+    parentConnection.shadowDom_ = null;
     // Displaced shadow blocks dissolve rather than reattaching or bumping.
     if (orphanBlock.isShadow()) {
       // Save the shadow block so that field values are preserved.
@@ -175,7 +175,7 @@ Blockly.Connection.prototype.connect_ = function(childConnection) {
       }
     }
     // Restore the shadow DOM.
-    parentConnection.setShadowDom(shadowDom);
+    parentConnection.shadowDom_ = shadowDom;
   }
 
   var event;
@@ -200,12 +200,11 @@ Blockly.Connection.prototype.dispose = function() {
 
   // isConnected returns true for shadows and non-shadows.
   if (this.isConnected()) {
+    // Destroy the attached shadow block & its children (if it exists).
     this.setShadowDom(null);
+
     var targetBlock = this.targetBlock();
-    if (targetBlock.isShadow()) {
-      // Destroy the attached shadow block & its children.
-      targetBlock.dispose(false);
-    } else {
+    if (targetBlock) {
       // Disconnect the attached normal block.
       targetBlock.unplug();
     }
@@ -672,15 +671,22 @@ Blockly.Connection.prototype.getCheck = function() {
 };
 
 /**
- * Change a connection's shadow block.
+ * Changes the connection's shadow block.
  * @param {Element} shadow DOM representation of a block or null.
  */
 Blockly.Connection.prototype.setShadowDom = function(shadow) {
   this.shadowDom_ = shadow;
+  var target = this.targetBlock();
+  if (!target) {
+    this.respawnShadow_();
+  } else if (target.isShadow()) {
+    // The disconnect from dispose will automatically generate the new shadow.
+    target.dispose(false);
+  }
 };
 
 /**
- * Return a connection's shadow block.
+ * Returns the xml representation of the connection's shadow block.
  * @return {Element} Shadow DOM representation of a block or null.
  */
 Blockly.Connection.prototype.getShadowDom = function() {

core/input.js

@@ -231,6 +231,30 @@ Blockly.Input.prototype.setAlign = function(align) {
   return this;
 };
 
+/**
+ * Changes the connection's shadow block.
+ * @param {Element} shadow DOM representation of a block or null.
+ * @return {Blockly.Input} The input being modified (to allow chaining).
+ */
+Blockly.Input.prototype.setShadowDom = function(shadow) {
+  if (!this.connection) {
+    throw Error('This input does not have a connection.');
+  }
+  this.connection.setShadowDom(shadow);
+  return this;
+};
+
+/**
+ * Returns the xml representation of the connection's shadow block.
+ * @return {Element} Shadow DOM representation of a block or null.
+ */
+Blockly.Input.prototype.getShadowDom = function() {
+  if (!this.connection) {
+    throw Error('This input does not have a connection.');
+  }
+  return this.connection.getShadowDom();
+};
+
 /**
  * Initialize the fields on this input.
  */

core/xml.js

@@ -661,10 +661,6 @@ Blockly.Xml.domToBlockHeadless_ = function(xmlBlock, workspace) {
         }
       }
     }
-    // Use the shadow block if there is no child block.
-    if (!childBlockElement && childShadowElement) {
-      childBlockElement = childShadowElement;
-    }
 
     var name = xmlChild.getAttribute('name');
     var xmlChildElement = /** @type {!Element} */ (xmlChild);
@@ -719,9 +715,6 @@ Blockly.Xml.domToBlockHeadless_ = function(xmlBlock, workspace) {
                        prototypeName);
           break;
         }
-        if (childShadowElement) {
-          input.connection.setShadowDom(childShadowElement);
-        }
         if (childBlockElement) {
           blockChild = Blockly.Xml.domToBlockHeadless_(childBlockElement,
               workspace);
@@ -734,11 +727,12 @@ Blockly.Xml.domToBlockHeadless_ = function(xmlBlock, workspace) {
                 'Child block does not have output or previous statement.');
           }
         }
+        // Set shadow after so we don't create a shadow we delete immediately.
+        if (childShadowElement) {
+          input.connection.setShadowDom(childShadowElement);
+        }
         break;
       case 'next':
-        if (childShadowElement && block.nextConnection) {
-          block.nextConnection.setShadowDom(childShadowElement);
-        }
         if (childBlockElement) {
           if (!block.nextConnection) {
             throw TypeError('Next statement does not exist.');
@@ -754,6 +748,10 @@ Blockly.Xml.domToBlockHeadless_ = function(xmlBlock, workspace) {
           }
           block.nextConnection.connect(blockChild.previousConnection);
         }
+        // Set shadow after so we don't create a shadow we delete immediately.
+        if (childShadowElement && block.nextConnection) {
+          block.nextConnection.setShadowDom(childShadowElement);
+        }
         break;
       default:
         // Unknown tag; ignore.  Same principle as HTML parsers.