Broadcast message functionality (works with creating new messages, and switching back and forth between them as well). This commit includes a temporary workaround for the issue where the default broadcast message, 'message1' wasn't triggering a var_create event (filed in LLK/scratch-blocks#1258).

src/blocks/scratch3_event.js

@@ -56,14 +56,20 @@ class Scratch3EventBlocks {
     }
 
     broadcast (args, util) {
-        const broadcastOption = Cast.toString(args.BROADCAST_OPTION);
+        // TODO KARISHMA adding lookupOrCreate here temporarily (LLK/scratch-blocks#1258)
+        util.target.lookupOrCreateBroadcastMsg(args.BROADCAST_OPTION.id,
+            args.BROADCAST_OPTION.name);
+        const broadcastOption = Cast.toString(args.BROADCAST_OPTION.name);
         util.startHats('event_whenbroadcastreceived', {
             BROADCAST_OPTION: broadcastOption
         });
     }
 
     broadcastAndWait (args, util) {
-        const broadcastOption = Cast.toString(args.BROADCAST_OPTION);
+        // TODO KARISHMA adding lookupOrCreate here temporarily (LLK/scratch-blocks#1258)
+        util.target.lookupOrCreateBroadcastMsg(args.BROADCAST_OPTION.id,
+            args.BROADCAST_OPTION.name);
+        const broadcastOption = Cast.toString(args.BROADCAST_OPTION.name);
         // Have we run before, starting threads?
         if (!util.stackFrame.startedThreads) {
             // No - start hats for this broadcast.

src/engine/blocks.js

@@ -365,7 +365,8 @@ class Blocks {
         case 'field':
             // Update block value
             if (!block.fields[args.name]) return;
-            if (args.name === 'VARIABLE' || args.name === 'LIST') {
+            if (args.name === 'VARIABLE' || args.name === 'LIST' ||
+                args.name === 'BROADCAST_OPTION') {
                 // Get variable name using the id in args.value.
                 const variable = optRuntime.getEditingTarget().lookupVariableById(args.value);
                 if (variable) {

src/engine/execute.js

@@ -171,6 +171,19 @@ const execute = function (sequencer, thread) {
         if (!fields.hasOwnProperty(fieldName)) continue;
         if (fieldName === 'VARIABLE' || fieldName === 'LIST') {
             argValues[fieldName] = fields[fieldName].id;
+        } else if (fieldName === 'BROADCAST_OPTION') {
+            // TODO KARISHMA (scratch-blocks #1258) this will change when we
+            // upstream blockly issue #1395 is fixed.
+
+            // we need both the id and the name here, because
+            // this object eventually gets passed to scratch3_event.broadcast
+            // which will create the message for the first time if one with the
+            // given id doesn't exist
+            // (e.g. default broadcast message, 'message1')
+            argValues[fieldName] = {
+                id: fields[fieldName].id,
+                name: fields[fieldName].value
+            };
         } else {
             argValues[fieldName] = fields[fieldName].value;
         }

src/engine/target.js

@@ -92,6 +92,23 @@ class Target extends EventEmitter {
         return newVariable;
     }
 
+    /**
+     * Look up a broadcast message object, and create it if one doesn't exist.
+     * @param {string} id Id of the variable.
+     * @param {string} name Name of the variable.
+     * @return {!Variable} Variable object.
+     */
+    lookupOrCreateBroadcastMsg (id, name) {
+        debugger;
+        const broadcastMsg = this.lookupVariableById(id);
+        if (broadcastMsg) return broadcastMsg;
+        // No variable with this name exists - create it locally.
+        const newBroadcastMsg = new Variable(id, name,
+            Variable.BROADCAST_MESSAGE_TYPE, false);
+        this.variables[id] = newBroadcastMsg;
+        return newBroadcastMsg;
+    }
+
     /**
      * Look up a variable object.
      * Search begins for local variables; then look for globals.
@@ -134,7 +151,7 @@ class Target extends EventEmitter {
      * dictionary of variables.
      * @param {string} id Id of variable
      * @param {string} name Name of variable.
-     * @param {string} type Type of variable, '' or 'list'
+     * @param {string} type Type of variable, '', 'broadcast_msg', or 'list'
      */
     createVariable (id, name, type) {
         if (!this.variables.hasOwnProperty(id)) {

src/engine/variable.js

@@ -25,6 +25,9 @@ class Variable {
         case Variable.LIST_TYPE:
             this.value = [];
             break;
+        case Variable.BROADCAST_MESSAGE_TYPE:
+            this.value = this.name;
+            break;
         default:
             throw new Error(`Invalid variable type: ${this.type}`);
         }
@@ -51,6 +54,14 @@ class Variable {
     static get LIST_TYPE () {
         return 'list';
     }
+
+    /**
+     * Type representation for list variables.
+     * @const {string}
+     */
+    static get BROADCAST_MESSAGE_TYPE () {
+        return 'broadcast_msg';
+    }
 }
 
 module.exports = Variable;