automatically remove orphaned variable watchers

HISTORY.md

@@ -7,12 +7,16 @@
 * **Translation Updates:**
 
 ## 5.4.4:
-* **Notable Fix**
+* **Notable Fixes**
     * fixed strings library format
+    * automatically remove orphaned variable watchers
+
+### 2020-01-11
+* objects: automatically remove orphaned variable watchers
+* prepared patch
 
 ### 2020-01-10
 * fixed strings library format
-* prepared patch
 
 ## 5.4.3:
 * **Notable Fix**

snap.html

@@ -8,8 +8,8 @@
         <script type="text/javascript" src="src/widgets.js?version=2020-01-03"></script>
         <script type="text/javascript" src="src/blocks.js?version=2020-01-06"></script>
         <script type="text/javascript" src="src/threads.js?version=2019-12-19"></script>
-        <script type="text/javascript" src="src/objects.js?version=2020-01-03"></script>
-        <script type="text/javascript" src="src/gui.js?version=2020-01-10"></script>
+        <script type="text/javascript" src="src/objects.js?version=2020-01-11"></script>
+        <script type="text/javascript" src="src/gui.js?version=2020-01-11"></script>
         <script type="text/javascript" src="src/paint.js?version=2019-06-27"></script>
         <script type="text/javascript" src="src/lists.js?version=2019-12-08"></script>
         <script type="text/javascript" src="src/byob.js?version=2020-01-03"></script>

src/gui.js

@@ -78,7 +78,7 @@ Animation, BoxMorph, BlockEditorMorph, BlockDialogMorph*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.gui = '2020-January-10';
+modules.gui = '2020-January-11';
 
 // Declarations
 

src/objects.js

@@ -84,7 +84,7 @@ BlockEditorMorph, BlockDialogMorph, PrototypeHatBlockMorph,  BooleanSlotMorph,
 localize, TableMorph, TableFrameMorph, normalizeCanvas, VectorPaintEditorMorph,
 HandleMorph, AlignmentMorph, Process, XML_Element, WorldMap, copyCanvas*/
 
-modules.objects = '2020-January-03';
+modules.objects = '2020-January-11';
 
 var SpriteMorph;
 var StageMorph;
@@ -11282,9 +11282,18 @@ WatcherMorph.prototype.update = function () {
                 newValue = Math.round(newValue * 1000000000) / 1000000000;
             }
         }
+        if (newValue === undefined) {
+            // console.log('removing watcher for', this.labelText);
+            this.destroy();
+            return;
+        }
         if (newValue !== this.currentValue ||
                 isInherited !== this.isGhosted ||
-                (newValue.version && (newValue.version !== this.version))) {
+                (!isNil(newValue) &&
+                    newValue.version &&
+                    (newValue.version !== this.version)
+                )
+        ) {
             this.changed();
             this.cellMorph.contents = newValue;
             this.isGhosted = isInherited;