add warning when rendering outside of render fn for templates

src/platform/web/ui/general/TemplateView.js

@@ -68,6 +68,7 @@ export class TemplateView extends BaseUpdateView {
 
     mount(options) {
         const builder = new TemplateBuilder(this);
+        try {
             if (this._render) {
                 this._root = this._render(builder, this._value);
             } else if (this.render) {   // overriden in subclass
@@ -75,6 +76,9 @@ export class TemplateView extends BaseUpdateView {
             } else {
                 throw new Error("no render function passed in, or overriden in subclass");
             }
+        } finally {
+            builder.close();
+        }
         // takes care of update being called when needed
         super.mount(options);
         this._attach();
@@ -145,6 +149,18 @@ export class TemplateView extends BaseUpdateView {
 class TemplateBuilder {
     constructor(templateView) {
         this._templateView = templateView;
+        this._closed = false;
+    }
+
+    close() {
+        this._closed = true;
+    }
+
+    _addBinding(fn) {
+        if (this._closed) {
+            console.trace("Adding a binding after render will likely cause memory leaks");
+        }
+        this._templateView._addBinding(fn);
     }
 
     get _value() {
@@ -164,7 +180,7 @@ class TemplateBuilder {
                 setAttribute(node, name, newValue);
             }
         };
-        this._templateView._addBinding(binding);
+        this._addBinding(binding);
         binding();
     }
 
@@ -184,7 +200,7 @@ class TemplateBuilder {
             }
         };
 
-        this._templateView._addBinding(binding);
+        this._addBinding(binding);
         return node;
     }
 
@@ -240,7 +256,7 @@ class TemplateBuilder {
                 node = newNode;
             }
         };
-        this._templateView._addBinding(binding);
+        this._addBinding(binding);
         return node;
     }