prevent issue when widget is toggled

README.md

@@ -182,3 +182,6 @@ We have 3 main folders and 3 main files:
 
   - check if it is possible to remove parent reference in widget
   - default implementation of propsUpdated?
+
+- **Rendering** think about batching all patching updates in a
+  nextanimationframe

web/static/src/ts/core/Widget.ts

@@ -26,6 +26,7 @@ interface Meta<T extends WEnv> {
   parent: Widget<T> | null;
   children: { [key: number]: Widget<T> };
   // children mapping: from templateID to widgetID
+  // should it be a map number => Widget?
   cmap: { [key: number]: number };
 }
 

web/static/src/ts/core/qweb_vdom.ts

@@ -715,16 +715,16 @@ const widgetDirective: Directive = {
     ctx.addLine(`let _${dummyID}_index = c${ctx.parentNode}.length;`);
     ctx.addLine(`c${ctx.parentNode}.push(_${dummyID});`);
     ctx.addLine(`let def${defID};`);
+    ctx.addLine(
+      `let w${widgetID} = ${widgetID} in context.__widget__.cmap ? context.__widget__.children[context.__widget__.cmap[${widgetID}]] : false;`
+    );
 
-    ctx.addLine(`if (${widgetID} in context.__widget__.cmap) {`);
+    ctx.addLine(`if (w${widgetID}) {`);
     ctx.indent();
     ctx.addLine(
-      `let curWidget = context.__widget__.children[context.__widget__.cmap[${widgetID}]]`
+      `def${defID} = w${widgetID}.updateProps(${props}).then(()=>{vnode=w${widgetID}.__widget__.vnode;c${
-    );
-    ctx.addLine(
-      `def${defID} = curWidget.updateProps(${props}).then(()=>{vnode=curWidget.__widget__.vnode;c${
         ctx.parentNode
-      }[_${dummyID}_index]=vnode;vnode.data.hook = {remove(){curWidget.destroy()}}});`
+      }[_${dummyID}_index]=vnode;vnode.data.hook = {remove(){w${widgetID}.destroy()}}});`
     );
     ctx.dedent();
     ctx.addLine("} else {");
@@ -734,7 +734,7 @@ const widgetDirective: Directive = {
       `let _${widgetID} = new context.widgets['${value}'](owner, ${props});`
     );
     ctx.addLine(
-      `context.__widget__.cmap[${widgetID}] = _${widgetID}.__widget__.id`
+      `context.__widget__.cmap[${widgetID}] = _${widgetID}.__widget__.id;`
     );
     ctx.addLine(
       `def${defID} = _${widgetID}._start().then(() => _${widgetID}._render()).then(vnode=>{c${

web/static/tests/core/widget.test.ts

@@ -535,6 +535,30 @@ describe("composition", () => {
       "<div><div>1<button>Inc</button></div></div>"
     );
   });
+
+  test("sub widgets are destroyed if no longer in dom, then recreated", async () => {
+    class ParentWidget extends Widget<WEnv> {
+      name = "a";
+      state = { ok: true };
+      template = `
+          <div><t t-if="state.ok"><t t-widget="counter"/></t></div>`;
+      widgets = { counter: Counter };
+    }
+    const widget = new ParentWidget(env);
+    await widget.mount(fixture);
+    const button = fixture.getElementsByTagName("button")[0];
+    await button.click();
+    await nextTick();
+    expect(fixture.innerHTML).toBe(
+      "<div><div>1<button>Inc</button></div></div>"
+    );
+    await widget.updateState({ ok: false });
+    expect(fixture.innerHTML).toBe("<div></div>");
+    await widget.updateState({ ok: true });
+    expect(fixture.innerHTML).toBe(
+      "<div><div>0<button>Inc</button></div></div>"
+    );
+  });
 });
 
 describe("props evaluation (with t-props directive)", () => {