[FIX] runtime: properly handle error caused in mounted hook

src/runtime/scheduler.ts

@@ -93,7 +93,14 @@ export class Scheduler {
       if (!hasError) {
         fiber.complete();
       }
-      this.tasks.delete(fiber);
+      // at this point, the fiber should have been applied to the DOM, so we can
+      // remove it from the task list. If it is not the case, it means that there
+      // was an error and an error handler triggered a new rendering that recycled
+      // the fiber, so in that case, we actually want to keep the fiber around,
+      // otherwise it will just be ignored.
+      if (fiber.appliedToDom) {
+        this.tasks.delete(fiber);
+      }
     }
   }
 }

tests/components/__snapshots__/error_handling.test.ts.snap

@@ -320,6 +320,50 @@ exports[`can catch errors can catch an error in a component render function 3`]
 }"
 `;
 
+exports[`can catch errors can catch an error in onmounted 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const comp1 = app.createComponent(null, false, false, false, []);
+
+  return function template(ctx, node, key = \\"\\") {
+    let b2, b3;
+    b2 = text(\`Main\`);
+    if (ctx['state'].ok) {
+      const Comp1 = ctx['component'];
+      b3 = toggler(Comp1, comp1({}, (Comp1).name + key + \`__1\`, node, this, Comp1));
+    }
+    return multi([b2, b3]);
+  }
+}"
+`;
+
+exports[`can catch errors can catch an error in onmounted 3`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+
+  let block1 = createBlock(\`<div>Error!!!</div>\`);
+
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;
+
+exports[`can catch errors can catch an error in onmounted 4`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+
+  let block1 = createBlock(\`<div>perfect</div>\`);
+
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;
+
 exports[`can catch errors can catch an error in the constructor call of a component render function 1`] = `
 "function anonymous(app, bdom, helpers
 ) {

tests/components/error_handling.test.ts

@@ -564,6 +564,82 @@ describe("can catch errors", () => {
     expect(mockConsoleWarn).toBeCalledTimes(0);
   });
 
+  test("can catch an error in onmounted", async () => {
+    class ErrorComponent extends Component {
+      static template = xml`<div>Error!!!</div>`;
+      setup() {
+        useLogLifecycle();
+        onMounted(() => {
+          throw new Error("error");
+        });
+      }
+    }
+    class PerfectComponent extends Component {
+      static template = xml`<div>perfect</div>`;
+      setup() {
+        useLogLifecycle();
+      }
+    }
+    class Main extends Component {
+      static template = xml`Main<t t-if="state.ok" t-component="component"/>`;
+      component: any;
+      state: any;
+      setup() {
+        this.state = useState({ ok: false });
+        useLogLifecycle();
+        this.component = ErrorComponent;
+        onError(() => {
+          this.component = PerfectComponent;
+          this.render();
+        });
+      }
+    }
+
+    const app = await mount(Main, fixture);
+    expect(steps.splice(0)).toMatchInlineSnapshot(`
+      Array [
+        "Main:setup",
+        "Main:willStart",
+        "Main:willRender",
+        "Main:rendered",
+        "Main:mounted",
+      ]
+    `);
+    expect(fixture.innerHTML).toBe("Main");
+    (app as any).state.ok = true;
+    await nextTick();
+    expect(fixture.innerHTML).toBe("Main<div>Error!!!</div>");
+    expect(steps.splice(0)).toMatchInlineSnapshot(`
+      Array [
+        "Main:willRender",
+        "ErrorComponent:setup",
+        "ErrorComponent:willStart",
+        "Main:rendered",
+        "ErrorComponent:willRender",
+        "ErrorComponent:rendered",
+        "Main:willPatch",
+        "ErrorComponent:mounted",
+        "Main:willRender",
+        "PerfectComponent:setup",
+        "PerfectComponent:willStart",
+        "Main:rendered",
+      ]
+    `);
+    await nextTick();
+    expect(steps.splice(0)).toMatchInlineSnapshot(`
+      Array [
+        "PerfectComponent:willRender",
+        "PerfectComponent:rendered",
+        "Main:willPatch",
+        "ErrorComponent:willUnmount",
+        "ErrorComponent:willDestroy",
+        "PerfectComponent:mounted",
+        "Main:patched",
+      ]
+    `);
+    expect(fixture.innerHTML).toBe("Main<div>perfect</div>");
+  });
+
   test("calling a hook outside setup should crash", async () => {
     class Root extends Component {
       static template = xml`<t t-esc="state.value"/>`;