[FIX] component: properly handle mounting a destroyed component

part of #685

src/component/component.ts

@@ -316,6 +316,9 @@ export class Component<Props extends {} = any, T extends Env = Env> {
         return Promise.resolve();
       }
     }
+    if (__owl__.isDestroyed) {
+      throw new Error("Cannot mount a destroyed component");
+    }
     if (__owl__.currentFiber) {
       const currentFiber = __owl__.currentFiber;
       if (currentFiber.target === target && currentFiber.position === position) {

tests/component/component.test.ts

@@ -1,16 +1,16 @@
 import { Component, Env } from "../../src/component/component";
+import { EventBus } from "../../src/core/event_bus";
+import { useRef, useState } from "../../src/hooks";
 import { QWeb } from "../../src/qweb/qweb";
 import { xml } from "../../src/tags";
-import { useState, useRef } from "../../src/hooks";
-import { EventBus } from "../../src/core/event_bus";
 import {
+  editInput,
   makeDeferred,
-  makeTestFixture,
   makeTestEnv,
+  makeTestFixture,
   nextMicroTick,
   nextTick,
   normalize,
-  editInput,
 } from "../helpers";
 
 //------------------------------------------------------------------------------

tests/component/un_mounting.test.ts

@@ -2,6 +2,7 @@ import { Component, Env } from "../../src/component/component";
 import { useState } from "../../src/hooks";
 import { xml } from "../../src/tags";
 import { makeDeferred, makeTestEnv, makeTestFixture, nextTick, nextMicroTick } from "../helpers";
+import { scheduler } from "../../src/component/scheduler";
 
 //------------------------------------------------------------------------------
 // Setup and helpers
@@ -490,4 +491,22 @@ describe("unmounting and remounting", () => {
     expect(steps).toEqual(["1 resolved", "2 resolved"]);
     expect(fixture.innerHTML).toBe("<div>Hey</div>");
   });
+
+  test("mounting a destroyed widget", async () => {
+    class MyWidget extends Component {
+      static template = xml`<div>Hey</div>`;
+    }
+    const w = new MyWidget();
+    w.destroy(); // because, why not
+
+    let error;
+    try {
+      await w.mount(fixture);
+    } catch (e) {
+      error = e;
+    }
+    expect(scheduler.tasks.length).toBe(0);
+    expect(error).toBeDefined();
+    expect(error.message).toBe("Cannot mount a destroyed component");
+  });
 });