[ADD] runtime/utils: optional validation to EventBus

Currently the event bus allows sending and listening to arbitrary
events, I got got by that when I pushed a fix using `addEventListener`
on a bus across an events renaming, and on the other side the fix did
nothing anymore. Entirely my fault, but if the list of events sent on
a bus is known and documented (e.g. a jsdoc has `@emits` tags) it
would make sense for both the listening and the dispatching to also be
validated.

This proposal performs validation only when the eventbus is created:

- in dev mode (which also requires being in a component context)
- if an iterable of events is passed to the ctor

The dev-mode check might be overkill but it seems like a good idea at
least for an initial version, as the validation does have a cost
however low, and validation errors can occur essentially anywhere.

doc/reference/props.md

@@ -320,6 +320,28 @@ class ComponentB extends owl.Component {
 
 Note: the props validation code is done by using the [validate utility function](utils.md#validate).
 
+### `slots` prop
+
+If a component that uses [slots](slots.md) also lists or validates its props, then
+you will have to explicitely allow the `slots` prop (with an `Object` type), or
+allow extra props using the `*` notation mentioned above. This is because slots
+are provided to a component [as props](slots.md#slots-and-props).
+
+For example:
+
+```js
+class MyComponent extends Component {
+  static props = [someProp, slots?];
+}
+
+class MyComponentWithValidation extends Component {
+  static props = {
+    someProp: {type: Number, optional: true},
+    slots : {type: Object, optional: true},
+  }
+}
+```
+
 ## Good Practices
 
 A `props` object is a collection of values that come from the parent. As such,

src/runtime/utils.ts

@@ -1,4 +1,5 @@
 import { OwlError } from "../common/owl_error";
+import { ComponentNode, getCurrent } from "./component_node";
 export type Callback = () => void;
 
 /**
@@ -81,10 +82,52 @@ export function validateTarget(target: HTMLElement | ShadowRoot) {
 }
 
 export class EventBus extends EventTarget {
+  constructor(events?: string[]) {
+    if (events) {
+      let node: ComponentNode | null = null;
+      try {
+        node = getCurrent();
+      } catch {}
+      if (node?.app?.dev) {
+        return new DebugEventBus(events);
+      }
+    }
+    super();
+  }
   trigger(name: string, payload?: any) {
     this.dispatchEvent(new CustomEvent(name, { detail: payload }));
   }
 }
+class DebugEventBus extends EventBus {
+  private events: Set<string>;
+  constructor(events: string[]) {
+    super();
+    this.events = new Set(events);
+  }
+  addEventListener(
+    type: string,
+    listener: EventListenerOrEventListenerObject | null,
+    options?: boolean | AddEventListenerOptions
+  ): void {
+    if (!this.events.has(type)) {
+      throw new OwlError(`EventBus: subscribing to unknown event '${type}'`);
+    }
+    super.addEventListener(type, listener, options);
+  }
+  trigger(name: string, payload?: any) {
+    if (!this.events.has(name)) {
+      throw new OwlError(`EventBus: triggering unknown event '${name}'`);
+    }
+    super.trigger(name, payload);
+  }
+
+  dispatchEvent(event: Event): boolean {
+    if (!this.events.has(event.type)) {
+      throw new OwlError(`EventBus: dispatching unknown event '${event.type}'`);
+    }
+    return super.dispatchEvent(event);
+  }
+}
 
 export function whenReady(fn?: any): Promise<void> {
   return new Promise(function (resolve) {

tests/utils.test.ts

@@ -1,5 +1,7 @@
 import { batched, EventBus, htmlEscape, markup } from "../src/runtime/utils";
-import { nextMicroTick } from "./helpers";
+import { makeTestFixture, nextMicroTick } from "./helpers";
+import { getCurrent } from "../src/runtime/component_node";
+import { Component, mount, xml } from "../src";
 
 describe("event bus behaviour", () => {
   test("can subscribe and be notified", () => {
@@ -33,6 +35,66 @@ describe("event bus behaviour", () => {
     bus.addEventListener("event", (ev: any) => expect(ev.detail).toBe("hello world"));
     bus.trigger("event", "hello world");
   });
+
+  test("events are not validated if the bus is created outside of dev mode", async () => {
+    let bus_empty: EventBus | null = null;
+    class Root extends Component {
+      static template = xml`<div/>`;
+
+      setup() {
+        getCurrent(); // checks that we're in a component context
+
+        bus_empty = new EventBus([]);
+      }
+    }
+    await mount(Root, makeTestFixture());
+
+    bus_empty!.addEventListener("a", () => {});
+    bus_empty!.trigger("a");
+    bus_empty!.dispatchEvent(new CustomEvent("a"));
+  });
+  test("events are validated if the bus is created in dev mode & events are provided", async () => {
+    let bus: EventBus | null = null;
+    let bus_empty: EventBus | null = null;
+    let bbus_no_validation: EventBus | null = null;
+    class Root extends Component {
+      static template = xml`<div/>`;
+
+      setup() {
+        getCurrent(); // checks that we're in a component context
+
+        bus = new EventBus(["a", "b"]);
+        bus_empty = new EventBus([]);
+        bbus_no_validation = new EventBus();
+      }
+    }
+
+    await mount(Root, makeTestFixture(), { test: true });
+
+    bbus_no_validation!.addEventListener("c", () => {});
+    bbus_no_validation!.trigger("c");
+    bbus_no_validation!.dispatchEvent(new CustomEvent("c"));
+
+    bus!.addEventListener("a", () => {});
+    bus!.trigger("a");
+    bus!.dispatchEvent(new CustomEvent("a"));
+
+    expect(() => bus!.addEventListener("c", () => {})).toThrow(
+      "EventBus: subscribing to unknown event 'c'"
+    );
+    expect(() => bus!.trigger("c")).toThrow("EventBus: triggering unknown event 'c'");
+    expect(() => bus!.dispatchEvent(new CustomEvent("c"))).toThrow(
+      "EventBus: dispatching unknown event 'c'"
+    );
+
+    expect(() => bus_empty!.addEventListener("a", () => {})).toThrow(
+      "EventBus: subscribing to unknown event 'a'"
+    );
+    expect(() => bus_empty!.trigger("a")).toThrow("EventBus: triggering unknown event 'a'");
+    expect(() => bus_empty!.dispatchEvent(new CustomEvent("a"))).toThrow(
+      "EventBus: dispatching unknown event 'a'"
+    );
+  });
 });
 
 describe("batched", () => {