[FIX] observer: properly handle dates

doc/component.md

@@ -255,7 +255,8 @@ At this point, the component is not yet rendered. Note that a slow `willStart` m
 interface. Therefore, some care should be made to make this method as
 fast as possible.
 
-The component rendering will take place after `willStart` is completed.
+After the `willStart` method is completed, the state will be observed with a
+new `Observer`.  Then, the component will be rendered by `QWeb`.
 
 #### `mounted()`
 

src/core/observer.ts

@@ -35,7 +35,7 @@ export class Observer {
   }
 
   observe(value: any, parent?: any): any {
-    if (value === null || typeof value !== "object") {
+    if (value === null || typeof value !== "object" || value instanceof Date) {
       // fun fact: typeof null === 'object'
       return value;
     }

tests/core/observer.test.ts

@@ -57,6 +57,25 @@ describe("observer", () => {
     });
   });
 
+  test("properly handle dates", () => {
+    const observer = new Observer();
+    const date = new Date();
+    const obj: any = observer.observe({ date });
+
+    expect(observer.revNumber(obj)).toBe(1);
+    expect(observer.deepRevNumber(obj)).toBe(1);
+    expect(observer.rev).toBe(1);
+    expect(typeof obj.date.getFullYear()).toBe('number');
+    expect(obj.date).toBe(date);
+
+    obj.date = new Date();
+
+    expect(observer.revNumber(obj)).toBe(2);
+    expect(observer.deepRevNumber(obj)).toBe(2);
+    expect(observer.rev).toBe(2);
+    expect(obj.date).not.toBe(date);
+  });
+
   test("can change values in array", () => {
     const observer = new Observer();
     const obj: any = observer.observe({ arr: [1, 2] });