big change: shallow render

With this commit, component only render child
components if they have different props (shallow
equality). Otherwise, we trust the reactivity
system to make sure that all impacted components
are updated

tests/components/rendering.test.ts

@@ -0,0 +1,49 @@
+import { Component, mount, onRendered, useState } from "../../src";
+import { xml } from "../../src/tags";
+import { makeTestFixture, snapshotEverything, nextTick } from "../helpers";
+
+let fixture: HTMLElement;
+
+snapshotEverything();
+
+beforeEach(() => {
+  fixture = makeTestFixture();
+});
+
+describe("rendering semantics", () => {
+  test("can render a parent without rendering child", async () => {
+    let childN = 0;
+    let parentN = 0;
+    class Child extends Component {
+      static template = xml`child`;
+      setup() {
+        onRendered(() => childN++);
+      }
+    }
+
+    class Parent extends Component {
+      static template = xml`
+        <t t-esc="state.value"/>
+        <Child/>
+      `;
+      static components = { Child };
+
+      state = useState({ value: "A" });
+      setup() {
+        onRendered(() => parentN++);
+      }
+    }
+
+    const parent = await mount(Parent, fixture);
+
+    expect(fixture.innerHTML).toBe("Achild");
+    expect(parentN).toBe(1);
+    expect(childN).toBe(1);
+
+    parent.state.value = "B";
+    await nextTick();
+    expect(fixture.innerHTML).toBe("Bchild");
+    expect(parentN).toBe(2);
+    expect(childN).toBe(1);
+  });
+});