[FIX] component: make sure props are validated in all cases

closes #379

src/component/component.ts

@@ -134,6 +134,9 @@ export class Component<T extends Env, Props extends {}> {
     //   Con: this is not really safe
     //   Pro: but creating component (by a template) is always unsafe anyway
     this.props = <Props>props || <Props>{};
+    if (QWeb.dev) {
+      QWeb.utils.validateProps(this.constructor, this.props);
+    }
     let id: number = nextId++;
     let p: Component<T, any> | null = null;
     if (parent instanceof Component) {
@@ -142,11 +145,6 @@ export class Component<T extends Env, Props extends {}> {
       parent.__owl__.children[id] = this;
     } else {
       this.env = parent;
-      if (QWeb.dev) {
-        // we only validate props for root widgets here.  "Regular" widget
-        // props are validated by the t-component directive
-        QWeb.utils.validateProps(this.constructor, this.props);
-      }
       this.env.qweb.on("update", this, () => {
         if (this.__owl__.isMounted) {
           this.render(true);

src/component/props_validation.ts

@@ -21,7 +21,7 @@ QWeb.utils.validateProps = function(Widget, props: Object) {
         // optional prop
         break;
       }
-      if (!props[propName]) {
+      if (!(propName in props)) {
         throw new Error(`Missing props '${propsDef[i]}' (component '${Widget.name}')`);
       }
     }

tests/component/props_validation.test.ts

@@ -322,6 +322,28 @@ describe("props validation", () => {
       QWeb.utils.validateProps(TestWidget, { message: null });
     }).toThrow();
   });
+
+  test("can set default required boolean values", async () => {
+    class TestWidget extends Widget {
+      static props = ["p"];
+      static template = xml`<span><t t-if="props.p">hey</t></span>`;
+    }
+
+    class App extends Widget {
+      static template = xml`<div><TestWidget/></div>`;
+      static components = { TestWidget };
+    }
+
+    const w = new App(env, {});
+    let error;
+    try {
+      await w.mount(fixture);
+    } catch (e) {
+      error = e;
+    }
+    expect(error).toBeDefined();
+    expect(error.message).toBe("Missing props 'p' (component 'TestWidget')");
+  });
 });
 
 describe("default props", () => {