[IMP] component/tags: add inline css tag

This add an important feature: defining completely standalone owl
components, with the template/style and javascript code together.

closes #284

tests/component/styles.test.ts

@@ -0,0 +1,132 @@
+import { Component, Env } from "../../src/component/component";
+import { xml, css } from "../../src/tags";
+import { makeTestFixture, makeTestEnv } from "../helpers";
+
+//------------------------------------------------------------------------------
+// Setup and helpers
+//------------------------------------------------------------------------------
+
+// We create before each test:
+// - fixture: a div, appended to the DOM, intended to be the target of dom
+//   manipulations.  Note that it is removed after each test.
+// - env: an Env, necessary to create new components
+
+let fixture: HTMLElement;
+let env: Env;
+
+beforeEach(() => {
+  fixture = makeTestFixture();
+  env = makeTestEnv();
+  Component.env = env;
+  document.head.innerHTML = "";
+});
+
+afterEach(() => {
+  fixture.remove();
+});
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+describe("styles and component", () => {
+  test("can define an inline stylesheet", async () => {
+    class App extends Component<any, any> {
+      static template = xml`<div class="app">text</div>`;
+      static style = css`
+        .app {
+          color: red;
+        }
+      `;
+    }
+    expect(document.head.innerHTML).toBe("");
+    const app = new App();
+
+    expect(document.head.innerHTML).toBe(`<style component=\"App\">.app {
+  color: red;
+}</style>`);
+
+    await app.mount(fixture);
+    const style = getComputedStyle(app.el!);
+    expect(style.color).toBe("red");
+    expect(fixture.innerHTML).toBe('<div class="app">text</div>');
+  });
+
+  test("inherited components properly apply css", async () => {
+    class App extends Component<any, any> {
+      static template = xml`<div class="app">text</div>`;
+      static style = css`
+        .app {
+          color: red;
+        }
+      `;
+    }
+    class SubApp extends App {
+      static style = css`
+        .app {
+          font-weight: bold;
+        }
+      `;
+    }
+    expect(document.head.innerHTML).toBe("");
+    const app = new SubApp();
+
+    expect(document.head.innerHTML).toBe(`<style component=\"SubApp\">.app {
+  font-weight: bold;
+}</style><style component=\"App\">.app {
+  color: red;
+}</style>`);
+
+    await app.mount(fixture);
+    const style = getComputedStyle(app.el!);
+    expect(style.color).toBe("red");
+    expect(style.fontWeight).toBe("bold");
+    expect(fixture.innerHTML).toBe('<div class="app">text</div>');
+  });
+
+  test("get a meaningful error message if css helper is missing", async () => {
+    class App extends Component<any, any> {
+      static template = xml`<div class="app">text</div>`;
+      static style = `.app {color: red;}`;
+    }
+    let error;
+    try {
+      new App();
+    } catch (e) {
+      error = e;
+    }
+    expect(error).toBeDefined();
+    expect(error.message).toBe(
+      "Invalid css stylesheet for component 'App'. Did you forget to use the 'css' tag helper?"
+    );
+  });
+
+  test("inline stylesheets are processed", async () => {
+    class App extends Component<any, any> {
+      static template = xml`<div class="app">text</div>`;
+      static style = css`
+        .app {
+          color: red;
+          .some-class {
+            font-weight: bold;
+            width: 40px;
+          }
+
+          display: block;
+        }
+      `;
+    }
+    new App();
+
+    expect(document.head.querySelector("style")!.innerHTML).toBe(`.app {
+  color: red;
+}
+.app .some-class {
+  font-weight: bold;
+  width: 40px;
+}
+.app {
+  display: block;
+}`);
+  });
+});