[IMP] components: slots can now define default content

closes #554

doc/reference/component.md

@@ -865,6 +865,19 @@ be considered the `default` slot. For example:
 </div>
 ```
 
+Slots can define a default content, in case the parent did not define them:
+
+```xml
+<div t-name="Parent">
+  <Child/>
+</div>
+
+<span t-name="Child">
+  <t t-slot="default">default content</t>
+</span>
+<!-- will be rendered as: <div><span>default content</span></div> -->
+```
+
 ### Dynamic sub components
 
 It is not common, but sometimes we need a dynamic component name. In this case,

src/qweb/extensions.ts

@@ -194,7 +194,7 @@ QWeb.addDirective({
 QWeb.addDirective({
   name: "slot",
   priority: 80,
-  atNodeEncounter({ ctx, value }): boolean {
+  atNodeEncounter({ ctx, value, node, qweb }): boolean {
     const slotKey = ctx.generateID();
     ctx.addLine(
       `const slot${slotKey} = this.constructor.slots[context.__owl__.slotId + '_' + '${value}'];`
@@ -214,6 +214,12 @@ QWeb.addDirective({
     if (!ctx.parentNode) {
       ctx.addLine(`utils.defineProxy(result, ${parentNode}[0]);`);
     }
+    if (node.hasChildNodes()) {
+      ctx.addElse();
+      const nodeCopy = <Element>node.cloneNode(true);
+      nodeCopy.removeAttribute("t-slot");
+      qweb._compileNode(nodeCopy, ctx);
+    }
     ctx.closeIf();
     return true;
   }

tests/component/__snapshots__/component.test.ts.snap

@@ -1395,6 +1395,23 @@ exports[`t-slot directive content is the default slot 1`] = `
 }"
 `;
 
+exports[`t-slot directive dafault slots can define a default content 1`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"__template__1\\"
+    var h = this.h;
+    let c5 = [], p5 = {key:5};
+    var vn5 = h('span', p5, c5);
+    const slot6 = this.constructor.slots[context.__owl__.slotId + '_' + 'default'];
+    if (slot6) {
+        slot6.call(this, context.__owl__.scope, Object.assign({}, extra, {parentNode: c5, parent: extra.parent || context}));
+    } else {
+        c5.push({text: \`default content\`});
+    }
+    return vn5;
+}"
+`;
+
 exports[`t-slot directive default slot work with text nodes 1`] = `
 "function anonymous(context, extra
 ) {
@@ -1439,6 +1456,23 @@ exports[`t-slot directive multiple roots are allowed in a named slot 1`] = `
 }"
 `;
 
+exports[`t-slot directive named slots can define a default content 1`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"__template__1\\"
+    var h = this.h;
+    let c5 = [], p5 = {key:5};
+    var vn5 = h('span', p5, c5);
+    const slot6 = this.constructor.slots[context.__owl__.slotId + '_' + 'header'];
+    if (slot6) {
+        slot6.call(this, context.__owl__.scope, Object.assign({}, extra, {parentNode: c5, parent: extra.parent || context}));
+    } else {
+        c5.push({text: \`default content\`});
+    }
+    return vn5;
+}"
+`;
+
 exports[`t-slot directive refs are properly bound in slots 1`] = `
 "function anonymous(context, extra
 ) {

tests/component/component.test.ts

@@ -4032,6 +4032,76 @@ describe("t-slot directive", () => {
     expect(QWeb.slots["1_footer"].toString()).toMatchSnapshot();
   });
 
+  test("named slots can define a default content", async () => {
+    class Dialog extends Component<any, any> {
+      static template = xml`
+        <span>
+          <t t-slot="header">default content</t>
+        </span>`;
+    }
+    class Parent extends Component<any, any> {
+      static template = xml`<div><Dialog/></div>`;
+      static components = { Dialog };
+    }
+    const parent = new Parent();
+    await parent.mount(fixture);
+
+    expect(fixture.innerHTML).toBe("<div><span>default content</span></div>");
+    expect(env.qweb.templates[Dialog.template].fn.toString()).toMatchSnapshot();
+  });
+
+  test("dafault slots can define a default content", async () => {
+    class Dialog extends Component<any, any> {
+      static template = xml`
+        <span>
+          <t t-slot="default">default content</t>
+        </span>`;
+    }
+    class Parent extends Component<any, any> {
+      static template = xml`<div><Dialog/></div>`;
+      static components = { Dialog };
+    }
+    const parent = new Parent();
+    await parent.mount(fixture);
+
+    expect(fixture.innerHTML).toBe("<div><span>default content</span></div>");
+    expect(env.qweb.templates[Dialog.template].fn.toString()).toMatchSnapshot();
+  });
+
+  test("default content is not rendered if slot is provided", async () => {
+    class Dialog extends Component<any, any> {
+      static template = xml`
+        <span>
+          <t t-slot="default">default content</t>
+        </span>`;
+    }
+    class Parent extends Component<any, any> {
+      static template = xml`<div><Dialog>hey</Dialog></div>`;
+      static components = { Dialog };
+    }
+    const parent = new Parent();
+    await parent.mount(fixture);
+
+    expect(fixture.innerHTML).toBe("<div><span>hey</span></div>");
+  });
+
+  test("default content is not rendered if named slot is provided", async () => {
+    class Dialog extends Component<any, any> {
+      static template = xml`
+        <span>
+          <t t-slot="header">default content</t>
+        </span>`;
+    }
+    class Parent extends Component<any, any> {
+      static template = xml`<div><Dialog><t t-set="header">hey</t></Dialog></div>`;
+      static components = { Dialog };
+    }
+    const parent = new Parent();
+    await parent.mount(fixture);
+
+    expect(fixture.innerHTML).toBe("<div><span>hey</span></div>");
+  });
+
   test("slots are rendered with proper context", async () => {
     env.qweb.addTemplates(`
         <templates>