[FIX] components: ignore slot if no definition is given

closes #203

src/qweb_extensions.ts

@@ -705,11 +705,13 @@ QWeb.addDirective({
     ctx.addLine(
       `const slot${slotKey} = this.slots[context.__owl__.slotId + '_' + '${value}'];`
     );
+    ctx.addIf(`slot${slotKey}`)
     ctx.addLine(
       `slot${slotKey}(context.__owl__.parent, Object.assign({}, extra, {parentNode: c${
         ctx.parentNode
       }}));`
     );
+    ctx.closeIf();
     return true;
   }
 });

tests/__snapshots__/component.test.ts.snap

@@ -1083,12 +1083,16 @@ exports[`t-slot directive can define and call slots 2`] = `
     var vn2 = h('div', p2, c2);
     c1.push(vn2);
     const slot3 = this.slots[context.__owl__.slotId + '_' + 'header'];
-    slot3(context.__owl__.parent, Object.assign({}, extra, {parentNode: c2}));
+    if (slot3) {
+        slot3(context.__owl__.parent, Object.assign({}, extra, {parentNode: c2}));
+    }
     let c4 = [], p4 = {key:4};
     var vn4 = h('div', p4, c4);
     c1.push(vn4);
     const slot5 = this.slots[context.__owl__.slotId + '_' + 'footer'];
-    slot5(context.__owl__.parent, Object.assign({}, extra, {parentNode: c4}));
+    if (slot5) {
+        slot5(context.__owl__.parent, Object.assign({}, extra, {parentNode: c4}));
+    }
     return vn1;
 }"
 `;

tests/component.test.ts

@@ -3031,6 +3031,30 @@ describe("t-slot directive", () => {
     );
   });
 
+  test("missing slots are ignored", async () => {
+    env.qweb.addTemplates(`
+        <templates>
+          <div t-name="Parent">
+            <Dialog/>
+          </div>
+          <span t-name="Dialog">
+            <t t-slot="default"/>
+            <span>some content</span>
+            <t t-slot="footer"/>
+          </span>
+        </templates>
+    `);
+    class Dialog extends Widget {}
+    class Parent extends Widget {
+      components = { Dialog };
+    }
+    const parent = new Parent(env);
+    await parent.mount(fixture);
+
+    expect(fixture.innerHTML).toBe(
+      '<div><span><span>some content</span></span></div>'
+    );
+  });
 });
 
 describe("t-model directive", () => {