[IMP] template set config: getTemplate function

A template set can now obtain a template by calling the function
getTemplate (if any) received in the initial config.
The returned value can be an Element instance, a template string, a
function (i.e. a compiled template), or null. In the last case, owl will
look into the template set rawTemplates object.

tests/compiler/__snapshots__/template_set.test.ts.snap

@@ -101,3 +101,55 @@ exports[`loading templates can load a few templates from an XMLDocument 2`] = `
   }
 }"
 `;
+
+exports[`loading templates getTemplate: element returned (2) 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  let block1 = createBlock(\`<div>Hello World!</div>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;
+
+exports[`loading templates getTemplate: element returned 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  let block1 = createBlock(\`<div>Hello World!</div>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;
+
+exports[`loading templates getTemplate: template string returned 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  let block1 = createBlock(\`<div>Hello World!</div>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;
+
+exports[`loading templates getTemplate: undefined returned 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  let block1 = createBlock(\`<div>Hello World!</div>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;

tests/compiler/template_set.test.ts

@@ -78,4 +78,62 @@ describe("loading templates", () => {
     context.addTemplates(xml);
     expect(Object.keys(context.rawTemplates)).toEqual([]);
   });
+
+  test("getTemplate: element returned", () => {
+    const context = new TestContext({
+      getTemplate: (name) => {
+        if (name === "main") {
+          const data = `<div>Hello World!</div>`;
+          const xml = new DOMParser().parseFromString(data, "text/xml");
+          return xml.firstChild as Element;
+        }
+        return;
+      },
+    });
+    const result = context.renderToString("main");
+    expect(result).toBe("<div>Hello World!</div>");
+  });
+
+  test("getTemplate: element returned (2)", () => {
+    const context = new TestContext({
+      getTemplate: (name) => {
+        if (name === "main") {
+          const doc = new Document();
+          const div = doc.createElement("div");
+          div.append(doc.createTextNode("Hello World!"));
+          return div;
+        }
+        return;
+      },
+    });
+    const result = context.renderToString("main");
+    expect(result).toBe("<div>Hello World!</div>");
+  });
+
+  test("getTemplate: template string returned", () => {
+    const context = new TestContext({
+      getTemplate: (name) => {
+        if (name === "main") {
+          return `<div>Hello World!</div>`;
+        }
+        return;
+      },
+    });
+    const result = context.renderToString("main");
+    expect(result).toBe("<div>Hello World!</div>");
+  });
+
+  test("getTemplate: undefined returned", () => {
+    const context = new TestContext({
+      getTemplate: () => {},
+    });
+    const data = `<?xml version="1.0" encoding="UTF-8"?>
+    <templates id="template" xml:space="preserve">
+      <div t-name="main">Hello World!</div>
+    </templates>`;
+    const xml = new DOMParser().parseFromString(data, "text/xml");
+    context.addTemplates(xml);
+    const result = context.renderToString("main");
+    expect(result).toBe("<div>Hello World!</div>");
+  });
 });