[IMP] runtime: add markup tag function

Allows markup to be called as a tag function. The interpolated strings
are then safely escaped for injection in HTML code.

Example usage:
```js
const maliciousInput = "<script>alert('💥💥')</script>";
const value = markup`<b>${maliciousInput}</b>`;
// no problem, maliciousInput is properly escaped
```

doc/reference/templates.md

@@ -193,6 +193,15 @@ The first `t-out` will act as a `t-esc` directive, which means that the content
 of `value1` will be escaped. However, since `value2` has been tagged as a markup,
 this will be injected as html.
 
+`markup` can also be used as a tag function, allowing the interpolated values to
+be safely escaped:
+
+```js
+const maliciousInput = "<script>alert('💥💥')</script>";
+// <b>&lt;script&gt;alert(&#x27;💥💥&#x27;)&lt;/script&gt;</b>
+const value = markup`<b>${maliciousInput}</b>`;
+```
+
 ### Setting Variables
 
 QWeb allows creating variables from within the template, to memoize a computation (to use it multiple times), give a piece of data a clearer name, ...

src/runtime/utils.ts

@@ -81,10 +81,50 @@ export async function loadFile(url: string): Promise<string> {
  */
 export class Markup extends String {}
 
+function _escapeHtml(str: any): string | Markup {
+  if (str instanceof Markup) {
+    return str;
+  }
+  if (str === undefined) {
+    return "";
+  }
+  if (typeof str === "number") {
+    return String(str);
+  }
+  [
+    ["&", "&amp;"],
+    ["<", "&lt;"],
+    [">", "&gt;"],
+    ["'", "&#x27;"],
+    ['"', "&quot;"],
+    ["`", "&#x60;"],
+  ].forEach((pairs) => {
+    str = String(str).replace(new RegExp(pairs[0], "g"), pairs[1]);
+  });
+  return str;
+}
+
 /*
  * Marks a value as safe, that is, a value that can be injected as HTML directly.
  * It should be used to wrap the value passed to a t-out directive to allow a raw rendering.
+ *
+ * If called as a tag function, the interpolated strings are escaped.
  */
-export function markup(value: any) {
+export function markup(strings: TemplateStringsArray, ...placeholders: unknown[]): Markup;
-  return new Markup(value);
+export function markup(value: string): Markup;
+export function markup(
+  valueOrStrings: string | TemplateStringsArray,
+  ...placeholders: unknown[]
+): Markup {
+  if (!Array.isArray(valueOrStrings)) {
+    return new Markup(valueOrStrings);
+  }
+  const strings = valueOrStrings;
+  let acc = "";
+  let i = 0;
+  for (; i < placeholders.length; ++i) {
+    acc += strings[i] + _escapeHtml(placeholders[i]);
+  }
+  acc += strings[i];
+  return new Markup(acc);
 }

tests/utils.test.ts

@@ -1,4 +1,4 @@
-import { batched, EventBus } from "../src/runtime/utils";
+import { batched, EventBus, markup } from "../src/runtime/utils";
 import { nextMicroTick } from "./helpers";
 
 describe("event bus behaviour", () => {
@@ -71,3 +71,33 @@ describe("batched", () => {
     expect(n).toBe(2);
   });
 });
+
+const Markup = markup("").constructor;
+describe("markup", () => {
+  test("string is flagged as safe", () => {
+    const html = markup("<blink>Hello</blink>");
+    expect(html).toBeInstanceOf(Markup);
+  });
+  describe("tag function", () => {
+    test("interpolated values are escaped", () => {
+      const maliciousInput = "<script>alert('💥💥')</script>";
+      const html = markup`<b>${maliciousInput}</b>`;
+      expect(html.toString()).toBe("<b>&lt;script&gt;alert(&#x27;💥💥&#x27;)&lt;/script&gt;</b>");
+      expect(html).toBeInstanceOf(Markup);
+    });
+    test("interpolated markups aren't escaped", () => {
+      const shouldBeEscaped = "<script>alert('should be escaped')</script>";
+      const shouldnt = markup("<b>this is safe</b>");
+      const html = markup`<div>${shouldBeEscaped} ${shouldnt}</div>`;
+      expect(html.toString()).toBe(
+        "<div>&lt;script&gt;alert(&#x27;should be escaped&#x27;)&lt;/script&gt; <b>this is safe</b></div>"
+      );
+      expect(html).toBeInstanceOf(Markup);
+    });
+    test("quotes in interpolated values are escaped", () => {
+      const imgUrl = `lol" onerror="alert('xss')`;
+      const html = markup`<img src="${imgUrl}">`;
+      expect(html.toString()).toBe(`<img src="lol&quot; onerror=&quot;alert(&#x27;xss&#x27;)">`);
+    });
+  });
+});