[FIX] web: renderToElement should always returns an element

Before this commit, when the first element of a template is a non
fulfilled condition :
'<t t-if="false"/>'
The function renderToElement returns an empty text. This occurs because
it returns the first child, which in this case is an empty text.

Now, the function returns the first element.

closes odoo/odoo#130858

X-original-commit: 8dabc4e1d5ebd94f6a315ce56b9bf60240dd7fdd
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>
Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>

addons/web/static/src/core/utils/render.js

@@ -3,7 +3,7 @@
 import { blockDom, markup } from "@odoo/owl";
 
 export function renderToElement(template, context = {}) {
-    return render(template, context).firstChild;
+    return render(template, context).firstElementChild;
 }
 
 /**

addons/web/static/tests/core/utils/render_tests.js

@@ -0,0 +1,26 @@
+/** @odoo-module **/
+
+import { renderToElement, renderToString } from "@web/core/utils/render";
+
+QUnit.module("utils", () => {
+    QUnit.module("render");
+
+    QUnit.test("renderToElement always returns an element", (assert) => {
+        renderToString.app.addTemplate(
+            "test.render.template.1",
+            `<t t-if="False">
+              <div>NotOk</div>
+            </t>
+            <t t-else="">
+              <div>Ok</div>
+            </t>`
+        );
+        const compiledTemplate = renderToElement("test.render.template.1");
+        assert.strictEqual(
+            compiledTemplate.nodeType,
+            Node.ELEMENT_NODE,
+            "compiledTemplate must be an element"
+        );
+        assert.strictEqual(compiledTemplate.outerHTML, "<div>Ok</div>");
+    });
+});