a11y: localize aria-label on form-control elements (<select>, <input>, <textarea>) (#7713)

#7584 introduced auto-population of aria-label from a translation
when an element has data-l10n-id and no author-supplied aria-label.
That branch only fires for elements with no children (or with
data-l10n-id ending in a recognized attribute suffix like .title).

Form-control elements break the assumption: a <select> always has
<option> children, an <input>/<textarea> may have implicit value
content. The textContent branch handles them, but the aria-label
fallback wasn't called from there. Plugins like ep_font_size,
ep_headings2, and ep_hljs end up with a localized translation
applied to a <select> but no accessible name on the element itself.

Calls populateAriaLabel() from the textContent branch when the node
is a <select>, <input>, or <textarea>. Keeps the same
"author-supplied aria-label wins on first pass; the
data-l10n-aria-label marker lets us refresh values we wrote"
semantics from #7584.

Adds Playwright coverage in
src/tests/frontend-new/specs/html10n_form_controls_aria.spec.ts:
- aria-label is populated on <select> with data-l10n-id
- aria-label is populated on <textarea> with data-l10n-id
- author-supplied aria-label is preserved on first pass

src/static/js/vendors/html10n.ts

@@ -658,24 +658,28 @@ export class Html10n {
       prop = document.body.textContent ? 'textContent' : 'innerText'
     }
 
-    // Apply translation
-    if (node.children.length === 0 || prop != 'textContent') {
-      // @ts-ignore
-      node[prop] = str.str!
-      // Populate aria-label from the translation so screen readers get a
-      // localized accessible name. Preserve an author-supplied aria-label
-      // (one present in the template without a marker), but keep our own
-      // html10n-generated values in sync across language changes by
-      // overwriting them. The `data-l10n-aria-label` marker distinguishes
-      // the two: set when we populate it, checked on subsequent passes so
-      // `pad.applyLanguage()` refreshes the accessible name.
-      // See PR #7584 review feedback.
-      const generatedMarker = 'data-l10n-aria-label';
+    // Populate aria-label from the translation so screen readers get a
+    // localized accessible name. Preserve an author-supplied aria-label
+    // (one present in the template without a marker), but keep our own
+    // html10n-generated values in sync across language changes by
+    // overwriting them. The `data-l10n-aria-label` marker distinguishes
+    // the two: set when we populate it, checked on subsequent passes so
+    // `pad.applyLanguage()` refreshes the accessible name.
+    // See PR #7584 review feedback.
+    const generatedMarker = 'data-l10n-aria-label';
+    const populateAriaLabel = () => {
       if (!node.hasAttribute('aria-label') ||
           node.getAttribute(generatedMarker) === 'true') {
         node.setAttribute('aria-label', str.str!);
         node.setAttribute(generatedMarker, 'true');
       }
+    }
+
+    // Apply translation
+    if (node.children.length === 0 || prop != 'textContent') {
+      // @ts-ignore
+      node[prop] = str.str!
+      populateAriaLabel()
     } else {
       let children = node.childNodes,
         found = false
@@ -693,6 +697,17 @@ export class Html10n {
       if (!found) {
         console.warn('Unexpected error: could not translate element content for key '+str.id, node)
       }
+      // Form-controllable elements (<select>, <input>, <textarea>) carry their
+      // accessible name on aria-label rather than as text content (a <select>'s
+      // text is its <option> labels, not its own name). The textContent branch
+      // above doesn't fall through to populateAriaLabel(), so plugins that put
+      // data-l10n-id on a <select> and rely on the auto-population (introduced
+      // in #7584) end up with no accessible name. Populate aria-label here so
+      // those controls stay localized too. See ether/ep_align#182 review.
+      const tag = node.tagName;
+      if (tag === 'SELECT' || tag === 'INPUT' || tag === 'TEXTAREA') {
+        populateAriaLabel()
+      }
     }
   }
 

src/tests/frontend-new/specs/html10n_form_controls_aria.spec.ts

@@ -0,0 +1,85 @@
+// Regression test for html10n's aria-label auto-population on form
+// controls (<select>, <input>, <textarea>) — these have child <option>s
+// or implicit value content, so the textContent branch in translateNode
+// applies, and the aria-label population that lives in the no-children
+// branch was being skipped. This left plugins like ep_font_size and
+// ep_headings2 with a <select data-l10n-id="..."> but no accessible
+// name once a hardcoded English aria-label was removed.
+//
+// See ether/etherpad PR that added this behavior (linked from
+// ether/ep_align#182 review).
+
+import {expect, test} from '@playwright/test';
+import {goToNewPad} from '../helper/padHelper';
+
+test.use({locale: 'en-US'});
+
+test.beforeEach(async ({page}) => {
+  await goToNewPad(page);
+});
+
+test('html10n auto-populates aria-label on <select> with data-l10n-id', async ({page}) => {
+  // Inject a <select> with options into the toolbar, tagged with an
+  // existing translation key (`pad.toolbar.bold.title` is shipped in
+  // every locale).
+  await page.evaluate(() => {
+    const sel = document.createElement('select');
+    sel.id = 'html10n-test-select';
+    sel.setAttribute('data-l10n-id', 'pad.toolbar.bold.title');
+    const opt = document.createElement('option');
+    opt.value = 'a';
+    opt.textContent = 'A';
+    sel.appendChild(opt);
+    document.body.appendChild(sel);
+    // Trigger a re-translate so html10n sees the new node.
+    // @ts-ignore window.html10n is exposed by pad.ts
+    window.html10n.localize(['en']);
+  });
+
+  const sel = page.locator('#html10n-test-select');
+  // After translation, aria-label should be set from the localized
+  // string, and the data-l10n-aria-label marker should signal that
+  // html10n owns it (so applyLanguage refreshes it on language change).
+  await expect(sel).toHaveAttribute('aria-label', /.+/);
+  await expect(sel).toHaveAttribute('data-l10n-aria-label', 'true');
+});
+
+test('html10n auto-populates aria-label on <textarea> with data-l10n-id', async ({page}) => {
+  await page.evaluate(() => {
+    const ta = document.createElement('textarea');
+    ta.id = 'html10n-test-textarea';
+    ta.setAttribute('data-l10n-id', 'pad.toolbar.bold.title');
+    document.body.appendChild(ta);
+    // @ts-ignore
+    window.html10n.localize(['en']);
+  });
+
+  const ta = page.locator('#html10n-test-textarea');
+  await expect(ta).toHaveAttribute('aria-label', /.+/);
+  await expect(ta).toHaveAttribute('data-l10n-aria-label', 'true');
+});
+
+test('an author-supplied aria-label on a form control is preserved', async ({page}) => {
+  // Mirror the existing semantics for non-form-control elements: if the
+  // template author wrote their own aria-label, html10n must not
+  // overwrite it on the first pass (it can only refresh values it
+  // previously wrote, identified by the data-l10n-aria-label marker).
+  await page.evaluate(() => {
+    const sel = document.createElement('select');
+    sel.id = 'html10n-test-author-aria';
+    sel.setAttribute('data-l10n-id', 'pad.toolbar.bold.title');
+    sel.setAttribute('aria-label', 'Custom author label');
+    const opt = document.createElement('option');
+    opt.value = 'a';
+    opt.textContent = 'A';
+    sel.appendChild(opt);
+    document.body.appendChild(sel);
+    // @ts-ignore
+    window.html10n.localize(['en']);
+  });
+
+  const sel = page.locator('#html10n-test-author-aria');
+  await expect(sel).toHaveAttribute('aria-label', 'Custom author label');
+  // No marker is set — html10n didn't write this one.
+  await expect(sel).not.toHaveAttribute('data-l10n-aria-label', 'true');
+});