[2.x] fix: tell assistive technology which dropdown option is selected

[imorland]

Fixes #3362.

A SelectDropdown shows which option is in effect two ways — a class on the item, and the toggle button borrowing that option's label. Neither reaches a screen reader, so moving through the menu announces an undifferentiated list of options with no indication of which one is active.

The selected item now carries aria-current="true".

Why aria-current and not aria-selected

The issue asks for aria-selected, but that attribute is only valid on elements with role option, tab, row, gridcell or treeitem. The menu is a plain <ul> of <li> wrapping buttons:

getMenu(items) {
  return <ul className={'Dropdown-menu dropdown-menu ' + this.attrs.menuClassName}>{items}</ul>;
}

with no role declared in Dropdown, SelectDropdown or Select. Adding aria-selected there would be ignored by assistive tech at best, and flagged as invalid by axe/Lighthouse at worst.

Giving the menu role="listbox" and its items role="option" would make it valid, but that is a contract — it commits us to arrow-key navigation and aria-activedescendant, which is a much bigger piece of work and belongs with #3361 and the rest of the keyboard-navigation issues. aria-current is valid on any element and states what is actually meant: the current item within a set.

Unselected items are left without the attribute rather than given "false". Only one item can be current, so the absence carries the meaning — and Mithril omits an attribute set to false regardless.

Scoping

The tidier place would have been listItems, which already works out which item is active and adds the active class. It is scoped to SelectDropdown instead because that helper wraps every list in Flarum, and the only component implementing isActive is LinkButton — which is route-based. Nav items are genuinely navigation and want aria-current="page", so marking them "true" would be wrong.

Tests

Three added to the existing SelectDropdown.test.ts:

• the selected option is marked — exactly one [aria-current="true"], and it is the right one
• unselected options are not marked — guards against applying it to everything
• nothing is marked when no option is selected — passes before this change as well as after; it is the guard against over-application

I checked the first two fail without the change rather than assuming it.

All integration suites green: 49 suites, 162 tests. check-typings clean.

To try it

Open a select dropdown — the sort dropdown on the discussion index is the clearest — and inspect the menu. The current option's <li> should carry aria-current="true" and the others should have no such attribute.