Show a default speaker where the platform lists none

- Safari enumerates no output devices at all, so the list arrived empty — and
  an empty array is truthy, so the Speaker heading rendered with nothing under
  it, which reads as a broken feature.
- Show one entry instead, named as the default, disabled, and marked as the
  selection: audio is going somewhere, and an unchecked lone row reads as
  nothing being chosen.
- D2 already says a row that cannot be chosen is shown disabled, never hidden.
- Covered by its condition rather than by the browser, so Linux CI checks it:
  one test that the view model hands over an empty list rather than none, one
  that the menu then draws the default.

src/components/CallFooterViewModel.test.ts

@@ -126,6 +126,46 @@ describe("createCallFooterViewModel", () => {
     });
   });
 
+  describe("audioOutputOptions", () => {
+    it("is an empty list, not absent, where the platform enumerates no outputs", () => {
+      platformMock.mockReturnValue("desktop");
+      outputSelectionMock.mockReturnValue(true);
+
+      const vm = createCallFooterViewModel(
+        testScope(),
+        buildMinimalCallViewModel(gridLayout),
+        mockMuteStates(),
+        mockMediaDevices({
+          audioInput: {
+            available$: constant(
+              new Map<string, DeviceLabel>([
+                ["mic1", { type: "name", name: "Microphone 1" }],
+              ]),
+            ),
+            selected$: constant(undefined),
+            select: vi.fn(),
+          },
+          // Safari enumerates no output devices whatsoever. Reproduced by the
+          // condition rather than by the browser, so it is checked on the
+          // Linux CI runners that have no Safari to check it with.
+          audioOutput: {
+            available$: constant(new Map<string, DeviceLabel>()),
+            selected$: constant(undefined),
+            select: vi.fn(),
+          },
+        }),
+        /* reactionIdentifier */ undefined,
+        { showControls: true, header: HeaderStyle.Standard },
+      );
+
+      // Empty rather than undefined: undefined means this menu has no notion
+      // of outputs at all, as the camera menu has none, and hides the section.
+      // Empty means there are none to list, and the menu still shows the
+      // section with a default in it, disabled.
+      expect(vm.audioOutputOptions$.value).toEqual([]);
+    });
+  });
+
   describe("audioOptions and videoOptions", () => {
     function checkEmptyFor(platform: string, layout: Layout): void {
       platformMock.mockReturnValue(platform);

src/components/MediaMuteAndSwitchButton.stories.tsx

@@ -197,3 +197,34 @@ export const OnlyOneDevice: Story = {
     await expect(only).toHaveAttribute("aria-disabled", "true");
   },
 };
+
+/**
+ * A platform that enumerates no output devices and offers no way to choose one
+ * — Safari. The section still names where audio is going, disabled, rather than
+ * leaving a heading with nothing under it.
+ */
+export const OutputNotEnumerated: Story = {
+  args: {
+    ...Default.args,
+    title: "Microphone",
+    iconsAndLabels: "audio",
+    enabled: true,
+    options: [
+      { label: { type: "name", name: "Microphone 1" }, id: "mic1" },
+      { label: { type: "name", name: "Microphone 2" }, id: "mic2" },
+    ],
+    selectedOption: "mic1",
+    outputOptions: [],
+    selectedOutputOption: undefined,
+    onSelectOutput: undefined,
+  },
+  play: async ({ canvasElement }) => {
+    const canvas = within(canvasElement);
+    await userEvent.click(canvas.getByRole("button", { name: "Microphone" }));
+
+    const speakers = await within(document.body).findByRole("menuitemradio", {
+      name: "Default",
+    });
+    await expect(speakers).toHaveAttribute("aria-disabled", "true");
+  },
+};

src/components/MediaMuteAndSwitchButton.test.tsx

@@ -7,7 +7,13 @@ Please see LICENSE in the repository root for full details.
 
 import { describe, expect, test, vi } from "vitest";
 import { axe } from "vitest-axe";
-import { act, render, screen, type RenderResult } from "@testing-library/react";
+import {
+  act,
+  render,
+  screen,
+  within,
+  type RenderResult,
+} from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { type JSX, useState, type ReactNode } from "react";
 import { TooltipProvider } from "@vector-im/compound-web";
@@ -613,6 +619,46 @@ describe("MediaMuteAndSwitchButton", () => {
     expect(only).toHaveAttribute("aria-disabled", "true");
   });
 
+  test("shows a default speaker where the platform lists none", async () => {
+    const user = userEvent.setup();
+    const { getByRole } = renderComponent(
+      <MediaMuteAndSwitchButton
+        title="Switcher"
+        iconsAndLabels="audio"
+        enabled={true}
+        options={[
+          { label: { type: "name", name: "Microphone 1" }, id: "mic1" },
+          { label: { type: "name", name: "Microphone 2" }, id: "mic2" },
+        ]}
+        selectedOption="mic1"
+        onSelect={vi.fn()}
+        // Safari enumerates no output devices at all, and offers no way to
+        // choose one.
+        outputOptions={[]}
+        selectedOutputOption={undefined}
+        onSelectOutput={undefined}
+      />,
+    );
+
+    await user.click(getByRole("button", { name: "Microphone" }));
+
+    // A heading with nothing under it says the feature is broken. Audio is
+    // playing somewhere, so the section names that somewhere and disables it.
+    const speakers = screen
+      .getAllByRole("group")
+      .find((group) => group.getAttribute("aria-label") === "Speaker")!;
+    const entries = within(speakers).getAllByRole("menuitemradio");
+    expect(entries).toHaveLength(1);
+    expect(entries[0]).toHaveAccessibleName("Default");
+    expect(entries[0]).toHaveAttribute("aria-disabled", "true");
+    // And marked as the selection: it is where audio is going, so an unchecked
+    // lone entry would read as nothing being chosen at all.
+    expect(entries[0]).toHaveAttribute("aria-checked", "true");
+    expect(
+      within(entries[0]).getByRole("radio", { hidden: true }),
+    ).toBeChecked();
+  });
+
   test("shows the speaker section disabled when output selection is unsupported", async () => {
     const user = userEvent.setup();
     const { getByRole } = renderComponent(

src/components/MediaMuteAndSwitchButton.tsx

@@ -85,6 +85,14 @@ export interface MediaMuteAndSwitchButtonProps {
 
 const BLUR_ID = "blur";
 
+/**
+ * Stands for wherever the platform is sending audio, where it will not say.
+ *
+ * Not a device id the browser would recognise: nothing can be selected on a
+ * platform that lists no outputs, so this is only ever shown, never sent.
+ */
+const DEFAULT_OUTPUT_ID = "default";
+
 export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
   title,
   enabled,
@@ -251,6 +259,21 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
         ? selectedOutputOption
         : selectedOption);
 
+  // Safari enumerates no output devices at all, and offers no way to choose
+  // one, so the list arrives empty. The section is shown all the same — audio
+  // is playing somewhere — naming that somewhere and disabling it like any
+  // single entry. A heading with nothing beneath it reads as a broken feature,
+  // and leaves the menu a different shape on one browser.
+  const noOutputsListed = outputOptions?.length === 0;
+  const speakerOptions: MenuOptions[] | undefined = noOutputsListed
+    ? [{ id: DEFAULT_OUTPUT_ID, label: { type: "default", name: null } }]
+    : outputOptions;
+  // And it is the selection, not merely the only row: it is where audio is
+  // going. An unchecked lone entry reads as nothing being chosen at all.
+  const selectedSpeaker = noOutputsListed
+    ? DEFAULT_OUTPUT_ID
+    : selectedOutputOption;
+
   const deviceItems = (
     kind: "input" | "output",
     items: MenuOptions[] | undefined,
@@ -356,7 +379,7 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
             } as CSSProperties
           }
         >
-          {iconsAndLabels === "audio" && outputOptions && (
+          {iconsAndLabels === "audio" && speakerOptions && (
             <>
               {/* A menu may only contain items, separators and groups, so each
                   heading belongs to a group rather than sitting beside the
@@ -369,8 +392,8 @@ export const MediaMuteAndSwitchButton: FC<MediaMuteAndSwitchButtonProps> = ({
                 </div>
                 {deviceItems(
                   "output",
-                  outputOptions,
+                  speakerOptions,
-                  selectedOutputOption,
+                  selectedSpeaker,
                   onSelectOutput,
                   (n) => t("settings.devices.speaker_numbered", { n }),
                 )}