Add expanded/collapsed state support for SwiftUI DisclosureGroup

[RoyalPineapple]

Summary

Adds support for reading the expanded/collapsed state from any accessibility element that exposes one — including UIKit elements that adopt iOS 18's accessibilityExpandedStatus and SwiftUI DisclosureGroup / expandable list sections. Accessibility snapshots now show whether these elements are expanded or collapsed, matching what VoiceOver announces to users.

What changed

• New ExpandedStatus enum on AccessibilityElement — unsupported, expanded, collapsed
• Reads _accessibilityExpandedStatus via the ObjC runtime on each accessibility element during parsing — works for both UIKit and SwiftUI sources
• Appends status to VoiceOver description — e.g. "Section. Button. Heading. Expanded."
• Appends hint — "Double tap to collapse." / "Double tap to expand.", appended to any existing hint
• Localized strings for en, de, ru
• Demo view + snapshot test for DisclosureGroup with reference images on iOS 17.5, 18.5, 26.2

Why read the private getter (and not the public iOS 18 API)

We chose _accessibilityExpandedStatus deliberately — it's the single source of truth that covers every element type that exposes expanded state, while the public accessibilityExpandedStatus only covers a subset:

Finding	Detail
Both APIs declared on NSObject	_accessibilityExpandedStatus (getter) and accessibilityExpandedStatus (getter/setter) are both declared directly on NSObject
Public setter syncs to private getter	On stock UIView/NSObject, setting the public property always updates the private getter — they share backing storage, so reading the private getter captures everything the public API captures
No private setter exists	_setAccessibilityExpandedStatus: does not exist on any class; the private key is also not KVC-compliant
SwiftUI overrides only the private getter	SwiftUI.AccessibilityNode overrides _accessibilityExpandedStatus to read from SwiftUI's internal accessibility graph, bypassing the shared storage entirely. The public getter returns 0 for all SwiftUI nodes — this appears to be a SwiftUI bug, with a standalone repro filed at RoyalPineapple/SwiftUIExpandedStatusBug
VoiceOver reads the private getter	When public and private values conflict, VoiceOver announces what _accessibilityExpandedStatus returns — confirmed on-device with iPhone 15
Rapid toggling never desyncs	On stock views, pub/priv stay perfectly in sync across all permutations

Conclusion: The private getter is the union of both worlds — it returns the correct value for UIKit elements (because the public setter syncs into it) and for SwiftUI elements (because SwiftUI overrides it). Reading the public API alone would miss every SwiftUI element. We use responds(to:) + method(for:) to read the value, consistent with how the codebase already reads other private accessibility properties.

Data flow

flowchart LR
    U["UIKit element\n(public API set)"] -->|"backing storage"| B
    S["SwiftUI AccessibilityNode\n(overrides private getter)"] -->|"override"| B
    B["_accessibilityExpandedStatus\n(read via NSObject extension)"]
    B -->|"ExpandedStatus enum"| C["AccessibilityElement\n.expandedStatus"]
    B -->|"rawStatus 1/2"| D["Description: 'Expanded.' / 'Collapsed.'"]
    B -->|"rawStatus 1/2"| E["Hint: 'Double tap to collapse/expand.'"]
    D --> F["Snapshot Legend"]
    E --> F

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Snapshot output

Before:

Section Header. Button. Heading.
  Hint: (none)

After:

Section Header. Button. Heading. Expanded.
  Hint: Double tap to collapse.

Related

• Apple bug repro for SwiftUI's missing public-API support: https://github.com/RoyalPineapple/SwiftUIExpandedStatusBug

Test plan

• SwiftUIDisclosureGroupTests snapshot test passes on iOS 17.5, 18.5, 26.2
• All existing snapshot tests unaffected
• Build succeeds after rebase onto main
• Runtime sync investigation: 12/12 tests pass confirming private API behavior on UIKit
• On-device VoiceOver verification with iPhone 15