Filter non-ItemView subviews out of accessibilityElements

CHANGELOG.md

@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed a performance issue caused by the item models for day ranges and month backgrounds not being cached
 - Fixed an issue that could cause the calendar to appear blank after rotating the device
 - Fixed an issue with touch handling on iOS 26
+- Fixed a crash when accessibility is enabled on iOS 27, caused by assuming that every subview of the calendar's scroll view is an item view
 
 ### Changed
 - Rewrote accessibility code to avoid posting notifications, which causes poor Voice Over performance and odd focus bugs

HorizonCalendar.xcodeproj/project.pbxproj

@@ -8,6 +8,7 @@
 
 /* Begin PBXBuildFile section */
 		086333B02AB8D36900CC6125 /* CalendarContentTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 086333AE2AB8D34700CC6125 /* CalendarContentTests.swift */; };
+		AB1200000000000000000002 /* CalendarScrollViewTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = AB1200000000000000000001 /* CalendarScrollViewTests.swift */; };
 		9321957E26EEB44C0001C7E9 /* DayOfWeekView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9321957D26EEB44C0001C7E9 /* DayOfWeekView.swift */; };
 		9321958026EEB6330001C7E9 /* Shape.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9321957F26EEB6330001C7E9 /* Shape.swift */; };
 		9321958226EEB6AB0001C7E9 /* DrawingConfig.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9321958126EEB6AB0001C7E9 /* DrawingConfig.swift */; };
@@ -88,6 +89,7 @@
 
 /* Begin PBXFileReference section */
 		086333AE2AB8D34700CC6125 /* CalendarContentTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CalendarContentTests.swift; sourceTree = "<group>"; };
+		AB1200000000000000000001 /* CalendarScrollViewTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CalendarScrollViewTests.swift; sourceTree = "<group>"; };
 		9321957D26EEB44C0001C7E9 /* DayOfWeekView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DayOfWeekView.swift; sourceTree = "<group>"; };
 		9321957F26EEB6330001C7E9 /* Shape.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Shape.swift; sourceTree = "<group>"; };
 		9321958126EEB6AB0001C7E9 /* DrawingConfig.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DrawingConfig.swift; sourceTree = "<group>"; };
@@ -243,6 +245,7 @@
 				939E694D2484B14400A8BCC7 /* VisibleItemsProviderTests.swift */,
 				9396F3D22483261B008AD306 /* Info.plist */,
 				086333AE2AB8D34700CC6125 /* CalendarContentTests.swift */,
+				AB1200000000000000000001 /* CalendarScrollViewTests.swift */,
 			);
 			path = Tests;
 			sourceTree = "<group>";
@@ -487,6 +490,7 @@
 				939E695C2484B22600A8BCC7 /* VisibleItemsProviderTests.swift in Sources */,
 				93A0062C24F206BE00F667A3 /* ItemViewReuseManagerTests.swift in Sources */,
 				086333B02AB8D36900CC6125 /* CalendarContentTests.swift in Sources */,
+				AB1200000000000000000002 /* CalendarScrollViewTests.swift in Sources */,
 				939E69592484B21700A8BCC7 /* LayoutItemTypeEnumeratorTests.swift in Sources */,
 				93FA64F2248D93EA00A8B7B1 /* MonthRowTests.swift in Sources */,
 				932E24142558DF6E001648D2 /* HorizontalMonthsLayoutOptionsTests.swift in Sources */,

Sources/Internal/CalendarScrollView.swift

@@ -51,9 +51,9 @@ final class CalendarScrollView: UIScrollView {
 
   override var accessibilityElements: [Any]? {
     get {
-      guard let itemViews = subviews as? [ItemView] else {
-        fatalError("Only `ItemView`s can be used as subviews of the scroll view.")
-      }
+      // UIKit can add subviews of its own - on iOS 27 it adds `_UITouchPassthroughView`s - so we
+      // filter to the item views rather than requiring that every subview is one.
+      let itemViews = subviews.compactMap { $0 as? ItemView }
       cachedAccessibilityElements = cachedAccessibilityElements ?? itemViews
         .filter {
           switch $0.itemType {

Tests/CalendarScrollViewTests.swift

@@ -0,0 +1,78 @@
+// Created by Andy Bartholomew on 8/12/26.
+// Copyright © 2026 Airbnb Inc. All rights reserved.
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import XCTest
+@testable import HorizonCalendar
+
+// MARK: - CalendarScrollViewTests
+
+final class CalendarScrollViewTests: XCTestCase {
+
+  // MARK: Internal
+
+  func testAccessibilityElementsIgnoresSubviewsThatAreNotItemViews() {
+    let scrollView = CalendarScrollView()
+    let itemView = itemView(for: .monthHeader(month))
+    scrollView.addSubview(itemView)
+
+    // UIKit adds subviews of its own on some OS versions - `_UITouchPassthroughView`s on iOS 27, for
+    // example - which must not prevent the item views from being returned.
+    scrollView.addSubview(UIView())
+
+    XCTAssertEqual(scrollView.accessibilityElements?.count, 1)
+    XCTAssert(scrollView.accessibilityElements?.first as? ItemView === itemView)
+  }
+
+  func testAccessibilityElementsWithNoItemViews() {
+    let scrollView = CalendarScrollView()
+    scrollView.addSubview(UIView())
+
+    XCTAssertEqual(scrollView.accessibilityElements?.count, 0)
+  }
+
+  // MARK: Private
+
+  private let month = Month(era: 1, year: 2026, month: 08, isInGregorianCalendar: true)
+
+  private func itemView(for itemType: LayoutItem.ItemType) -> ItemView {
+    let itemView = ItemView(initialCalendarItemModel: MockCalendarItemModel())
+    itemView.itemType = .layoutItemType(itemType)
+    return itemView
+  }
+
+}
+
+// MARK: - MockCalendarItemModel
+
+private struct MockCalendarItemModel: AnyCalendarItemModel {
+
+  var _itemViewDifferentiator = _CalendarItemViewDifferentiator(
+    viewType: ObjectIdentifier(UIView.self),
+    invariantViewProperties: AnyHashable(0)
+  )
+
+  func _makeView() -> UIView {
+    UIView()
+  }
+
+  func _setContent(onViewOfSameType _: UIView) { }
+
+  func _isContentEqual(toContentOf _: AnyCalendarItemModel) -> Bool {
+    false
+  }
+
+  mutating func _setSwiftUIWrapperViewContentIDIfNeeded(_: AnyHashable) { }
+
+}