implemented a11y for galleries

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/GalleryGridView.swift

@@ -72,6 +72,7 @@ struct GalleryGridView: View {
             let overflow = (overflowCount > 0 && isLastVisible) ? overflowCount : 0
             
             GalleryItemTileView(item: items[index],
+                                position: index + 1,
                                 mediaProvider: mediaProvider,
                                 contentScannerService: contentScannerService,
                                 overflowCount: overflow) {

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/GalleryItemTileView.swift

@@ -10,11 +10,25 @@ import SwiftUI
 
 struct GalleryItemTileView: View {
     let item: GalleryItem
+    /// The item's position within the gallery, announced instead of its filename.
+    let position: Int
     let mediaProvider: MediaProviderProtocol?
     let contentScannerService: ContentScannerServiceProtocol?
     let overflowCount: Int
     let onTap: () -> Void
     
+    private var accessibilityLabel: String {
+        if overflowCount > 0 {
+            L10n.a11yGalleryMoreMedia(overflowCount)
+        } else if item.isVideo {
+            L10n.a11yGalleryVideo(position)
+        } else if item.isImage {
+            L10n.a11yGalleryImage(position)
+        } else {
+            L10n.a11yGalleryAttachment(position)
+        }
+    }
+    
     var body: some View {
         // Overflow above the scanner: shows on any scan state, survives content updates.
         ZStack {
@@ -33,11 +47,15 @@ struct GalleryItemTileView: View {
                         }
                     }
                     .accessibilityElement(children: .ignore)
-                    .accessibilityLabel(item.filename)
+                    .accessibilityLabel(accessibilityLabel)
             } scanningContent: {
                 ScanningMediaEventsTimelineView()
+                    .accessibilityElement(children: .ignore)
+                    .accessibilityLabel(L10n.a11yGalleryScanning(position))
             } unsafeContent: { failure in
                 UnsafeMediaEventsTimelineView(failure: failure)
+                    .accessibilityElement(children: .ignore)
+                    .accessibilityLabel(L10n.a11yGalleryFailedScan(position))
             }
             
             if overflowCount > 0 {
@@ -47,6 +65,9 @@ struct GalleryItemTileView: View {
         // Tappable in every scan state, so that an unsafe item can't hide the rest of the gallery.
         .contentShape(Rectangle())
         .onTapGesture { onTap() }
+        // One element per tile, labelled by whichever state is on show.
+        .accessibilityElement(children: .combine)
+        .accessibilityAddTraits(.isButton)
     }
     
     @ViewBuilder
@@ -109,6 +130,7 @@ struct GalleryItemTileView: View {
                 .foregroundStyle(.compound.textPrimary)
         }
         .allowsHitTesting(false) // Let the tap fall through to the tile below.
+        .accessibilityHidden(true) // The count is already announced by the tile's label.
     }
     
     private func formatted(duration: TimeInterval) -> String {

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/GalleryListView.swift

@@ -24,6 +24,7 @@ struct GalleryListView: View {
                 }
                 
                 GalleryListRow(item: item,
+                               position: index + 1,
                                mediaProvider: mediaProvider,
                                contentScannerService: contentScannerService) {
                     onItemTap(index)
@@ -46,6 +47,8 @@ struct GalleryDivider: View {
 
 private struct GalleryListRow: View {
     let item: GalleryItem
+    /// The item's position within the gallery, prepended to the row's own description.
+    let position: Int
     let mediaProvider: MediaProviderProtocol?
     let contentScannerService: ContentScannerServiceProtocol?
     let onTap: () -> Void
@@ -71,6 +74,13 @@ private struct GalleryListRow: View {
         } unsafeContent: { failure in
             failureRow(failure)
         }
+        // One element per row, so that each attachment is focussed on its own, with its position
+        // prepended to the description that the row already provides.
+        .accessibilityElement(children: .combine)
+        .accessibilityLabel { label in
+            Text(L10n.a11yGalleryAttachment(position))
+            label
+        }
     }
     
     private func row(icon: some View) -> some View {

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/GalleryRoomTimelineView.swift

@@ -41,6 +41,7 @@ struct GalleryRoomTimelineView: View {
                         GalleryDivider()
                     }
                     caption
+                        .accessibilityHidden(true) // Announced when entering the gallery, so not a stop of its own.
                 }
             }
             .frame(width: GalleryGridView.groupWidth, alignment: .leading)