Fixed crash of infinite scroll pager built with item_builder

commit_hash:0aa265991666f9e70459d1bfa1804f60c8698f08

client/ios/DivKit/Extensions/DivGallery/DivGalleryProtocol.swift

@@ -22,7 +22,7 @@ extension DivGalleryProtocol {
     scrollMode: GalleryViewModel.ScrollMode,
     columnCount: Int? = nil,
     infiniteScroll: Bool = false,
-    bufferSize: Int = 1,
+    layoutMode: PagerBlock.LayoutMode? = nil,
     scrollbar: GalleryViewModel.Scrollbar = .none,
     transformation: ElementsTransformation? = nil
   ) throws -> GalleryViewModel {
@@ -41,10 +41,10 @@ extension DivGalleryProtocol {
         )
       }
 
-    if let itemBuilder {
-      children = itemBuilder.makeBlocks(context: context, mappedBy: blockMapper)
+    children = if let itemBuilder {
+      itemBuilder.makeBlocks(context: context, mappedBy: blockMapper)
     } else {
-      children = nonNilItems.makeBlocks(
+      nonNilItems.makeBlocks(
         context: context,
         sizeModifier: DivGallerySizeModifier(
           context: context,
@@ -54,7 +54,10 @@ extension DivGalleryProtocol {
         mappedBy: blockMapper
       )
     }
-
+    
+    let itemsCount = children.count
+    let bufferSize = layoutMode.map { min($0.bufferSize(itemsCount: itemsCount), itemsCount) } ?? 1
+    
     if infiniteScroll {
       let leadingBuffer = children[..<bufferSize]
       let trailingBuffer = children[(children.count - bufferSize)...]
@@ -125,3 +128,16 @@ extension DivGalleryProtocol {
     return String(typeName)
   }
 }
+
+extension PagerBlock.LayoutMode {
+  fileprivate func bufferSize(itemsCount: Int) -> Int {
+    switch self {
+    case let .pageSize(relativeValue):
+      Int(1 / relativeValue.rawValue) + 1
+    case .neighbourPageSize:
+      2
+    case .pageContentSize:
+      itemsCount
+    }
+  }
+}

client/ios/DivKit/Extensions/DivPagerExtensions.swift

@@ -37,7 +37,7 @@ extension DivPager: DivBlockModeling, DivGalleryProtocol {
       defaultCrossAlignment: crossAlignment,
       scrollMode: .autoPaging(inertionEnabled: false),
       infiniteScroll: resolveInfiniteScroll(expressionResolver),
-      bufferSize: min(layoutMode.bufferSize(itemsCount: items.count), items.count),
+      layoutMode: layoutMode,
       transformation: pageTransformation?.resolve(
         expressionResolver,
         scrollDirection: scrollDirection
@@ -73,19 +73,6 @@ extension DivPager: DivBlockModeling, DivGalleryProtocol {
   }
 }
 
-extension PagerBlock.LayoutMode {
-  fileprivate func bufferSize(itemsCount: Int) -> Int {
-    switch self {
-    case let .pageSize(relativeValue):
-      Int(1 / relativeValue.rawValue) + 1
-    case .neighbourPageSize:
-      2
-    case .pageContentSize:
-      itemsCount
-    }
-  }
-}
-
 extension DivPager.Orientation {
   var direction: ScrollDirection {
     switch self {

client/ios/LayoutKit/LayoutKit/ViewModels/InfiniteScroll.swift

@@ -15,6 +15,11 @@ enum InfiniteScroll {
     alignment: Alignment = .center,
     insetMode: InsetMode = .fixed(values: .zero)
   ) -> Position? {
+    guard bufferSize > 0 else {
+      assertionFailure("Buffer size couldn't be less than one element for infinite scroll")
+      return nil
+    }
+
     let itemsCount = origins.count
     let cycleStartIndex = bufferSize
     let cycleEndIndex = itemsCount - bufferSize - 1