add bridge between layout provider and adapter

SectionKit/Sources/CollectionViewAdapter/ListCollectionViewAdapter/ListCollectionViewAdapter+Convenience.swift

@@ -58,12 +58,12 @@ extension ListCollectionViewAdapter {
 extension ListCollectionViewAdapter {
     @inlinable
     public func flowDelegate(at indexPath: IndexPath) -> SectionFlowDelegate? {
-        controller(at: indexPath)?.flowDelegate
+        (controller(at: indexPath) as? FlowLayoutSectionController)?.flowDelegate
     }
 
     @inlinable
     public func flowDelegate(at index: Int) -> SectionFlowDelegate? {
-        controller(at: index)?.flowDelegate
+        (controller(at: index) as? FlowLayoutSectionController)?.flowDelegate
     }
 }
 

SectionKit/Sources/CollectionViewAdapter/ListCollectionViewAdapter/ListCollectionViewAdapter.swift

@@ -49,6 +49,12 @@ open class ListCollectionViewAdapter: NSObject, CollectionViewAdapter {
             collectionView.dragDelegate = self
             collectionView.dropDelegate = self
         }
+        if #available(iOS 13.0, *),
+           let layout = collectionView.collectionViewLayout as? SectionKitCompositionalLayout {
+            layout.sections = { [weak self] in
+                self?.collectionViewSections ?? []
+            }
+        }
     }
 
     /**
@@ -90,6 +96,12 @@ open class ListCollectionViewAdapter: NSObject, CollectionViewAdapter {
             collectionView.dragDelegate = self
             collectionView.dropDelegate = self
         }
+        if #available(iOS 13.0, *),
+           let layout = collectionView.collectionViewLayout as? SectionKitCompositionalLayout {
+            layout.sections = { [weak self] in
+                self?.collectionViewSections ?? []
+            }
+        }
     }
 
     public let context: CollectionViewContext

SectionKit/Sources/CollectionViewAdapter/SingleSectionCollectionViewAdapter/SingleSectionCollectionViewAdapter+Convenience.swift

@@ -58,12 +58,12 @@ extension SingleSectionCollectionViewAdapter {
 extension SingleSectionCollectionViewAdapter {
     @inlinable
     public func flowDelegate(at indexPath: IndexPath) -> SectionFlowDelegate? {
-        controller(at: indexPath)?.flowDelegate
+        (controller(at: indexPath) as? FlowLayoutSectionController)?.flowDelegate
     }
 
     @inlinable
     public func flowDelegate(at index: Int) -> SectionFlowDelegate? {
-        controller(at: index)?.flowDelegate
+        (controller(at: index) as? FlowLayoutSectionController)?.flowDelegate
     }
 }
 

SectionKit/Sources/Utility/CompositionalLayout/NSCollectionLayoutSection+Empty.swift

@@ -0,0 +1,18 @@
+import UIKit
+
+@available(iOS 13.0, *)
+extension NSCollectionLayoutSection {
+    static let empty: NSCollectionLayoutSection = {
+        let layoutSize = NSCollectionLayoutSize(
+            widthDimension: .absolute(0),
+            heightDimension: .absolute(0)
+        )
+        return NSCollectionLayoutSection(
+            group: .vertical(
+                layoutSize: layoutSize,
+                subitem: .init(layoutSize: layoutSize),
+                count: 1
+            )
+        )
+    }()
+}

SectionKit/Sources/Utility/CompositionalLayout/SectionKitCompositionalLayout.swift

@@ -0,0 +1,53 @@
+import UIKit
+
+/// This compositional layout is designed for the section kit.
+/// It ensures that the layout provider utilizes the layout section provided by the compositional layout section controller.
+@MainActor
+@available(iOS 13.0, *)
+final public class SectionKitCompositionalLayout: UICollectionViewCompositionalLayout {
+    // Use internally to bridge the sections from the adapter to the section provider.
+    var sections: (() -> [Section])?
+
+    public init() {
+        var sections: (() -> [Section])?
+        super.init { index, environment in
+            guard let sections = sections?() else {
+                assertionFailure("The section provider doesn't set up correctly, please use the `CollectionViewCompositionalLayoutAdapter`")
+                return .empty
+            }
+            guard sections.count > index else {
+                assertionFailure("Section index out of bound")
+                return .empty
+            }
+            guard let compositionalLayoutSectionController = sections[index].controller
+                    as? BaseCompositionalLayoutSectionController else {
+                assertionFailure("Please use the `CompositionalLayoutSectionControler`")
+                return .empty
+            }
+            return compositionalLayoutSectionController.layoutSection(
+                layoutEnvironment: environment
+            )
+        }
+        sections = { [weak self] in
+            self?.sections?() ?? []
+        }
+    }
+
+    @available(*, unavailable)
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    @available(*, unavailable)
+    override init(
+        sectionProvider: @escaping UICollectionViewCompositionalLayoutSectionProvider,
+        configuration: UICollectionViewCompositionalLayoutConfiguration
+    ) {
+        fatalError("init(sectionProvider:configuration:) has not been implemented")
+    }
+
+    @available(*, unavailable)
+    override init(sectionProvider: @escaping UICollectionViewCompositionalLayoutSectionProvider) {
+        fatalError("init(sectionProvider:) has not been implemented")
+    }
+}