Isolate the UIKit-facing API to the main actor

Package.swift

@@ -4,7 +4,7 @@ import PackageDescription
 
 let package = Package(
     name: "CellKit",
-    platforms: [.iOS(.v9), .tvOS(.v9)],
+    platforms: [.iOS(.v13), .tvOS(.v13)],
     products: [
         .library(
             name: "CellKit",

Sources/CellKit/CellConfigurable.swift

@@ -1,3 +1,4 @@
+@MainActor
 public protocol CellConfigurable: AnyObject {
     associatedtype Model
     func configure(with model: Model)

Sources/CellKit/CellConvertible.swift

@@ -2,6 +2,7 @@
 //  CellConvertible.swift
 public typealias ReusableCellConvertible = CellConvertible & ReusableView
 
+@MainActor
 public protocol CellConvertible {
     associatedtype Cell: CellConfigurable
 }

Sources/CellKit/CellModel.swift

@@ -1,3 +1,4 @@
+@MainActor
 public protocol CellModel: ReusableView {
     var cellHeight: Double { get }
     var highlighting: Bool { get }
@@ -20,6 +21,7 @@ public extension CellModel {
     }
 }
 
+@MainActor
 public protocol SupplementaryViewModel: ReusableView {
     var height: Double { get }
 

Sources/CellKit/CellModelDataSource.swift

@@ -1,9 +1,11 @@
 import struct Foundation.IndexPath
 
+@MainActor
 public protocol CellModelDataSourceDelegate: AnyObject {
     func didSelectCellModel(_ cellModel: CellModel, at indexPath: IndexPath)
 }
 
+@MainActor
 open class CellModelDataSource: AbstractDataSource, DataSource {
 
     public var sections: [CellModelSection]

Sources/CellKit/CellModelSelectable.swift

@@ -1,3 +1,4 @@
+@MainActor
 public protocol CellModelSelectable {
     func didSelect()
 }

Sources/CellKit/DataSource.swift

@@ -1,5 +1,6 @@
 import UIKit
 
+@MainActor
 public protocol DataSource {
     associatedtype Section
 
@@ -9,6 +10,7 @@ public protocol DataSource {
     subscript(index: Int) -> Section { get }
 }
 
+@MainActor
 open class AbstractDataSource: NSObject {
 
     public weak var delegate: CellModelDataSourceDelegate?

Sources/CellKit/DiffableDataSources/CollectionSupplementaryViewModel.swift

@@ -1,4 +1,5 @@
 @available(iOS 13.0, tvOS 13.0, *)
+@MainActor
 public protocol CollectionSupplementaryViewModel: ReusableView {
     var kind: SupplementaryElementKind { get }
 

Sources/CellKit/DiffableDataSources/LazyCellProvider.swift

@@ -1,6 +1,7 @@
 import UIKit
 
 @available(iOS 13.0, tvOS 13.0, *)
+@MainActor
 public final class LazyCellProvider {
     private var registeredIdentifiers: Set<String>
 

Sources/CellKit/DiffableDataSources/LazySupplementaryViewProvider.swift

@@ -1,6 +1,7 @@
 import UIKit
 
 @available(iOS 13.0, tvOS 13.0, *)
+@MainActor
 public final class LazySupplementaryViewProvider {
 
     private var registeredIdentifiers: [String: Set<String>]

Sources/CellKit/ReusableView.swift

@@ -1,6 +1,7 @@
 import class Foundation.Bundle
 import class UIKit.UINib
 
+@MainActor
 public protocol ReusableView {
     var registersLazily: Bool { get }
     var usesNib: Bool { get }

Sources/DiffableCellKit/DifferentiableCellModel.swift

@@ -4,6 +4,7 @@ import CellKit
 #endif
 
 /// Support for determining whether cell model belongs to a certain cell, whether cell should be inserted, removed, updated or moved.
+@MainActor
 public protocol DifferentiableCellModel: CellModel {
 
     /// Identifier of a cell model inside it's own domain determined by reusable identifier. Assuming model is already presented inside a view, changing of this value will result in it's removal and insertion into the view.
@@ -31,14 +32,21 @@ extension DifferentiableCellModel where Self: Equatable {
 
 struct DifferentiableCellModelWrapper {
     let cellModel: DifferentiableCellModel
+    let differenceIdentifier: String
+
+    @MainActor
+    init(cellModel: DifferentiableCellModel) {
+        self.cellModel = cellModel
+        self.differenceIdentifier = "\(cellModel.reuseIdentifier)<.>\(cellModel.domainIdentifier)"
+    }
 }
 
 extension DifferentiableCellModelWrapper: Equatable, Differentiable {
     static func == (lhs: DifferentiableCellModelWrapper, rhs: DifferentiableCellModelWrapper) -> Bool {
-        lhs.cellModel.hasEqualContent(with: rhs.cellModel)
-    }
-
-    var differenceIdentifier: String {
-        "\(cellModel.reuseIdentifier)<.>\(cellModel.domainIdentifier)"
+        // DifferenceKit requires a nonisolated `==`, but wrappers are only ever created and
+        // diffed by `DifferentiableCellModelDataSource`, which is main actor-isolated.
+        MainActor.assumeIsolated {
+            lhs.cellModel.hasEqualContent(with: rhs.cellModel)
+        }
     }
 }

Sources/DiffableCellKit/DifferentiableCellModelDataSource.swift

@@ -4,6 +4,7 @@ import UIKit
 import CellKit
 #endif
 
+@MainActor
 open class DifferentiableCellModelDataSource: AbstractDataSource, DataSource {
 
     private enum Container {