Adopt Swift 6 + concurrency + remove background diffing

CHANGELOG.md

@@ -7,6 +7,14 @@ NEXT
 
 - TBA
 
+0.2.0
+-----
+
+This release closes the [0.2.0 milestone](https://github.com/jessesquires/ReactiveCollectionsKit/milestone/3?closed=1).
+
+**Breaking Changes:**
+- Adopt Swift 6 and Swift Concurrency, remove `CollectionViewDriverOptions.diffOnBackgroundQueue`. ([@jessesquires](https://github.com/jessesquires), [#157](https://github.com/jessesquires/ReactiveCollectionsKit/issues/157), [#158](https://github.com/jessesquires/ReactiveCollectionsKit/pull/158)) **See linked issue and pull request for decision to remove `diffOnBackgroundQueue`.**
+
 0.1.9
 -----
 

Example/Sources/List/ListViewController.swift

@@ -20,7 +20,6 @@ final class ListViewController: ExampleViewController, CellEventCoordinator {
     lazy var driver: CollectionViewDriver = {
         let driver = CollectionViewDriver(
             view: self.collectionView,
-            options: .init(diffOnBackgroundQueue: true),
             emptyViewProvider: sharedEmptyViewProvider,
             cellEventCoordinator: self
         )

Package.swift

@@ -41,16 +41,5 @@ let package = Package(
             ]
         )
     ],
-    swiftLanguageModes: [.v5]
+    swiftLanguageModes: [.v6]
 )
-
-#warning("Remove after Swift 6 language mode")
-let swiftSettings = [
-    SwiftSetting.enableExperimentalFeature("StrictConcurrency")
-]
-
-for target in package.targets {
-    var settings = target.swiftSettings ?? []
-    settings.append(contentsOf: swiftSettings)
-    target.swiftSettings = settings
-}

README.md

@@ -91,7 +91,7 @@ driver.update(viewModel: updated)
 ## Requirements
 
 - iOS 16.0+
-- Swift 5.10+
+- Swift 6.0+
 - Xcode 26.0+
 - [SwiftLint](https://github.com/realm/SwiftLint)
 

ReactiveCollectionsKit.xcodeproj/project.pbxproj

@@ -288,7 +288,7 @@
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = DEBUG;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_STRICT_CONCURRENCY = complete;
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VERSIONING_SYSTEM = "apple-generic";
 			};
@@ -351,7 +351,7 @@
 				SWIFT_COMPILATION_MODE = wholemodule;
 				SWIFT_OPTIMIZATION_LEVEL = "-O";
 				SWIFT_STRICT_CONCURRENCY = complete;
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 6.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VALIDATE_PRODUCT = YES;
 				VERSIONING_SYSTEM = "apple-generic";

Sources/CollectionViewDriver.swift

@@ -92,7 +92,7 @@ public final class CollectionViewDriver: NSObject {
 
         // workaround for swift initialization rules.
         // the "real" init is below.
-        self._dataSource = DiffableDataSource(view: view, diffOnBackgroundQueue: false)
+        self._dataSource = DiffableDataSource(view: view)
 
         super.init()
 
@@ -106,7 +106,6 @@ public final class CollectionViewDriver: NSObject {
         // `self` owns the `_dataSource`, so we know that `self` will always exist.
         self._dataSource = DiffableDataSource(
             view: view,
-            diffOnBackgroundQueue: options.diffOnBackgroundQueue,
             cellProvider: { [unowned self] view, indexPath, itemIdentifier in
                 self._cellProvider(
                     collectionView: view,

Sources/CollectionViewDriverOptions.swift

@@ -15,11 +15,6 @@ import Foundation
 
 /// Defines various options to customize behavior of a ``CollectionViewDriver``.
 public struct CollectionViewDriverOptions: Hashable {
-    /// Specifies whether or not to perform diffing on a background queue.
-    /// Pass `true` to perform diffing in the background,
-    /// pass `false` to perform diffing on the main thread.
-    public let diffOnBackgroundQueue: Bool
-
     /// Specifies whether or not the ``CollectionViewDriver`` should
     /// perform a hard `reloadData()` when replacing the ``CollectionViewModel`` with
     /// a new one, or if it should always perform a diff.
@@ -31,13 +26,10 @@ public struct CollectionViewDriverOptions: Hashable {
     /// Initializes a `CollectionViewDriverOptions` object.
     ///
     /// - Parameters:
-    ///   - diffOnBackgroundQueue: Whether or not to perform diffing on a background queue. Default is `false`.
     ///   - reloadDataOnReplacingViewModel: Whether or not to reload or diff during replacement. Default is `false`.
     public init(
-        diffOnBackgroundQueue: Bool = false,
         reloadDataOnReplacingViewModel: Bool = false
     ) {
-        self.diffOnBackgroundQueue = diffOnBackgroundQueue
         self.reloadDataOnReplacingViewModel = reloadDataOnReplacingViewModel
     }
 }

Sources/DebugDescriptions.swift

@@ -133,7 +133,6 @@ private func debugDescriptionBuilder<Target: TextOutputStream>(
             debugDescriptionBuilder(
                 elements: [
                     (.type(CollectionViewDriverOptions.self), indent + 2),
-                    (.field(label: "diffOnBackgroundQueue", value: options.diffOnBackgroundQueue), indent + 4),
                     (.field(label: "reloadDataOnReplacingViewModel", value: options.reloadDataOnReplacingViewModel), indent + 4),
                     (.end, indent + 2)
                 ],
@@ -203,7 +202,6 @@ func driverOptionsDebugDescription(_ options: CollectionViewDriverOptions) -> St
     debugDescriptionBuilder(
         elements: [
             (.type(CollectionViewDriverOptions.self), 0),
-            (.field(label: "diffOnBackgroundQueue", value: options.diffOnBackgroundQueue), 2),
             (.field(label: "reloadDataOnReplacingViewModel", value: options.reloadDataOnReplacingViewModel), 2),
             (.end, 0)
         ],

Sources/DiffableDataSource.swift

@@ -26,34 +26,23 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
     // Thus, unowned is safe here.
     private unowned let _collectionView: UICollectionView
 
-    private let _diffOnBackgroundQueue: Bool
-
-    private lazy var _diffingQueue = DispatchQueue(
-        label: "com.jessesquires.ReactiveCollectionsKit",
-        qos: .userInteractive,
-        autoreleaseFrequency: .workItem
-    )
-
     var logger: Logging?
 
     // MARK: Init
 
     init(
         view: UICollectionView,
-        diffOnBackgroundQueue: Bool,
         cellProvider: @escaping DiffableDataSource.CellProvider,
         supplementaryViewProvider: @escaping DiffableDataSource.SupplementaryViewProvider
     ) {
         self._collectionView = view
-        self._diffOnBackgroundQueue = diffOnBackgroundQueue
         super.init(collectionView: view, cellProvider: cellProvider)
         self.supplementaryViewProvider = supplementaryViewProvider
     }
 
-    convenience init(view: UICollectionView, diffOnBackgroundQueue: Bool) {
+    convenience init(view: UICollectionView) {
         self.init(
             view: view,
-            diffOnBackgroundQueue: diffOnBackgroundQueue,
             cellProvider: { _, _, _ in nil },
             supplementaryViewProvider: { _, _, _ in nil }
         )
@@ -66,12 +55,8 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
 
         let snapshot = DiffableSnapshot(viewModel: viewModel)
         self.applySnapshotUsingReloadData(snapshot) {
-            // UIKit guarantees `completion` is called on the main queue.
-            dispatchPrecondition(condition: .onQueue(.main))
-            MainActor.assumeIsolated {
-                completion?()
-                self.logger?.log("DataSource reload snapshot completed")
-            }
+            completion?()
+            self.logger?.log("DataSource reload snapshot completed")
         }
     }
 
@@ -89,33 +74,18 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
         // We need to inspect the current collection view state first, then pass this info downstream.
         let visibleItemIdentifiers = self._visibleItemIdentifiers()
 
-        if self._diffOnBackgroundQueue {
-            self.logger?.log("DataSource using background queue")
-            self._diffingQueue.async {
-                self._applySnapshot(
-                    from: source,
-                    to: destination,
-                    withVisibleItems: visibleItemIdentifiers,
-                    animated: animated,
-                    completion: completion
-                )
-            }
-        } else {
-            self.logger?.log("DataSource using main queue")
-            dispatchPrecondition(condition: .onQueue(.main))
-            self._applySnapshot(
-                from: source,
-                to: destination,
-                withVisibleItems: visibleItemIdentifiers,
-                animated: animated,
-                completion: completion
-            )
-        }
+        self._applySnapshot(
+            from: source,
+            to: destination,
+            withVisibleItems: visibleItemIdentifiers,
+            animated: animated,
+            completion: completion
+        )
     }
 
     // MARK: Private
 
-    nonisolated private func _applySnapshot(
+    private func _applySnapshot(
         from source: CollectionViewModel,
         to destination: CollectionViewModel,
         withVisibleItems visibleItemIdentifiers: Set<UniqueIdentifier>,
@@ -153,59 +123,49 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
         destinationSnapshot.reconfigureItems(itemsToReconfigure)
 
         // Apply the snapshot with item reconfigure updates.
-        //
-        // Swift 6 complains about 'call to main actor-isolated instance method' here.
-        // However, call this method from a background thread is valid according to the docs.
         self.apply(destinationSnapshot, animatingDifferences: animated) { [weak self] in
-            // UIKit guarantees `completion` is called on the main queue.
-            dispatchPrecondition(condition: .onQueue(.main))
-
             guard let self else {
-                MainActor.assumeIsolated {
-                    completion?()
-                }
+                completion?()
                 return
             }
 
-            MainActor.assumeIsolated {
-                // Once the snapshot with item reconfigures is applied,
-                // we need to find and apply supplementary view reconfigures, if needed.
-                //
-                // This is necessary to update all headers, footers, and supplementary views.
-                // Per notes above, supplementary views do not get reloaded / reconfigured
-                // automatically by `DiffableDataSource` when they change.
-                //
-                // To trigger updates on supplementary views with the existing APIs,
-                // the entire section must be reloaded. Yes, that sucks. We don't want to do that.
-                // That causes all items in the section to be hard-reloaded, too.
-                // Aside from the performance impact, doing that results in an ugly UI "flash"
-                // for all item cells in the collection. Gross.
-                //
-                // However, we can actually do much better than a hard reload!
-                // Instead of reloading the entire section, we can find and compare
-                // the supplementary views and manually reconfigure them if they changed.
-                //
-                // NOTE: this only matters if supplementary views are not static.
-                // That is, if they reflect data in the data source.
-                //
-                // For example, a header with a fixed title (e.g. "My Items") will NOT need to be reloaded.
-                // However, a header that displays changing data WILL need to be reloaded.
-                // (e.g. "My 10 Items")
-
-                // Check all the supplementary views and reconfigure them, if needed.
-                self._reconfigureSupplementaryViewsIfNeeded(from: source, to: destination)
-
-                // Finally, we're done and can call completion.
-                completion?()
-
-                self.logger?.log("DataSource diffing snapshot complete")
-            }
+            // Once the snapshot with item reconfigures is applied,
+            // we need to find and apply supplementary view reconfigures, if needed.
+            //
+            // This is necessary to update all headers, footers, and supplementary views.
+            // Per notes above, supplementary views do not get reloaded / reconfigured
+            // automatically by `DiffableDataSource` when they change.
+            //
+            // To trigger updates on supplementary views with the existing APIs,
+            // the entire section must be reloaded. Yes, that sucks. We don't want to do that.
+            // That causes all items in the section to be hard-reloaded, too.
+            // Aside from the performance impact, doing that results in an ugly UI "flash"
+            // for all item cells in the collection. Gross.
+            //
+            // However, we can actually do much better than a hard reload!
+            // Instead of reloading the entire section, we can find and compare
+            // the supplementary views and manually reconfigure them if they changed.
+            //
+            // NOTE: this only matters if supplementary views are not static.
+            // That is, if they reflect data in the data source.
+            //
+            // For example, a header with a fixed title (e.g. "My Items") will NOT need to be reloaded.
+            // However, a header that displays changing data WILL need to be reloaded.
+            // (e.g. "My 10 Items")
+
+            // Check all the supplementary views and reconfigure them, if needed.
+            self._reconfigureSupplementaryViewsIfNeeded(from: source, to: destination)
+
+            // Finally, we're done and can call completion.
+            completion?()
+
+            self.logger?.log("DataSource diffing snapshot complete")
         }
     }
 
     // MARK: Reconfiguring Cells
 
-    nonisolated private func _findItemsToReconfigure(
+    private func _findItemsToReconfigure(
         from source: CollectionViewModel,
         to destination: CollectionViewModel,
         withVisibleItems visibleItemIdentifiers: Set<UniqueIdentifier>

Tests/TestCollectionViewDriver.swift

@@ -430,23 +430,6 @@ final class TestCollectionViewDriver: UnitTestCase, @unchecked Sendable {
         self.waitForExpectations()
     }
 
-    @MainActor
-    func test_update_callsCompletion_withBackgroundDiffing() {
-        let driver = CollectionViewDriver(
-            view: self.collectionView,
-            options: .init(diffOnBackgroundQueue: true)
-        )
-
-        let expectation = self.expectation()
-
-        let newModel = self.fakeCollectionViewModel()
-        driver.update(viewModel: newModel, animated: true) { _ in
-            expectation.fulfillAndLog()
-        }
-
-        self.waitForExpectations()
-    }
-
     @MainActor
     func test_update_callsCompletion_withReloadOnReplace() {
         let driver = CollectionViewDriver(

Tests/TestCollectionViewDriverOptions.swift

@@ -19,7 +19,6 @@ final class TestCollectionViewDriverOptions: XCTestCase {
 
     func test_defaultValues() {
         let options = CollectionViewDriverOptions()
-        XCTAssertFalse(options.diffOnBackgroundQueue)
         XCTAssertFalse(options.reloadDataOnReplacingViewModel)
     }
 
@@ -29,21 +28,18 @@ final class TestCollectionViewDriverOptions: XCTestCase {
             options.debugDescription,
             """
             CollectionViewDriverOptions {
-              diffOnBackgroundQueue: false
               reloadDataOnReplacingViewModel: false
             }
             """
         )
 
         let options2 = CollectionViewDriverOptions(
-            diffOnBackgroundQueue: true,
             reloadDataOnReplacingViewModel: true
         )
         XCTAssertEqual(
             options2.debugDescription,
             """
             CollectionViewDriverOptions {
-              diffOnBackgroundQueue: true
               reloadDataOnReplacingViewModel: true
             }
             """

Tests/TestDebugDescriptionDriver.swift

@@ -52,7 +52,6 @@ final class TestDebugDescriptionDriver: XCTestCase {
             CollectionViewDriver \\{
               options:
                 CollectionViewDriverOptions \\{
-                  diffOnBackgroundQueue: false
                   reloadDataOnReplacingViewModel: false
                 \\}
               viewModel:
@@ -94,7 +93,6 @@ final class TestDebugDescriptionDriver: XCTestCase {
             CollectionViewDriver \\{
               options:
                 CollectionViewDriverOptions \\{
-                  diffOnBackgroundQueue: false
                   reloadDataOnReplacingViewModel: false
                 \\}
               viewModel:
@@ -155,7 +153,6 @@ final class TestDebugDescriptionDriver: XCTestCase {
             CollectionViewDriver \\{
               options:
                 CollectionViewDriverOptions \\{
-                  diffOnBackgroundQueue: false
                   reloadDataOnReplacingViewModel: false
                 \\}
               viewModel:

Tests/Utils/CollectionViewDriverOptions+Extensions.swift

@@ -16,6 +16,6 @@ import ReactiveCollectionsKit
 
 extension CollectionViewDriverOptions {
     static func test() -> Self {
-        .init(diffOnBackgroundQueue: false, reloadDataOnReplacingViewModel: true)
+        .init(reloadDataOnReplacingViewModel: true)
     }
 }