Implement debug logging for view model updates (#141)

closes #130

Author: nuomi1

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ env:
   EXAMPLE_PROJECT: Example/ExampleApp.xcodeproj
   EXAMPLE_SCHEME: ExampleApp
 
-  DEVELOPER_DIR: /Applications/Xcode_16.0.app/Contents/Developer
+  DEVELOPER_DIR: /Applications/Xcode_16.1.app/Contents/Developer
 
   IOS_DEST: "platform=iOS Simulator,name=iPhone 16,OS=latest"
 

.github/workflows/spm-ios.yml

@@ -12,7 +12,7 @@ on:
       - main
 
 env:
-  DEVELOPER_DIR: /Applications/Xcode_16.0.app/Contents/Developer
+  DEVELOPER_DIR: /Applications/Xcode_16.1.app/Contents/Developer
   IOS_DEST: "platform=iOS Simulator,name=iPhone 16,OS=latest"
   SCHEME: ReactiveCollectionsKit
 

.swiftlint.yml

@@ -111,7 +111,7 @@ analyzer_rules:
   - capture_variable
 
 line_length: 200
-file_length: 600
+file_length: 650
 
 type_body_length: 500
 function_body_length: 250

CHANGELOG.md

@@ -6,6 +6,7 @@ NEXT
 -----
 
 - Improve debug descriptions (i.e., `CustomDebugStringConvertible`) for various types. ([@nuomi1](https://github.com/nuomi1), [#139](https://github.com/jessesquires/ReactiveCollectionsKit/pull/139))
+- Implement (optional) debug logging for view model updates. You can now provide a logger for debugging purposes by setting `CollectionViewDriver.logger`. The library provides a default implementation via `RCKLogger.shared`. ([@nuomi1](https://github.com/nuomi1), [#141](https://github.com/jessesquires/ReactiveCollectionsKit/pull/141))
 - TBA
 
 0.1.8

Example/Sources/Grid/GridViewController.swift

@@ -26,9 +26,8 @@ final class GridViewController: ExampleViewController, CellEventCoordinator {
         didSet {
             // Every time the model updates, regenerate and set the view model
             let viewModel = self.makeViewModel()
-            self.driver.update(viewModel: viewModel, animated: true) {
+            self.driver.update(viewModel: viewModel, animated: true) { _ in
                 print("grid did update!")
-                print($0.viewModel)
             }
         }
     }
@@ -43,6 +42,8 @@ final class GridViewController: ExampleViewController, CellEventCoordinator {
 
     override func viewDidLoad() {
         super.viewDidLoad()
+        self.driver.logger = RCKLogger.shared
+
         let viewModel = self.makeViewModel()
         self.driver.update(viewModel: viewModel)
     }

Example/Sources/List/ListViewController.swift

@@ -36,7 +36,6 @@ final class ListViewController: ExampleViewController, CellEventCoordinator {
             Task { @MainActor in
                 await self.driver.update(viewModel: viewModel)
                 print("list did update! async")
-                print(viewModel)
             }
         }
     }
@@ -66,6 +65,7 @@ final class ListViewController: ExampleViewController, CellEventCoordinator {
 
     override func viewDidLoad() {
         super.viewDidLoad()
+        self.driver.logger = RCKLogger.shared
 
         let viewModel = self.makeViewModel()
         self.driver.update(viewModel: viewModel)

Sources/CollectionViewDriver.swift

@@ -51,6 +51,17 @@ public final class CollectionViewDriver: NSObject {
 
     private var _cachedRegistrations = Set<ViewRegistration>()
 
+    /// A debug logger to log messages that track the internal operations of the driver.
+    /// The default value is `nil`.
+    ///
+    /// - Note: You may wish to set this property to the library-provided logger, `RCKLogger.shared`.
+    ///         However, you can also provide your own implementation via the `Logging` protocol.
+    public var logger: Logging? {
+        didSet {
+            self._dataSource.logger = self.logger
+        }
+    }
+
     // MARK: Init
 
     /// Initializes a new `CollectionViewDriver`.
@@ -195,6 +206,16 @@ public final class CollectionViewDriver: NSObject {
         if self.options.reloadDataOnReplacingViewModel {
             // if given a totally new model, simply reload instead of diff
             guard new.id == old.id else {
+                self.logger?.log(
+                    """
+                    Driver will reload view model.
+                    Old:
+                    \(old.debugDescription)
+                    New:
+                    \(new.debugDescription)
+                    """
+                )
+
                 self._dataSource.reload(self.viewModel) { [weak self] in
                     // Note: UIKit guarantees this closure is called on the main queue.
                     self?._displayEmptyViewIfNeeded(animated: animated, completion: completion)
@@ -203,6 +224,16 @@ public final class CollectionViewDriver: NSObject {
             }
         }
 
+        self.logger?.log(
+            """
+            Driver will update view model.
+            Old:
+            \(old.debugDescription)
+            New:
+            \(new.debugDescription)
+            """
+        )
+
         self._dataSource.applySnapshot(
             from: old,
             to: new,

Sources/DiffableDataSource.swift

@@ -34,6 +34,8 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
         autoreleaseFrequency: .workItem
     )
 
+    var logger: Logging?
+
     // MARK: Init
 
     init(
@@ -60,12 +62,15 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
     // MARK: Applying snapshots
 
     func reload(_ viewModel: CollectionViewModel, completion: SnapshotCompletion?) {
+        self.logger?.log("DataSource will apply reload snapshot")
+
         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")
             }
         }
     }
@@ -76,13 +81,16 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
         animated: Bool,
         completion: SnapshotCompletion?
     ) {
+        self.logger?.log("DataSource will apply diffing snapshot")
+
         // Get all the currently visible items, so we can reconfigure them if needed.
         //
         // This queries the collection view for visible items, so it must happen on the main thread.
         // 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,
@@ -93,6 +101,7 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
                 )
             }
         } else {
+            self.logger?.log("DataSource using main queue")
             dispatchPrecondition(condition: .onQueue(.main))
             self._applySnapshot(
                 from: source,
@@ -188,6 +197,8 @@ final class DiffableDataSource: UICollectionViewDiffableDataSource<AnyHashable,
 
                 // Finally, we're done and can call completion.
                 completion?()
+
+                self.logger?.log("DataSource diffing snapshot complete")
             }
         }
     }

Sources/Logger.swift

@@ -0,0 +1,39 @@
+//
+//  Created by Jesse Squires
+//  https://www.jessesquires.com
+//
+//  Documentation
+//  https://jessesquires.github.io/ReactiveCollectionsKit
+//
+//  GitHub
+//  https://github.com/jessesquires/ReactiveCollectionsKit
+//
+//  Copyright © 2019-present Jesse Squires
+//
+
+import Foundation
+import OSLog
+
+/// Describes a type that logs messages for the library.
+public protocol Logging: Sendable {
+
+    /// Logs the provided message.
+    ///
+    /// - Parameter message: The message to log.
+    func log(_ message: @escaping @autoclosure () -> String)
+}
+
+/// A default ``Logging`` implementation to log debug messages.
+///
+/// You can set this logger for the ``CollectionViewDriver.logger``.
+public final class RCKLogger: Logging {
+    /// The shared logger instance.
+    public static let shared = RCKLogger()
+
+    private let _logger = Logger(subsystem: "com.jessesquires.ReactiveCollectionsKit", category: "")
+
+    /// :nodoc:
+    public func log(_ message: @escaping @autoclosure () -> String) {
+        self._logger.debug("\(message())")
+    }
+}