Disable syncing from local if its default after `iCloud.add` (#185)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

Sources/Defaults/Defaults+iCloud.swift

@@ -39,7 +39,7 @@ extension Defaults {
 
 	## Dynamically Toggle Syncing
 
-	You can also toggle the syncing behavior dynamically using the ``Defaults/iCloud/add(_:)-5gffb`` and ``Defaults/iCloud/remove(_:)-1b8w5`` methods.
+	You can also toggle the syncing behavior dynamically using the ``Defaults/iCloud/add(_:)`` and ``Defaults/iCloud/remove(_:)-1b8w5`` methods.
 
 	```swift
 	import Defaults
@@ -82,15 +82,10 @@ extension Defaults {
 		/**
 		Add the keys to be automatically synced.
 		*/
-		public static func add(_ keys: Defaults.Keys...) {
-			synchronizer.add(keys)
-		}
-
-		/**
-		Add the keys to be automatically synced.
-		*/
-		public static func add(_ keys: [Defaults.Keys]) {
-			synchronizer.add(keys)
+		// TODO: Support array of Defaults.Key after Swift 6 pack iteration is supported.
+		// https://github.com/sindresorhus/Defaults/pull/185#discussion_r1704464183
+		public static func add<each Value: Defaults.Serializable>(_ keys: repeat Defaults.Key<each Value>) {
+			repeat synchronizer.add(each keys)
 		}
 
 		/**
@@ -269,11 +264,23 @@ final class iCloudSynchronizer {
 	/**
 	Add new key and start to observe its changes.
 	*/
-	func add(_ keys: [Defaults.Keys]) {
-		self.keys.formUnion(keys)
-		syncWithoutWaiting(keys)
-		for key in keys {
+	func add<Value: Defaults.Serializable>(_ key: Defaults.Key<Value>) {
+		let (isInserted, _) = self.keys.insert(key)
+		guard isInserted else {
+			return
+		}
+
 		localKeysMonitor.add(key: key)
+
+		// If the local value is the default value, only sync from remote, since all devices should already have the default value.
+		if key._isDefaultValue {
+			guard case .remote = latestDataSource(forKey: key) else {
+				return
+			}
+
+			syncWithoutWaiting([key], .remote)
+		} else {
+			syncWithoutWaiting([key])
 		}
 	}
 

Sources/Defaults/Defaults.swift

@@ -187,6 +187,31 @@ extension Defaults.Key {
 	) where Value == T? {
 		self.init(name, default: nil, suite: suite, iCloud: iCloud)
 	}
+
+	/**
+	Check whether the stored value is the default value.
+
+	- Note: This is only for internal use because it would not work for non-equatable values.
+	*/
+	var _isDefaultValue: Bool {
+		let defaultValue = defaultValue
+		let value = suite[self]
+		guard
+			let defaultValue = defaultValue as? any Equatable,
+			let value = value as? any Equatable
+		else {
+			return false
+		}
+
+		return defaultValue.isEqual(value)
+	}
+}
+
+extension Defaults.Key where Value: Equatable {
+	/**
+	Check whether the stored value is the default value.
+	*/
+	public var isDefaultValue: Bool { self._isDefaultValue }
 }
 
 extension Defaults {

Sources/Defaults/Utilities.swift

@@ -165,6 +165,19 @@ extension Collection {
 	}
 }
 
+extension Equatable {
+	func isEqual(_ rhs: any Equatable) -> Bool {
+		guard
+			let rhs = rhs as? Self,
+			rhs == self
+		else {
+			return false
+		}
+
+		return true
+	}
+}
+
 extension Defaults {
 	@usableFromInline
 	static func isValidKeyPath(name: String) -> Bool {

Tests/DefaultsTests/Defaults+iCloudTests.swift

@@ -88,14 +88,12 @@ final class DefaultsICloudTests: XCTestCase {
 	}
 
 	func testICloudInitialize() async {
-		print(Defaults.iCloud.keys)
 		let name = Defaults.Key<String>("testICloudInitialize_name", default: "0", iCloud: true)
 		let quality = Defaults.Key<Double>("testICloudInitialize_quality", default: 0.0, iCloud: true)
 
-		print(Defaults.iCloud.keys)
 		await Defaults.iCloud.waitForSyncCompletion()
-		XCTAssertEqual(mockStorage.data(forKey: name.name), "0")
-		XCTAssertEqual(mockStorage.data(forKey: quality.name), 0.0)
+		XCTAssertNil(mockStorage.data(forKey: name.name))
+		XCTAssertNil(mockStorage.data(forKey: quality.name))
 		let name_expected = ["1", "2", "3", "4", "5", "6", "7"]
 		let quality_expected = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]
 
@@ -251,8 +249,9 @@ final class DefaultsICloudTests: XCTestCase {
 
 	func testAddFromDetached() async {
 		let name = Defaults.Key<String>("testInitAddFromDetached_name", default: "0")
+		let quantity = Defaults.Key<Bool>("testInitAddFromDetached_quantity", default: false)
 		let task = Task.detached {
-			Defaults.iCloud.add(name)
+			Defaults.iCloud.add(name, quantity)
 			Defaults.iCloud.syncWithoutWaiting()
 			await Defaults.iCloud.waitForSyncCompletion()
 		}
@@ -268,7 +267,7 @@ final class DefaultsICloudTests: XCTestCase {
 			let name = Defaults.Key<String>("testICloudInitializeFromDetached_name", default: "0", iCloud: true)
 
 			await Defaults.iCloud.waitForSyncCompletion()
-			XCTAssertEqual(mockStorage.data(forKey: name.name), "0")
+			XCTAssertNil(mockStorage.data(forKey: name.name))
 		}
 		await task.value
 	}

Tests/DefaultsTests/DefaultsTests.swift

@@ -177,6 +177,13 @@ final class DefaultsTests: XCTestCase {
 		Defaults.removeAll(suite: customSuite)
 	}
 
+	func testIsDefaultValue() {
+		let key = Defaults.Key<Bool>("isDefaultValue", default: false)
+		XCTAssert(key.isDefaultValue)
+		Defaults[key].toggle()
+		XCTAssert(!key.isDefaultValue)
+	}
+
 	func testObserveKeyCombine() {
 		let key = Defaults.Key<Bool>("observeKey", default: false)
 		let expect = expectation(description: "Observation closure being called")