Fix infinite recursion in @ObservableDefault with mutating methods

Fixes #217

Author: sindresorhus

Sources/DefaultsMacrosDeclarations/ObservableDefaultMacro.swift

@@ -27,6 +27,9 @@ extension ObservableDefaultMacro: AccessorMacro {
 		// The get accessor also sets up an observation to update the value when the UserDefaults
 		// changes from elsewhere. Doing so requires attaching it as an Objective-C associated
 		// object due to limitations with current macro capabilities and Swift concurrency.
+		//
+		// To prevent infinite recursion when the setter triggers the observation handler,
+		// we use Defaults.withoutPropagation to suppress observer callbacks during the write.
 		return [
 			#"""
 			get {
@@ -44,7 +47,9 @@ extension ObservableDefaultMacro: AccessorMacro {
 			#"""
 			set {
 				withMutation(keyPath: \.\#(property)) {
-					Defaults[\#(expression)] = newValue
+					Defaults.withoutPropagation {
+						Defaults[\#(expression)] = newValue
+					}
 				}
 			}
 			"""#

Tests/DefaultsMacrosTests/ObservableDefaultTests.swift

@@ -12,9 +12,12 @@ private let colorKey = "colorKey"
 private let defaultColor = "blue"
 private let newColor = "purple"
 
+private let testSetKey = "testSetKey"
+
 extension Defaults.Keys {
 	static let animal = Defaults.Key(animalKey, default: defaultAnimal)
 	static let color = Defaults.Key(colorKey, default: defaultColor)
+	static let testSet = Defaults.Key(testSetKey, default: Set<Int>())
 }
 
 func getKey() -> Defaults.Key<String> {
@@ -67,12 +70,21 @@ private final class TestModelWithMultipleValues {
 	var color: String
 }
 
+@available(macOS 14, iOS 17, tvOS 17, watchOS 10, visionOS 1, *)
+@Observable
+private final class TestModelWithSet {
+	@ObservableDefault(.testSet)
+	@ObservationIgnored
+	var testSet: Set<Int>
+}
+
 @Suite(.serialized)
 final class ObservableDefaultTests {
 	init() {
 		Defaults.removeAll()
 		Defaults[.animal] = defaultAnimal
 		Defaults[.color] = defaultColor
+		Defaults[.testSet] = []
 	}
 
 	deinit {
@@ -194,4 +206,17 @@ final class ObservableDefaultTests {
 		#expect(model.animal == newAnimal)
 		#expect(model.color == newColor)
 	}
+
+	@available(macOS 14, iOS 17, tvOS 17, watchOS 10, visionOS 1, *)
+	@Test
+	func testMacroWithSetNoInfiniteRecursion() async {
+		let model = TestModelWithSet()
+		#expect(model.testSet == [])
+
+		// This should not cause infinite recursion
+		model.testSet.formUnion(1...10)
+
+		#expect(model.testSet == Set(1...10))
+		#expect(Defaults[.testSet] == Set(1...10))
+	}
 }