Swift Observation support

KMPObservableViewModelCore/ObservableKeyPath.swift

@@ -0,0 +1,38 @@
+//
+//  ObservableKeyPath.swift
+//  KMPObservableViewModelCore
+//
+//  Created by Rick Clephas on 11/06/2025.
+//
+
+import Observation
+import KMPObservableViewModelCoreObjC
+
+/// An observable `KeyPath` which uses an `ObservationRegistrar` to track changes.
+@available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+public final class ObservableKeyPath<Root: AnyObject & Observable, Value>: ViewModelKeyPath {
+
+    private weak var subject: Root?
+    private let keyPath: KeyPath<Root, Value>
+
+    /// Creates a new `ObservableKeyPath` for the provided `subject` and `keyPath`.
+    public init(_ subject: Root, _ keyPath: KeyPath<Root, Value>) {
+        self.subject = subject
+        self.keyPath = keyPath
+    }
+
+    public func access(_ publisher: any Publisher) {
+        guard let subject else { return }
+        publisher.cast().observationRegistrar.access(subject, keyPath: keyPath)
+    }
+
+    public func willSet(_ publisher: any Publisher) {
+        guard let subject else { return }
+        publisher.cast().observationRegistrar.willSet(subject, keyPath: keyPath)
+    }
+
+    public func didSet(_ publisher: any Publisher) {
+        guard let subject else { return }
+        publisher.cast().observationRegistrar.didSet(subject, keyPath: keyPath)
+    }
+}

KMPObservableViewModelCore/ObservableViewModelPublisher.swift

@@ -6,13 +6,25 @@
 //
 
 import Combine
+import Observation
 import KMPObservableViewModelCoreObjC
 
 /// Publisher for `ObservableViewModel` that connects to the `ViewModelScope`.
 public final class ObservableViewModelPublisher: Combine.Publisher, KMPObservableViewModelCoreObjC.Publisher {
     public typealias Output = Void
     public typealias Failure = Never
 
+    private var _observationRegistrar: Any? = nil
+    @available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+    public var observationRegistrar: ObservationRegistrar {
+        if let observationRegistrar = _observationRegistrar {
+            return observationRegistrar as! ObservationRegistrar
+        }
+        let observationRegistrar = ObservationRegistrar()
+        _observationRegistrar = observationRegistrar
+        return observationRegistrar
+    }
+
     internal let cancellable = ViewModelCancellable()
 
     private let publisher: ObservableObjectPublisher
@@ -33,6 +45,16 @@ public final class ObservableViewModelPublisher: Combine.Publisher, KMPObservabl
     }
 }
 
+internal extension KMPObservableViewModelCoreObjC.Publisher {
+    /// Casts this `Publisher` to an `ObservableViewModelPublisher`.
+    func cast() -> ObservableViewModelPublisher {
+        guard let publisher = self as? ObservableViewModelPublisher else {
+            fatalError("Publisher must be an ObservableViewModelPublisher")
+        }
+        return publisher
+    }
+}
+
 /// Subscriber for `ObservableViewModelPublisher` that creates `ObservableViewModelSubscription`s.
 private class ObservableViewModelSubscriber<S>: Subscriber where S : Subscriber, Never == S.Failure, Void == S.Input {
     typealias Input = Void

KMPObservableViewModelCore/PublishedKeyPath.swift

@@ -0,0 +1,28 @@
+//
+//  PublishedKeyPath.swift
+//  KMPObservableViewModelCore
+//
+//  Created by Rick Clephas on 09/06/2025.
+//
+
+import KMPObservableViewModelCoreObjC
+
+/// A published `KeyPath` which uses an `ObservableObject` to emit change events.
+public final class PublishedKeyPath: ViewModelKeyPath {
+
+    public static let shared = PublishedKeyPath()
+
+    private init() { }
+
+    public func access(_ publisher: any Publisher) {
+        // Published keyPaths only emit on willSet
+    }
+
+    public func willSet(_ publisher: any Publisher) {
+        publisher.cast().send()
+    }
+
+    public func didSet(_ publisher: any Publisher) {
+        // Published keyPaths only emit on willSet
+    }
+}

KMPObservableViewModelCore/ViewModel.swift

@@ -22,7 +22,7 @@ public protocol ViewModel: ObservableObject where ObjectWillChangePublisher == O
 public extension ViewModel {
     var viewModelWillChange: ObservableViewModelPublisher {
         if let publisher = viewModelScope.publisher {
-            return publisher as! ObservableViewModelPublisher
+            return publisher.cast()
         }
         let publisher = ObservableViewModelPublisher(self)
         viewModelScope.publisher = publisher

KMPObservableViewModelCoreObjC/KMPOVMViewModelKeyPath.h

@@ -0,0 +1,25 @@
+//
+//  KMPOVMViewModelKeyPath.h
+//  KMPObservableViewModelCoreObjC
+//
+//  Created by Rick Clephas on 11/06/2025.
+//
+
+#ifndef KMPOVMViewModelKeyPath_h
+#define KMPOVMViewModelKeyPath_h
+
+#import <Foundation/Foundation.h>
+#import "KMPOVMPublisher.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+__attribute__((swift_name("ViewModelKeyPath")))
+@protocol KMPOVMViewModelKeyPath
+- (void)access:(id<KMPOVMPublisher>)publisher;
+- (void)willSet:(id<KMPOVMPublisher>)publisher;
+- (void)didSet:(id<KMPOVMPublisher>)publisher;
+@end
+
+NS_ASSUME_NONNULL_END
+
+#endif /* KMPOVMViewModelKeyPath_h */

KMPObservableViewModelCoreObjC/KMPObservableViewModelCoreObjC.h

@@ -7,4 +7,5 @@
 
 #import "KMPOVMPublisher.h"
 #import "KMPOVMSubscriptionCount.h"
+#import "KMPOVMViewModelKeyPath.h"
 #import "KMPOVMViewModelScope.h"

KMPObservableViewModelPlugin/KMPObservableViewModelPlugin.swift

@@ -0,0 +1,16 @@
+//
+//  KMPObservableViewModelPlugin.swift
+//  KMPObservableViewModelPlugin
+//
+//  Created by Rick Clephas on 21/06/2025.
+//
+
+import SwiftCompilerPlugin
+import SwiftSyntaxMacros
+
+@main
+struct KMPObservableViewModelPlugin: CompilerPlugin {
+    var providingMacros: [any Macro.Type] = [
+        ObservableViewModel.self
+    ]
+}

KMPObservableViewModelPlugin/ObservableViewModel.swift

@@ -0,0 +1,56 @@
+//
+//  ObservableViewModel.swift
+//  KMPObservableViewModelPlugin
+//
+//  Created by Rick Clephas on 21/06/2025.
+//
+
+import SwiftSyntax
+import SwiftSyntaxMacros
+import SwiftSyntaxMacroExpansion
+
+public struct ObservableViewModel: MemberMacro {
+    public static func expansion(
+        of node: AttributeSyntax,
+        providingMembersOf declaration: some DeclGroupSyntax,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+    ) throws -> [DeclSyntax] {
+        guard let declaration = declaration.as(ExtensionDeclSyntax.self) else {
+            throw MacroExpansionErrorMessage("@ObservableViewModel can only be applied to an extension")
+        }
+        guard protocols.isEmpty else {
+            throw MacroExpansionErrorMessage("@ObservableViewModel type must be of type ViewModel")
+        }
+        let type = declaration.extendedType
+        return [
+            """
+            public subscript<Value>(dynamicMember keyPath: KeyPath<\(type.trimmed).Properties, Value>) -> Value {
+                if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *) {
+                    __properties[observable: keyPath]
+                } else {
+                    __properties[published: keyPath]
+                }
+            }
+            """,
+            """
+            public subscript<Value>(dynamicMember keyPath: ReferenceWritableKeyPath<\(type.trimmed).Properties, Value>) -> Value {
+                get {
+                    if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *) {
+                        __properties[observable: keyPath]
+                    } else {
+                        __properties[published: keyPath]
+                    }
+                }
+                set {
+                    if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *) {
+                        __properties[observable: keyPath] = newValue
+                    } else {
+                        __properties[published: keyPath] = newValue
+                    }
+                }
+            }
+            """
+        ]
+    }
+}

KMPObservableViewModelProperties/ObservableProperties.swift

@@ -0,0 +1,45 @@
+//
+//  Properties.swift
+//  KMPObservableViewModelProperties
+//
+//  Created by Rick Clephas on 10/06/2025.
+//
+
+import Foundation
+import Observation
+import KMPObservableViewModelCore
+
+/// A class that stores all `ObservableKeyPath` properties of a ViewModel.
+@available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+public protocol ObservableProperties: Properties, Observable { }
+
+@available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+public extension ObservableProperties {
+
+    /// Returns the value of a property ensuring the `keyPath` is being registered.
+    subscript<Value>(observable keyPath: KeyPath<Self, Value>) -> Value {
+        let value = self[keyPath: keyPath]
+        guard shouldRegisterKeyPath(), Thread.isMainThread else { return value }
+        registerKeyPath(ObservableKeyPath(self, keyPath))
+        return self[keyPath: keyPath]
+    }
+
+    /// Gets or sets the value of a property ensuring the `keyPath` is being registered.
+    subscript<Value>(observable keyPath: ReferenceWritableKeyPath<Self, Value>) -> Value {
+        get { self[observable: keyPath as KeyPath<Self, Value>] }
+        set { self[keyPath: keyPath] = newValue }
+    }
+
+    /// `PublishedProperties` implementation required for compilation if only `ObservableProperties` is used.
+    @_disfavoredOverload
+    subscript<Value>(published keyPath: KeyPath<Self, Value>) -> Value {
+        self[observable: keyPath]
+    }
+
+    /// `PublishedProperties` implementation required for compilation if only `ObservableProperties` is used.
+    @_disfavoredOverload
+    subscript<Value>(published keyPath: ReferenceWritableKeyPath<Self, Value>) -> Value {
+        get { self[observable: keyPath] }
+        set { self[observable: keyPath] = newValue }
+    }
+}

KMPObservableViewModelProperties/ObservableViewModel.swift

@@ -0,0 +1,9 @@
+//
+//  ObservableViewModel.swift
+//  KMPObservableViewModelProperties
+//
+//  Created by Rick Clephas on 21/06/2025.
+//
+
+@attached(member, conformances: ViewModel, names: named(subscript(dynamicMember:)))
+public macro ObservableViewModel() = #externalMacro(module: "KMPObservableViewModelPlugin", type: "ObservableViewModel")

KMPObservableViewModelProperties/Properties.swift

@@ -0,0 +1,14 @@
+//
+//  Properties.swift
+//  KMPObservableViewModelProperties
+//
+//  Created by Rick Clephas on 16/06/2025.
+//
+
+import KMPObservableViewModelCoreObjC
+
+/// A class that stores all observable properties of a ViewModel.
+public protocol Properties: AnyObject {
+    func shouldRegisterKeyPath() -> Bool
+    func registerKeyPath(_ keyPath: any ViewModelKeyPath)
+}

KMPObservableViewModelProperties/PublishedProperties.swift

@@ -0,0 +1,43 @@
+//
+//  Properties.swift
+//  KMPObservableViewModelProperties
+//
+//  Created by Rick Clephas on 10/06/2025.
+//
+
+import Foundation
+import Combine
+import KMPObservableViewModelCore
+
+/// A class that stores all `PublishedKeyPath` properties of a ViewModel.
+public protocol PublishedProperties: Properties { }
+
+public extension PublishedProperties {
+
+    /// Returns the value of a property ensuring the `keyPath` is being registered.
+    subscript<Value>(published keyPath: KeyPath<Self, Value>) -> Value {
+        let value = self[keyPath: keyPath]
+        guard shouldRegisterKeyPath(), Thread.isMainThread else { return value }
+        registerKeyPath(PublishedKeyPath.shared)
+        return self[keyPath: keyPath]
+    }
+
+    /// Gets or sets the value of a property ensuring the `keyPath` is being registered.
+    subscript<Value>(published keyPath: ReferenceWritableKeyPath<Self, Value>) -> Value {
+        get { self[published: keyPath as KeyPath<Self, Value>] }
+        set { self[keyPath: keyPath] = newValue }
+    }
+
+    /// `ObservableProperties` implementation required for compilation if only `PublishedProperties` is used.
+    @_disfavoredOverload
+    subscript<Value>(observable keyPath: KeyPath<Self, Value>) -> Value {
+        self[published: keyPath]
+    }
+
+    /// `ObservableProperties` implementation required for compilation if only `PublishedProperties` is used.
+    @_disfavoredOverload
+    subscript<Value>(observable keyPath: ReferenceWritableKeyPath<Self, Value>) -> Value {
+        get { self[published: keyPath] }
+        set { self[published: keyPath] = newValue }
+    }
+}

KMPObservableViewModelProperties/ViewModel.swift

@@ -0,0 +1,18 @@
+//
+//  ViewModel.swift
+//  KMPObservableViewModelProperties
+//
+//  Created by Rick Clephas on 11/06/2025.
+//
+
+import KMPObservableViewModelCore
+
+/// A Kotlin Multiplatform ViewModel.
+@dynamicMemberLookup
+public protocol ViewModel: KMPObservableViewModelCore.ViewModel { }
+
+private extension ViewModel {
+    subscript<T>(dynamicMember keyPath: KeyPath<Properties, T>) -> T {
+        fatalError("ViewModel subscripts will be added by @ObservableViewModel")
+    }
+}