Refactor InMemoryStorage

Sources/CoreModel/InMemoryStorage.swift

@@ -6,29 +6,21 @@
 //  Copyright © 2026 PureSwift. All rights reserved.
 //
 
-#if !hasFeature(Embedded)
-import Synchronization
-#endif
-
 /// Shared in-memory backing store.
 ///
 /// Holds the objects and registered functions for an ``InMemoryModelStorage`` and,
 /// optionally, one or more ``InMemoryViewContext`` values. Because the backing is a
 /// reference type, a store and a view context that share the same instance observe
 /// the exact same data.
 ///
-/// The type is thread-safe: the mutable state lives inside a `Mutex`, so the
-/// actor-isolated ``InMemoryModelStorage`` and the main-actor ``InMemoryViewContext``
-/// can operate on the same instance concurrently. Under Embedded Swift the mutex is
-/// elided: with a concurrency runtime the backing is only ever touched from within its
+/// The type is thread-safe: the mutable state lives behind a ``Locked`` (a `Mutex`
+/// where the runtime has one, `NSLock` on older Darwin), so the sendable
+/// ``InMemoryModelStorage`` and the main-actor ``InMemoryViewContext`` can operate
+/// on the same instance concurrently. Under Embedded Swift the lock is elided:
+/// with a concurrency runtime the backing is only ever touched from within its
 /// owning actor, and without one (e.g. bare-metal ARM, where ``ModelStorage``
 /// itself is unavailable) this synchronous store is the storage API, used
 /// directly from the single-threaded main loop.
-///
-/// - Note: On Apple platforms this type is gated on the availability of
-///   `Synchronization.Mutex`, which is not back-deployed. The rest of `CoreModel`
-///   keeps the package's lower deployment targets.
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 internal final class InMemoryStorage {
 
     /// The schema entities are validated against.
@@ -45,7 +37,7 @@ internal final class InMemoryStorage {
     #if hasFeature(Embedded)
     private var state = State()
     #else
-    private let state = Mutex(State())
+    private let state = Locked(State())
     #endif
 
     public init(model: Model) {
@@ -56,7 +48,7 @@ internal final class InMemoryStorage {
         #if hasFeature(Embedded)
         return try body(&state)
         #else
-        return try state.withLock { (state) throws(E) in
+        return try state.withValue { (state) throws(E) in
             try body(&state)
         }
         #endif
@@ -220,11 +212,9 @@ internal final class InMemoryStorage {
 #if hasFeature(Embedded)
 // - Note: Safe because the backing is confined to the owning actor, or to the
 //   single-threaded main loop on targets without a concurrency runtime.
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 extension InMemoryStorage: @unchecked Sendable {}
 #else
 // - Note: Checked: `model` is an immutable `Sendable` value and every piece of
-//   mutable state lives inside the `Mutex`.
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
+//   mutable state lives inside the ``Locked``.
 extension InMemoryStorage: Sendable {}
 #endif

Sources/CoreModel/InMemoryStore.swift

@@ -22,10 +22,6 @@
 ///
 /// On platforms that support it, ``viewContext`` returns a synchronous,
 /// main-actor ``InMemoryViewContext`` backed by the same data.
-///
-/// - Note: Inherits ``InMemoryStorage``'s Apple-platform availability, which is
-///   gated on `Synchronization.Mutex`.
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 public actor InMemoryModelStorage {
 
     internal let backing: InMemoryStorage
@@ -94,7 +90,6 @@ public actor InMemoryModelStorage {
 // MARK: - ViewContext
 
 #if !hasFeature(Embedded)
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 public extension InMemoryModelStorage {
 
     /// A synchronous, main-actor view context backed by the same data as this store.
@@ -121,7 +116,6 @@ public extension InMemoryModelStorage {
 //   `CoreModelError` to `any Error` is disallowed (`#EmbeddedRestrictions`).
 //   Embedded consumers call the store's methods directly; they provide the
 //   same API with typed throws.
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 extension InMemoryModelStorage: ModelStorage {}
 #endif
 

Sources/CoreModel/InMemoryViewContext.swift

@@ -22,10 +22,6 @@
 ///
 /// Useful for SwiftUI previews, unit tests, and lightweight main-thread caches
 /// where the `async` ``InMemoryModelStorage`` would be inconvenient.
-///
-/// - Note: Inherits ``InMemoryStorage``'s Apple-platform availability, which is
-///   gated on `Synchronization.Mutex`.
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 @MainActor
 public final class InMemoryViewContext {
 
@@ -94,7 +90,6 @@ public final class InMemoryViewContext {
 
 // MARK: - ViewContext
 
-@available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
 extension InMemoryViewContext: ViewContext {}
 
 #endif

Sources/CoreModel/Locked.swift

@@ -0,0 +1,124 @@
+//
+//  Locked.swift
+//  CoreModel
+//
+//  Created by Alsey Coleman Miller on 7/21/26.
+//  Copyright © 2026 PureSwift. All rights reserved.
+//
+
+// - Note: Unavailable under Embedded Swift — the types that would use it there
+//   (``InMemoryStorage``) elide the lock entirely, since state is confined to the
+//   owning actor or the single-threaded main loop.
+#if !hasFeature(Embedded)
+
+#if canImport(Darwin)
+import Foundation
+#endif
+import Synchronization
+
+/// Mutable state behind a lock.
+///
+/// Lets a class expose `Sendable` thread-safe access to mutable state without
+/// raising the package's deployment targets to where `Synchronization.Mutex`
+/// became available.
+///
+/// Backed by `Mutex` wherever the runtime has it (non-Darwin, and Darwin at or above
+/// iOS 18 / macOS 15), falling back to `NSLock` on the older Darwin releases this
+/// package still deploys to.
+internal final class Locked<Value>: Sendable {
+
+    // `@available` isn't allowed on enum cases with associated values, and naming the
+    // Mutex-backed class in a payload would require it — so that payload is stored
+    // erased and downcast behind the same availability check that constructed it.
+    private enum Storage: @unchecked Sendable {
+        case mutex(AnyObject)
+        #if canImport(Darwin)
+        case nsLock(NSLockStorage<Value>)
+        #endif
+    }
+
+    private let storage: Storage
+
+    public init(_ value: Value) {
+        #if canImport(Darwin)
+        if #available(iOS 18, macOS 15, watchOS 11, tvOS 18, visionOS 2, *) {
+            self.storage = .mutex(MutexStorage(value))
+        } else {
+            self.storage = .nsLock(NSLockStorage(value))
+        }
+        #else
+        self.storage = .mutex(MutexStorage(value))
+        #endif
+    }
+
+    public var value: Value {
+        withValue { $0 }
+    }
+
+    @discardableResult
+    public func withValue<Result, Failure: Error>(
+        _ body: (inout Value) throws(Failure) -> Result
+    ) throws(Failure) -> Result {
+        switch storage {
+        case .mutex(let storage):
+            guard #available(iOS 18, macOS 15, watchOS 11, tvOS 18, visionOS 2, *) else {
+                fatalError("Mutex storage constructed on an OS without the Synchronization runtime")
+            }
+            return try unsafeDowncast(storage, to: MutexStorage<Value>.self).withValue(body)
+        #if canImport(Darwin)
+        case .nsLock(let storage):
+            return try storage.withValue(body)
+        #endif
+        }
+    }
+}
+
+// MARK: - Storage
+
+@available(iOS 18, macOS 15, watchOS 11, tvOS 18, visionOS 2, *)
+private final class MutexStorage<Value>: Sendable {
+
+    // `Mutex` requires `sending` values in and out; `Locked` predates that and promises
+    // only what `NSLock` did. The wrapper opts out of the transfer checking so both
+    // backends expose identical semantics.
+    private struct UncheckedSendable<Wrapped>: @unchecked Sendable {
+        var wrapped: Wrapped
+    }
+
+    private let mutex: Mutex<UncheckedSendable<Value>>
+
+    init(_ value: Value) {
+        self.mutex = Mutex(UncheckedSendable(wrapped: value))
+    }
+
+    func withValue<Result, Failure: Error>(
+        _ body: (inout Value) throws(Failure) -> Result
+    ) throws(Failure) -> Result {
+        try mutex.withLock { (state: inout UncheckedSendable<Value>) throws(Failure) -> UncheckedSendable<Result> in
+            UncheckedSendable(wrapped: try body(&state.wrapped))
+        }.wrapped
+    }
+}
+
+#if canImport(Darwin)
+private final class NSLockStorage<Value>: @unchecked Sendable {
+
+    private let lock = NSLock()
+
+    private var value: Value
+
+    init(_ value: Value) {
+        self.value = value
+    }
+
+    func withValue<Result, Failure: Error>(
+        _ body: (inout Value) throws(Failure) -> Result
+    ) throws(Failure) -> Result {
+        lock.lock()
+        defer { lock.unlock() }
+        return try body(&value)
+    }
+}
+#endif
+
+#endif

Tests/CoreModelTests/InMemoryStoreTests.swift

@@ -16,7 +16,6 @@ import Testing
         EntityDescription(entity: Event.self)
     ])
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func insertAndFetch() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let person = Person(name: "Alice", age: 30)
@@ -28,7 +27,6 @@ import Testing
         #expect(missing == nil)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func update() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         var person = Person(name: "Alice", age: 30)
@@ -41,7 +39,6 @@ import Testing
         #expect(count == 1)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func batchInsert() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let people = (1...10).map { Person(name: "Person \($0)", age: UInt(20 + $0)) }
@@ -50,7 +47,6 @@ import Testing
         #expect(count == 10)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func fetchRequest() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let people = (1...5).map { Person(name: "Person \($0)", age: UInt(20 + $0)) }
@@ -81,7 +77,6 @@ import Testing
         #expect(count == 2)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func fetchID() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let person = Person(name: "Alice", age: 30)
@@ -90,7 +85,6 @@ import Testing
         #expect(ids == [ObjectID(person.id)])
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func delete() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let people = (1...3).map { Person(name: "Person \($0)", age: UInt(20 + $0)) }
@@ -104,7 +98,6 @@ import Testing
         #expect(count == 0)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func relationshipPredicate() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let event = Event(name: "WWDC", date: Date())
@@ -118,7 +111,6 @@ import Testing
         #expect(attendees == [attendee])
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func customFunction() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let stringLength = DatabaseFunction(name: "LENGTH", argumentCount: 1) { arguments in
@@ -144,7 +136,6 @@ import Testing
         #expect(longNames.map { $0.name } == ["Alexandra"])
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func modelValidation() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let person = Person(name: "Alice", age: 30)

Tests/CoreModelTests/InMemoryViewContextTests.swift

@@ -17,7 +17,6 @@ import Testing
         EntityDescription(entity: Event.self)
     ])
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func insertAndFetch() throws {
         let context = InMemoryViewContext(model: Self.model)
         let person = Person(name: "Alice", age: 30)
@@ -29,7 +28,6 @@ import Testing
         #expect(missing == nil)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func update() throws {
         let context = InMemoryViewContext(model: Self.model)
         var person = Person(name: "Alice", age: 30)
@@ -42,7 +40,6 @@ import Testing
         #expect(count == 1)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func batchInsert() throws {
         let context = InMemoryViewContext(model: Self.model)
         let people = (1...10).map { Person(name: "Person \($0)", age: UInt(20 + $0)) }
@@ -51,7 +48,6 @@ import Testing
         #expect(count == 10)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func fetchRequest() throws {
         let context = InMemoryViewContext(model: Self.model)
         let people = (1...5).map { Person(name: "Person \($0)", age: UInt(20 + $0)) }
@@ -82,7 +78,6 @@ import Testing
         #expect(count == 2)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func fetchID() throws {
         let context = InMemoryViewContext(model: Self.model)
         let person = Person(name: "Alice", age: 30)
@@ -91,7 +86,6 @@ import Testing
         #expect(ids == [ObjectID(person.id)])
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func delete() throws {
         let context = InMemoryViewContext(model: Self.model)
         let people = (1...3).map { Person(name: "Person \($0)", age: UInt(20 + $0)) }
@@ -105,7 +99,6 @@ import Testing
         #expect(count == 0)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func relationshipPredicate() throws {
         let context = InMemoryViewContext(model: Self.model)
         let event = Event(name: "WWDC", date: Date())
@@ -119,7 +112,6 @@ import Testing
         #expect(attendees == [attendee])
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func customFunction() throws {
         let context = InMemoryViewContext(model: Self.model)
         let stringLength = DatabaseFunction(name: "LENGTH", argumentCount: 1) { arguments in
@@ -145,7 +137,6 @@ import Testing
         #expect(longNames.map { $0.name } == ["Alexandra"])
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func sharedDataWithStore() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let context = store.viewContext
@@ -167,7 +158,6 @@ import Testing
         #expect(try context.count(FetchRequest(entity: Person.entityName)) == 1)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func concurrentAccessWithStore() async throws {
         let store = InMemoryModelStorage(model: Self.model)
         let context = store.viewContext
@@ -190,7 +180,6 @@ import Testing
         #expect(count == 100)
     }
 
-    @available(macOS 15, iOS 18, tvOS 18, watchOS 11, visionOS 2, *)
     @Test func modelValidation() throws {
         let context = InMemoryViewContext(model: Self.model)
         let person = Person(name: "Alice", age: 30)