Modern concurrency support (#175)

* Add @mainactor and Sendable annotations

Enable strict concurrency

Get backends to compile and update GTK backends

Mac-specific fixes

More sendability improvements (please tell me this compiles on Windows)

I love waiting 15 minutes for CI to compile a 1-line change

* Make Image Sendable

use concurrency-annotated version of ImageFormats

* Post-rebase fixes

* Add more mainactor annotations to windows

Author: bbrk24

Package.resolved

@@ -96,7 +96,7 @@ let package = Package(
         ),
         .package(
             url: "https://github.com/stackotter/swift-image-formats",
-            .upToNextMinor(from: "0.3.2")
+            .upToNextMinor(from: "0.3.3")
         ),
         .package(
             url: "https://github.com/stackotter/swift-windowsappsdk",
@@ -138,6 +138,9 @@ let package = Package(
                 "Views/TupleViewChildren.swift.gyb",
                 "Views/TableRowContent.swift.gyb",
                 "Scenes/TupleScene.swift.gyb",
+            ],
+            swiftSettings: [
+                .enableUpcomingFeature("StrictConcurrency")
             ]
         ),
         .testTarget(

Package.swift

@@ -44,7 +44,7 @@ public final class AppKitBackend: AppBackend {
         NSApplication.shared.delegate = appDelegate
     }
 
-    public func runMainLoop(_ callback: @escaping () -> Void) {
+    public func runMainLoop(_ callback: @escaping @MainActor () -> Void) {
         callback()
         NSApplication.shared.activate(ignoringOtherApps: true)
         NSApplication.shared.run()
@@ -316,7 +316,7 @@ public final class AppKitBackend: AppBackend {
         NSApplication.shared.helpMenu = helpMenu
     }
 
-    public func runInMainThread(action: @escaping () -> Void) {
+    public func runInMainThread(action: @escaping @MainActor () -> Void) {
         DispatchQueue.main.async {
             action()
         }

Sources/AppKitBackend/AppKitBackend.swift

@@ -64,7 +64,7 @@ public final class Gtk3Backend: AppBackend {
         gtkApp.registerSession = true
     }
 
-    public func runMainLoop(_ callback: @escaping () -> Void) {
+    public func runMainLoop(_ callback: @escaping @MainActor () -> Void) {
         gtkApp.run { window in
             self.precreatedWindow = window
             callback()
@@ -344,14 +344,14 @@ public final class Gtk3Backend: AppBackend {
     }
 
     class ThreadActionContext {
-        var action: () -> Void
+        var action: @MainActor () -> Void
 
-        init(action: @escaping () -> Void) {
+        init(action: @escaping @MainActor () -> Void) {
             self.action = action
         }
     }
 
-    public func runInMainThread(action: @escaping () -> Void) {
+    public func runInMainThread(action: @escaping @MainActor () -> Void) {
         let action = ThreadActionContext(action: action)
         g_idle_add_full(
             0,
@@ -360,9 +360,11 @@ public final class Gtk3Backend: AppBackend {
                     fatalError("Gtk action callback called without context")
                 }
 
-                let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
-                    .takeUnretainedValue()
-                action.action()
+                MainActor.assumeIsolated {
+                    let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
+                        .takeUnretainedValue()
+                    action.action()
+                }
 
                 return 0
             },
@@ -384,9 +386,11 @@ public final class Gtk3Backend: AppBackend {
                     fatalError("Gtk action callback called without context")
                 }
 
-                let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
-                    .takeUnretainedValue()
-                action.action()
+                MainActor.assumeIsolated {
+                    let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
+                        .takeUnretainedValue()
+                    action.action()
+                }
 
                 // Cancel the recurring timeout after one iteration
                 return 0

Sources/Gtk3Backend/Gtk3Backend.swift

@@ -65,7 +65,7 @@ public final class GtkBackend: AppBackend {
 
     var globalCSSProvider: CSSProvider?
 
-    public func runMainLoop(_ callback: @escaping () -> Void) {
+    public func runMainLoop(_ callback: @escaping @MainActor () -> Void) {
         gtkApp.run { window in
             self.precreatedWindow = window
             callback()
@@ -315,14 +315,14 @@ public final class GtkBackend: AppBackend {
     }
 
     class ThreadActionContext {
-        var action: () -> Void
+        var action: @MainActor () -> Void
 
-        init(action: @escaping () -> Void) {
+        init(action: @escaping @MainActor () -> Void) {
             self.action = action
         }
     }
 
-    public func runInMainThread(action: @escaping () -> Void) {
+    public func runInMainThread(action: @escaping @MainActor () -> Void) {
         let action = ThreadActionContext(action: action)
         g_idle_add_full(
             0,
@@ -331,9 +331,11 @@ public final class GtkBackend: AppBackend {
                     fatalError("Gtk action callback called without context")
                 }
 
-                let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
-                    .takeUnretainedValue()
-                action.action()
+                MainActor.assumeIsolated {
+                    let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
+                        .takeUnretainedValue()
+                    action.action()
+                }
 
                 return 0
             },
@@ -355,9 +357,11 @@ public final class GtkBackend: AppBackend {
                     fatalError("Gtk action callback called without context")
                 }
 
-                let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
-                    .takeUnretainedValue()
-                action.action()
+                MainActor.assumeIsolated {
+                    let action = Unmanaged<ThreadActionContext>.fromOpaque(context)
+                        .takeUnretainedValue()
+                    action.action()
+                }
 
                 // Cancel the recurring timeout after one iteration
                 return 0

Sources/GtkBackend/GtkBackend.swift

@@ -104,7 +104,7 @@ extension HotReloadableAppMacro: MemberMacro {
 
                     if !hotReloadingHasConnectedToServer {
                         hotReloadingHasConnectedToServer = true
-                        Task {
+                        Task { @MainActor
                             do {
                                 var client = try await HotReloadingClient()
                                 print("Hot reloading: received new dylib")

Sources/HotReloadingMacrosPlugin/HotReloadableAppMacro.swift

@@ -1,6 +1,7 @@
 import Foundation
 
 /// An application.
+@MainActor
 public protocol App {
     /// The backend used to render the app.
     associatedtype Backend: AppBackend
@@ -24,14 +25,16 @@ public protocol App {
 
 /// Force refresh the entire scene graph. Used by hot reloading. If you need to do
 /// this in your own code then something has gone very wrong...
+@MainActor
 public var _forceRefresh: () -> Void = {}
 
 /// Metadata embedded by Swift Bundler if present. Loaded at app start up.
+@MainActor
 private var swiftBundlerAppMetadata: AppMetadata?
 
 /// An error encountered when parsing Swift Bundler metadata.
 private enum SwiftBundlerMetadataError: LocalizedError {
-    case jsonNotDictionary(Any)
+    case jsonNotDictionary(String)
     case missingAppIdentifier
     case missingAppVersion
 
@@ -94,7 +97,7 @@ extension App {
             // require a lot of boilerplate code to parse with Codable).
             let jsonValue = try JSONSerialization.jsonObject(with: jsonData)
             guard let json = jsonValue as? [String: Any] else {
-                throw SwiftBundlerMetadataError.jsonNotDictionary(jsonValue)
+                throw SwiftBundlerMetadataError.jsonNotDictionary(String(describing: jsonValue))
             }
             guard let identifier = json["appIdentifier"] as? String else {
                 throw SwiftBundlerMetadataError.missingAppIdentifier

Sources/SwiftCrossUI/App.swift

@@ -40,7 +40,8 @@ import Foundation
 /// code between the `create` and `update` methods of the various widgets
 /// (since the `update` method is always called between calling `create`
 /// and actually displaying the widget anyway).
-public protocol AppBackend {
+@MainActor
+public protocol AppBackend: Sendable {
     associatedtype Window
     associatedtype Widget
     associatedtype Menu
@@ -120,7 +121,7 @@ public protocol AppBackend {
     /// setup function is passed to `Gtk` as a callback to run once the main
     /// run loop starts.
     func runMainLoop(
-        _ callback: @escaping () -> Void
+        _ callback: @escaping @MainActor () -> Void
     )
     /// Creates a new window. For some backends it may make sense for this
     /// method to return the application's root window the first time its
@@ -174,7 +175,7 @@ public protocol AppBackend {
     /// Runs an action in the app's main thread if required to perform UI updates
     /// by the backend. Predominantly used by ``Publisher`` to publish changes to a thread
     /// compatible with dispatching UI updates. Can be synchronous or asynchronous (for now).
-    func runInMainThread(action: @escaping () -> Void)
+    nonisolated func runInMainThread(action: @escaping @MainActor () -> Void)
 
     /// Computes the root environment for an app (e.g. by checking the system's current
     /// theme). May fall back on the provided defaults where reasonable.
@@ -193,7 +194,7 @@ public protocol AppBackend {
     /// A default implementation is provided. It uses the backend's reported
     /// device class and looks up the text style in a lookup table derived
     /// from Apple's typography guidelines. See ``TextStyle/resolve(for:)``.
-    @Sendable func resolveTextStyle(_ textStyle: Font.TextStyle) -> Font.TextStyle.Resolved
+    func resolveTextStyle(_ textStyle: Font.TextStyle) -> Font.TextStyle.Resolved
 
     /// Computes a window's environment based off the root environment. This may involve
     /// updating ``EnvironmentValues/windowScaleFactor`` etc.
@@ -683,7 +684,6 @@ public protocol AppBackend {
 }
 
 extension AppBackend {
-    @Sendable
     public func resolveTextStyle(
         _ textStyle: Font.TextStyle
     ) -> Font.TextStyle.Resolved {

Sources/SwiftCrossUI/Backend/AppBackend.swift

@@ -16,7 +16,7 @@ public struct ResolvedMenu {
     /// A menu item.
     public enum Item {
         /// A button. A `nil` action means that the button is disabled.
-        case button(_ label: String, _ action: (() -> Void)?)
+        case button(_ label: String, _ action: (@MainActor () -> Void)?)
         /// A named submenu.
         case submenu(Submenu)
     }

Sources/SwiftCrossUI/Backend/ResolvedMenu.swift

@@ -4,9 +4,9 @@
 /// This exists to avoid having to expose internal details of ``Button``, since
 /// breaking ``Button``'s API would have much more wide-reaching impacts than
 /// breaking this single-purpose API.
-public struct AlertAction {
+public struct AlertAction: Sendable {
     public static let ok = AlertAction(label: "Ok", action: {})
 
     public var label: String
-    public var action: () -> Void
+    public var action: @MainActor @Sendable () -> Void
 }

Sources/SwiftCrossUI/Environment/Actions/AlertAction.swift

@@ -2,6 +2,7 @@ import Foundation
 
 /// Opens a URL with the default application. May present an application picker
 /// if multiple applications are registered for the given URL protocol.
+@MainActor
 public struct OpenURLAction {
     let action: (URL) -> Void
 

Sources/SwiftCrossUI/Environment/Actions/OpenURLAction.swift

@@ -3,6 +3,7 @@
 /// selected action. By default, the alert will have a single button labelled
 /// `OK`. All buttons will dismiss the alert even if you provide your own
 /// actions.
+@MainActor
 public struct PresentAlertAction {
     let environment: EnvironmentValues
 

Sources/SwiftCrossUI/Environment/Actions/PresentAlertAction.swift

@@ -2,9 +2,9 @@ import Foundation
 
 /// Presents a 'Save file' dialog fit for selecting a save destination. Returns
 /// `nil` if the user cancels the operation.
-public struct PresentFileSaveDialogAction {
+public struct PresentFileSaveDialogAction: Sendable {
     let backend: any AppBackend
-    let window: Any?
+    let window: MainActorBox<Any?>
 
     public func callAsFunction(
         title: String = "Save",
@@ -19,7 +19,7 @@ public struct PresentFileSaveDialogAction {
             return await withCheckedContinuation { continuation in
                 backend.runInMainThread {
                     let window: Backend.Window? =
-                        if let window = self.window {
+                        if let window = self.window.value {
                             .some(window as! Backend.Window)
                         } else {
                             nil

Sources/SwiftCrossUI/Environment/Actions/PresentFileSaveDialogAction.swift

@@ -3,9 +3,9 @@ import Foundation
 /// Presents an 'Open file' dialog fit for selecting a single file. Some
 /// backends only allow selecting either files or directories but not both
 /// in a single dialog. Returns `nil` if the user cancels the operation.
-public struct PresentSingleFileOpenDialogAction {
+public struct PresentSingleFileOpenDialogAction: Sendable {
     let backend: any AppBackend
-    let window: Any?
+    let window: MainActorBox<Any?>
 
     public func callAsFunction(
         title: String = "Open",
@@ -20,7 +20,7 @@ public struct PresentSingleFileOpenDialogAction {
             await withCheckedContinuation { continuation in
                 backend.runInMainThread {
                     let window: Backend.Window? =
-                        if let window = self.window {
+                        if let window = self.window.value {
                             .some(window as! Backend.Window)
                         } else {
                             nil

Sources/SwiftCrossUI/Environment/Actions/PresentSingleFileOpenDialogAction.swift

@@ -2,6 +2,7 @@ import Foundation
 
 /// Reveals a file in the system's file manager. This opens
 /// the file's enclosing directory and highlighting the file.
+@MainActor
 public struct RevealFileAction {
     let action: (URL) -> Void