Add @mainactor and Sendable annotations

Author: bbrk24

Sources/SwiftCrossUI/App.swift

@@ -1,6 +1,7 @@
 import Foundation
 
 /// An application.
+@MainActor
 public protocol App {
     /// The backend used to render the app.
     associatedtype Backend: AppBackend

Sources/SwiftCrossUI/Backend/AppBackend.swift

@@ -40,6 +40,7 @@ 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).
+@MainActor
 public protocol AppBackend {
     associatedtype Window
     associatedtype Widget
@@ -118,7 +119,7 @@ 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
@@ -172,7 +173,7 @@ 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.

Sources/SwiftCrossUI/Backend/ResolvedMenu.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/Environment/Actions/OpenURLAction.swift

@@ -3,7 +3,7 @@ import Foundation
 /// Opens a URL with the default application. May present an application picker
 /// if multiple applications are registered for the given URL protocol.
 public struct OpenURLAction {
-    let action: (URL) -> Void
+    let action: @MainActor (URL) -> Void
 
     init<Backend: AppBackend>(backend: Backend) {
         action = { url in
@@ -15,6 +15,7 @@ public struct OpenURLAction {
         }
     }
 
+    @MainActor
     public func callAsFunction(_ url: URL) {
         action(url)
     }

Sources/SwiftCrossUI/Environment/Actions/RevealFileAction.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
 

Sources/SwiftCrossUI/Environment/EnvironmentValues.swift

@@ -33,7 +33,7 @@ public struct EnvironmentValues {
 
     /// Called when a text field gets submitted (usually due to the user
     /// pressing Enter/Return).
-    public var onSubmit: (() -> Void)?
+    public var onSubmit: (@MainActor () -> Void)?
 
     /// The scale factor of the current window.
     public var windowScaleFactor: Double
@@ -55,7 +55,7 @@ public struct EnvironmentValues {
     /// change and end up changing size. Each view graph node sets its own
     /// handler when passing the environment on to its children, setting up
     /// a bottom-up update chain up which resize events can propagate.
-    var onResize: (_ newSize: ViewSize) -> Void
+    var onResize: @MainActor (_ newSize: ViewSize) -> Void
 
     /// The style of list to use.
     package var listStyle: ListStyle
@@ -74,6 +74,7 @@ public struct EnvironmentValues {
 
     /// Brings the current window forward, not guaranteed to always bring
     /// the window to the top (due to focus stealing prevention).
+    @MainActor
     func bringWindowForward() {
         func activate<Backend: AppBackend>(with backend: Backend) {
             backend.activate(window: window as! Backend.Window)
@@ -140,6 +141,7 @@ public struct EnvironmentValues {
     ///
     /// `nil` on platforms that don't support revealing files, e.g.
     /// iOS.
+    @MainActor
     public var revealFile: RevealFileAction? {
         return RevealFileAction(
             backend: backend

Sources/SwiftCrossUI/Layout/LayoutSystem.swift

@@ -75,6 +75,7 @@ public enum LayoutSystem {
     ///   if all of its children have it set to true. This allows views such as
     ///   ``Group`` to avoid changing stack layout participation (since ``Group``
     ///   is meant to appear completely invisible to the layout system).
+    @MainActor
     public static func updateStackLayout<Backend: AppBackend>(
         container: Backend.Widget,
         children: [LayoutableChild],

Sources/SwiftCrossUI/Scenes/SceneGraphNode.swift

@@ -3,6 +3,7 @@
 ///
 /// Treat scenes as basic data structures that simply encode the structure of the app;
 /// the actual rendering and logic is handled by the node.
+@MainActor
 public protocol SceneGraphNode: AnyObject {
     /// The type of scene managed by this node.
     associatedtype NodeScene: Scene where NodeScene.Node == Self

Sources/SwiftCrossUI/Values/Alignment.swift

@@ -1,5 +1,5 @@
 /// The 2d alignment of a view.
-public struct Alignment: Hashable {
+public struct Alignment: Hashable, Sendable {
     /// Centered in both dimensions.
     public static let center = Self(horizontal: .center, vertical: .center)
 

Sources/SwiftCrossUI/Values/Axis.swift

@@ -1,5 +1,5 @@
 /// An axis in a 2D coordinate system.
-public enum Axis {
+public enum Axis: Sendable {
     /// The horizontal axis.
     case horizontal
     /// The vertical axis.