feat: Add diagnostics indicator for hot-reload

src/Uno.CrossTargetting.targets

@@ -137,7 +137,7 @@
 			<_OverrideTargetFramework Condition="$(_OverrideTargetFramework.EndsWith('.0-android'))">$(_OverrideTargetFramework)30.0</_OverrideTargetFramework>
 
 			<_overridePackageId>$(CommonOverridePackageId.ToLowerInvariant())</_overridePackageId>
-			<_overridePackageId Condition="'$(CommonOverridePackageId)'==''">$(AssemblyName.ToLowerVariant())</_overridePackageId>
+			<_overridePackageId Condition="'$(CommonOverridePackageId)'==''">$(AssemblyName.ToLowerInvariant())</_overridePackageId>
 			<_overridePackageId Condition="'$(UNO_UWP_BUILD)'=='false'">$(_overridePackageId.Replace('uno.ui','uno.winui'))</_overridePackageId>
 			<_TargetNugetFolder>$(NuGetPackageRoot)\$(_overridePackageId)\$(UnoNugetOverrideVersion)\lib\$(_OverrideTargetFramework)</_TargetNugetFolder>
 			<_TargetNugetRefFolder>$(NuGetPackageRoot)\$(_overridePackageId)\$(UnoNugetOverrideVersion)\ref\$(_OverrideTargetFramework)</_TargetNugetRefFolder>

src/Uno.Foundation/Diagnostics/DiagnosticViewNotification.cs

@@ -0,0 +1,29 @@
+#nullable enable
+using System;
+using System.ComponentModel;
+using System.Linq;
+
+namespace Uno.Diagnostics.UI;
+
+/// <summary>
+/// A notification sent by a diagnostic view to visually show an important status.
+/// </summary>
+/// <param name="content">The content of the notification.</param>
+/// <param name="duration">Configures the duration to wait before automatically hide the notification.</param>
+public class DiagnosticViewNotification(object content, TimeSpan? duration = null)
+{
+	[EditorBrowsable(EditorBrowsableState.Never)] // For XAML only
+	public DiagnosticViewNotification() : this(default!)
+	{
+	}
+
+	/// <summary>
+	/// The content of the notification.
+	/// </summary>
+	public object Content { get; set; } = content;
+
+	/// <summary>
+	/// Configures the duration to wait before automatically hide the notification.
+	/// </summary>
+	public TimeSpan? Duration { get; set; } = duration;
+}

src/Uno.Foundation/Diagnostics/DiagnosticViewRegistry.cs

@@ -0,0 +1,56 @@
+#nullable enable
+using System;
+using System.Collections.Immutable;
+using System.Linq;
+
+namespace Uno.Diagnostics.UI;
+
+/// <summary>
+/// Registry for view that can be displayed by the DiagnosticOverlay.
+/// </summary>
+internal static class DiagnosticViewRegistry
+{
+	internal static EventHandler<IImmutableList<DiagnosticViewRegistration>>? Added;
+
+	private static ImmutableArray<DiagnosticViewRegistration> _registrations = ImmutableArray<DiagnosticViewRegistration>.Empty;
+
+	/// <summary>
+	/// Gets the list of registered diagnostic providers.
+	/// </summary>
+	internal static IImmutableList<DiagnosticViewRegistration> Registrations => _registrations;
+
+	/// <summary>
+	/// Register a global diagnostic view that can be displayed on any window.
+	/// </summary>
+	/// <param name="view">A diagnostic view to display.</param>
+	public static void Register(IDiagnosticView view)
+	{
+		ImmutableInterlocked.Update(
+			ref _registrations,
+			static (providers, provider) => providers.Add(provider),
+			new DiagnosticViewRegistration(DiagnosticViewRegistrationMode.One, view));
+
+		Added?.Invoke(null, _registrations);
+	}
+}
+
+internal record DiagnosticViewRegistration(DiagnosticViewRegistrationMode Mode, IDiagnosticView View);
+
+internal enum DiagnosticViewRegistrationMode
+{
+	/// <summary>
+	/// Diagnostic is being rendered as overlay on each window.
+	/// </summary>
+	All,
+
+	/// <summary>
+	/// Diagnostic is being display on at least one window.
+	/// I.e. only the main/first opened but move to the next one if the current window is closed.
+	/// </summary>
+	One,
+
+	/// <summary>
+	/// Only registers the diagnostic provider but does not display it.
+	/// </summary>
+	OnDemand
+}

src/Uno.Foundation/Diagnostics/IDiagnosticView.cs

@@ -0,0 +1,40 @@
+#nullable enable
+using System;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Uno.Diagnostics.UI;
+
+/// <summary>
+/// A diagnostic entry that can be displayed by the DiagnosticsOverlay.
+/// </summary>
+public interface IDiagnosticView
+{
+	/// <summary>
+	/// Identifier of the diagnostic view than can be used to request to show or remove it from a DiagnosticsOverlay.
+	/// </summary>
+	string Id { get; }
+
+	/// <summary>
+	/// Friendly name of the diagnostic.
+	/// </summary>
+	string Name { get; }
+
+	/// <summary>
+	/// Gets a visual element of the diagnostic, usually a value or an icon.
+	/// </summary>
+	/// <param name="context">An update coordinator that can be used to push updates on the preview.</param>
+	/// <returns>Either a UIElement to be displayed by the diagnostic overlay or a plain object (rendered as text).</returns>
+	/// <remarks>This is expected to be invoked on the dispatcher used to render the preview.</remarks>
+	object GetElement(IDiagnosticViewContext context);
+
+	/// <summary>
+	/// Show details of the diagnostic.
+	/// </summary>
+	/// <param name="context">An update coordinator that can be used to push updates on the preview.</param>
+	/// <param name="ct">Token to cancel the async operation.</param>
+	/// <returns>Either a UIElement to be displayed by the diagnostic overlay, a ContentDialog to show, or a simple object to show in a content dialog.</returns>
+	/// <remarks>This is expected to be invoked on the dispatcher used to render the preview.</remarks>
+	ValueTask<object?> GetDetailsAsync(IDiagnosticViewContext context, CancellationToken ct);
+}

src/Uno.Foundation/Diagnostics/IDiagnosticViewContext.cs

@@ -0,0 +1,24 @@
+#nullable enable
+using System;
+using System.Linq;
+
+namespace Uno.Diagnostics.UI;
+
+/// <summary>
+/// Some information on the context where the diagnostic view is being rendered.
+/// </summary>
+/// <remarks>This is mainly an abstraction of the dispatcher that ensure to not overload the UI thread for diagnostics.</remarks>
+public interface IDiagnosticViewContext
+{
+	/// <summary>
+	/// Schedule an update of the diagnostic.
+	/// </summary>
+	/// <param name="action">Update action.</param>
+	void Schedule(Action action);
+
+	void ScheduleRecurrent(Action action);
+
+	void AbortRecurrent(Action action);
+
+	void Notify(DiagnosticViewNotification notification);
+}

src/Uno.UI.RemoteControl.Host/IDEChannel/IdeChannelServer.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 using Uno.UI.RemoteControl.Host.IDEChannel;
 using Uno.UI.RemoteControl.Messaging.IdeChannel;
@@ -22,7 +23,7 @@ public async Task SendToIdeAsync(IdeMessage message)
 		await Task.Yield();
 	}
 
-	public async Task SendToDevServerAsync(IdeMessageEnvelope message)
+	public async Task SendToDevServerAsync(IdeMessageEnvelope message, CancellationToken ct)
 	{
 		MessageFromIDE?.Invoke(this, IdeMessageSerializer.Deserialize(message));