feat: Add discovery of dev-server add-ins

src/Uno.Sdk/targets/Uno.Build.targets

@@ -141,6 +141,14 @@
 
 	</Target>
 
+	<Target Name="UnoDumpTargetFrameworks">
+		<!--
+			This target is used to dump the target frameworks to the output window.
+			It is useful to determine all target frameworks used by all projects of a solution.
+		-->
+		<Message Text="&lt;TargetFrameworks&gt;$(TargetFramework);$(TargetFrameworks)&lt;/TargetFrameworks&gt;" Importance="High" />
+	</Target>
+
 	<Import Project="Uno.SingleProject.VS.Build.targets"
 			Condition=" '$(UnoSingleProject)' == 'true' AND '$(BuildingInsideVisualStudio)' == 'true' " />
 </Project>

src/Uno.UI.RemoteControl.Host/Extensibility/AddIns.cs

@@ -1,26 +1,75 @@
 using System;
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
 using System.Text.RegularExpressions;
+using Microsoft.Extensions.Logging;
+using Uno.Extensions;
 using Uno.UI.RemoteControl.Helpers;
 
 namespace Uno.UI.RemoteControl.Host.Extensibility;
 
 public class AddIns
 {
+	private static ILogger _log = typeof(AddIns).Log();
+
 	public static IImmutableList<string> Discover(string solutionFile)
-		=> ProcessHelper.RunProcess("dotnet", $"build \"{solutionFile}\" /t:GetRemoteControlAddIns /nowarn:MSB4057") switch // Ignore missing target
+	{
+		// Note: With .net 9 we need to specify --verbosity detailed to get messages with High importance.
+		var result = ProcessHelper.RunProcess("dotnet", $"build \"{solutionFile}\" --target:UnoDumpTargetFrameworks --verbosity detailed");
+		var targetFrameworks = GetConfigurationValue(result.output ?? "", "TargetFrameworks")
+			.SelectMany(tfms => tfms.Split(['\r', '\n', ';', ','], StringSplitOptions.RemoveEmptyEntries))
+			.Select(tfm => tfm.Trim())
+			.Distinct(StringComparer.OrdinalIgnoreCase)
+			.ToImmutableList();
+
+		if (targetFrameworks.IsEmpty)
+		{
+			if (_log.IsEnabled(LogLevel.Warning))
+			{
+				_log.Log(LogLevel.Warning, new Exception(result.error), $"Failed to get target frameworks of solution '{solutionFile}' (cf. inner exception for details).");
+			}
+
+			return new ImmutableArray<string>();
+		}
+
+
+		foreach (var targetFramework in targetFrameworks)
 		{
-			// Note: We ignore the exitCode not being 0: even if flagged as nowarn, we can still get MSB4057 for project that does not have the target GetRemoteControlAddIns
-			{ error: { Length: > 0 } err } => throw new InvalidOperationException($"Failed to get add-ins for solution '{solutionFile}' (cf. inner exception for details).", new Exception(err)),
-			var result => GetConfigurationValue(result.output, "RemoteControlAddIns")
-				?.Split(['\r', '\n', ';', ','], StringSplitOptions.RemoveEmptyEntries)
+			result = ProcessHelper.RunProcess("dotnet", $"build \"{solutionFile}\" --target:UnoDumpRemoteControlAddIns --verbosity detailed --framework \"{targetFramework}\" -nowarn:MSB4057");
+			if (!string.IsNullOrWhiteSpace(result.error))
+			{
+				if (_log.IsEnabled(LogLevel.Warning))
+				{
+					_log.Log(LogLevel.Warning, new Exception(result.error), $"Failed to get add-ins for solution '{solutionFile}' for tfm {targetFramework} (cf. inner exception for details).");
+				}
+
+				continue;
+			}
+
+			var addIns = GetConfigurationValue(result.output, "RemoteControlAddIns")
+				.SelectMany(tfms => tfms.Split(['\r', '\n', ';', ','], StringSplitOptions.RemoveEmptyEntries))
+				.Select(tfm => tfm.Trim())
 				.Distinct(StringComparer.OrdinalIgnoreCase)
-				.ToImmutableList() ?? ImmutableList<string>.Empty,
-		};
+				.ToImmutableList();
+
+			if (!addIns.IsEmpty)
+			{
+				return addIns;
+			}
+		}
+
+		if (_log.IsEnabled(LogLevel.Information))
+		{
+			_log.Log(LogLevel.Information, $"Didn't find any add-ins for solution '{solutionFile}'.");
+		}
+
+		return ImmutableList<string>.Empty;
+	}
 
-	private static string? GetConfigurationValue(string msbuildResult, string nodeName)
-		=> Regex.Match(msbuildResult, $"<{nodeName}>(?<value>.*)</{nodeName}>") is { Success: true } match
-			? match.Groups["value"].Value
-			: null;
+	private static IEnumerable<string> GetConfigurationValue(string msbuildResult, string nodeName)
+		=> Regex
+			.Matches(msbuildResult, $"<{nodeName}>(?<value>.*)</{nodeName}>")
+			.Where(match => match.Success)
+			.Select(match => match.Groups["value"].Value);
 }

src/Uno.UI.RemoteControl.Host/Extensibility/Uno.Extensions.DependencyInjection/AttributeDataExtensions.cs

@@ -11,7 +11,7 @@ internal static class AttributeDataExtensions
 
 	public static object? TryCreate(this CustomAttributeData data, Type attribute)
 	{
-		if (!data.AttributeType.FullName?.Equals(attribute.FullName, StringComparison.Ordinal) ?? false)
+		if ((!data.AttributeType.FullName?.Equals(attribute.FullName, StringComparison.Ordinal)) ?? true)
 		{
 			return null;
 		}
@@ -45,12 +45,12 @@ internal static class AttributeDataExtensions
 				instance = ctor.Invoke(args);
 				break;
 			}
-			catch { }
+			catch { /* Nothing to do, lets try another constructor */ }
 		}
 
 		if (instance is null)
 		{
-			return null;
+			return null; // Failed to find a valid constructor.
 		}
 
 		try

src/Uno.UI.RemoteControl.Host/Extensibility/Uno.Extensions.DependencyInjection/ServiceAttribute.cs

@@ -4,19 +4,40 @@
 
 namespace Uno.Extensions.DependencyInjection;
 
+/// <summary>
+/// Attribute to define a service registration in the service collection.
+/// </summary>
+/// <param name="contract">Type of the contract (i.e. interface) implemented by the concrete <see cref="Implementation"/> type.</param>
+/// <param name="implementation">Concrete type to register in the service collection.</param>
 [AttributeUsage(AttributeTargets.Assembly)]
 public class ServiceAttribute(Type contract, Type implementation) : Attribute
 {
+	/// <summary>
+	/// Creates a new instance of the <see cref="ServiceAttribute"/> class with only a concrete type (used as contract and implementation).
+	/// </summary>
+	/// <param name="implementation">Concrete type to register in the service collection.</param>
 	public ServiceAttribute(Type implementation)
 		: this(implementation, implementation)
 	{
 	}
 
+	/// <summary>
+	/// Type of the contract (i.e. interface) implemented by the concrete <see cref="Implementation"/> type.
+	/// </summary>
 	public Type Contract { get; } = contract;
 
+	/// <summary>
+	/// Concrete type to register in the service collection.
+	/// </summary>
 	public Type Implementation { get; } = implementation;
 
+	/// <summary>
+	/// The lifetime of the service.
+	/// </summary>
 	public ServiceLifetime LifeTime { get; set; } = ServiceLifetime.Singleton;
 
+	/// <summary>
+	/// Indicates if the service should be automatically initialized at startup.
+	/// </summary>
 	public bool IsAutoInit { get; set; }
 }

src/Uno.UI.RemoteControl.Host/Extensibility/Uno.Extensions.DependencyInjection/ServiceCollectionServiceExtensions.cs

@@ -6,12 +6,16 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
-using Uno.UI.RemoteControl.Host.Extensibility;
 
 namespace Uno.Extensions.DependencyInjection;
 
 public static class ServiceCollectionServiceExtensions
 {
+	/// <summary>
+	/// Register services configured with the <see cref="ServiceAttribute"/> attribute from all loaded assemblies.
+	/// </summary>
+	/// <param name="svc">The service collection on which services should be registered.</param>
+	/// <returns>The service collection for fluent usage.</returns>
 	public static IServiceCollection AddFromAttribute(this IServiceCollection svc)
 	{
 		var attribute = typeof(ServiceAttribute);
@@ -45,14 +49,14 @@ protected override Task ExecuteAsync(CancellationToken stoppingToken)
 
 					if (this.Log().IsEnabled(LogLevel.Information))
 					{
-						this.Log().Log(LogLevel.Information, $"Successfully created an instance of {attr.Contract} (impl: {svc?.GetType()})");
+						this.Log().Log(LogLevel.Information, $"Successfully created an instance of {attr.Contract} for auto-init (impl: {svc?.GetType()})");
 					}
 				}
 				catch (Exception error)
 				{
 					if (this.Log().IsEnabled(LogLevel.Error))
 					{
-						this.Log().Log(LogLevel.Error, error, $"Failed to create an instance of {attr.Contract}.");
+						this.Log().Log(LogLevel.Error, error, $"Failed to create an instance of {attr.Contract} for auto-init.");
 					}
 				}
 			}

src/Uno.UI.RemoteControl.Host/Uno.UI.RemoteControl.Host.csproj

@@ -31,6 +31,7 @@
 
 	<ItemGroup>
 		<Compile Include="..\Uno.UI.RemoteControl\Helpers\**\*.cs" Link="Helpers/%(Filename)" />
+		<Compile Include="..\Uno.UI.RemoteControl.Server.Processors\Helpers\**\*.cs" Link="Helpers/%(Filename)" />
 	</ItemGroup>
 
 	<ItemGroup>

src/Uno.UI.RemoteControl.VS/EntryPoint.cs

@@ -16,6 +16,7 @@
 using Microsoft.Build.Evaluation;
 using Microsoft.Internal.VisualStudio.Shell;
 using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Threading;
 using Microsoft.VisualStudio.Shell.Interop;
 using Uno.UI.RemoteControl.Messaging.IdeChannel;
 using Uno.UI.RemoteControl.VS.DebuggerHelper;
@@ -348,17 +349,20 @@ private async Task EnsureServerAsync()
 				// Set the port to the projects
 				// This LEGACY as port should be set through the global properties (cf. OnProvideGlobalPropertiesAsync)
 				var portString = _remoteControlServerPort.ToString(CultureInfo.InvariantCulture);
-				foreach (var p in await _dte.GetProjectsAsync())
+				await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
+				var projects = (await _dte.GetProjectsAsync()).ToArray(); // EnumerateProjects must be called on the UI thread.
+				await TaskScheduler.Default;
+				foreach (var project in projects)
 				{
 					var filename = string.Empty;
 					try
 					{
-						filename = p.FileName;
+						filename = project.FileName;
 					}
 					catch (Exception ex)
 					{
-						_debugAction?.Invoke($"Exception on retrieving {p.UniqueName} details. Err: {ex}.");
-						_warningAction?.Invoke($"Cannot read {p.UniqueName} project details (It may be unloaded).");
+						_debugAction?.Invoke($"Exception on retrieving {project.UniqueName} details. Err: {ex}.");
+						_warningAction?.Invoke($"Cannot read {project.UniqueName} project details (It may be unloaded).");
 					}
 					if (string.IsNullOrWhiteSpace(filename) == false
 						&& GetMsbuildProject(filename) is Microsoft.Build.Evaluation.Project msbProject
@@ -478,7 +482,7 @@ public void SetGlobalProperty(string projectFullName, string propertyName, strin
 		}
 	}
 
-	private static Microsoft.Build.Evaluation.Project GetMsbuildProject(string projectFullName)
+	private static Microsoft.Build.Evaluation.Project? GetMsbuildProject(string projectFullName)
 		=> ProjectCollection.GlobalProjectCollection.GetLoadedProjects(projectFullName).FirstOrDefault();
 
 	public void SetGlobalProperties(string projectFullName, IDictionary<string, string> properties)

src/Uno.UI.RemoteControl/buildTransitive/Uno.WinUI.DevServer.targets

@@ -31,6 +31,10 @@
 		<Message Text="&lt;IsRCClientRemote&gt;$(_IsRCClientRemote)&lt;/IsRCClientRemote&gt;" Importance="High" />
 	</Target>
 
+	<Target Name="GetRemoteControlAddIns">
+		<Message Text="&lt;RemoteControlAddIns&gt;@(UnoRemoteControlAddIns)&lt;/RemoteControlAddIns&gt;" Importance="High" />
+	</Target>
+
 	<!-- .NET 7 and earlier compatibility for .NET8 msbuild CLI `getProperty` equivalent -->
 	<Target Name="UnoVSCodeGetProjectProperties">
 		<Message Text='{%0a  "Properties": {%0a    "TargetFramework": "$(TargetFramework)",' Importance="High" />