Merge pull request #19328 from unoplatform/mergify/bp/release/stable/…

…5.6/pr-19326

fix: Ensure the assembly loader is registered early (backport #19326)

src/Uno.UI.RemoteControl.Server.Processors/HotReload/MetadataUpdates/CompilationWorkspaceProvider.cs

@@ -167,7 +167,7 @@ private static string BuildMSBuildPath(string? workDir)
 			throw new InvalidOperationException("Unable to find dotnet SDK base path");
 		}
 
-		private static void RegisterAssemblyLoader()
+		public static void RegisterAssemblyLoader()
 		{
 			// Force assembly loader to consider siblings, when running in a separate appdomain / ALC.
 			Assembly? Load(string name)

src/Uno.UI.RemoteControl.Server.Processors/HotReload/ServerHotReloadProcessor.MetadataUpdate.cs

@@ -7,6 +7,7 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
@@ -42,7 +43,10 @@ private bool InitializeMetadataUpdater(ConfigureServer configureServer)
 
 			if (_useRoslynHotReload)
 			{
-				CompilationWorkspaceProvider.InitializeRoslyn(Path.GetDirectoryName(configureServer.ProjectPath));
+				// Assembly registrations must be done before the workspace is initialized
+				// Not doing so will cause the roslyn msbuild workspace to fail to load because
+				// of a missing path on assemblies loaded from a memory stream.
+				CompilationWorkspaceProvider.RegisterAssemblyLoader();
 
 				InitializeInner(configureServer);
 
@@ -54,7 +58,22 @@ private bool InitializeMetadataUpdater(ConfigureServer configureServer)
 			}
 		}
 
-		private void InitializeInner(ConfigureServer configureServer) => _initializeTask = Task.Run(
+		private void InitializeInner(ConfigureServer configureServer)
+		{
+			if (Assembly.Load("Microsoft.CodeAnalysis.Workspaces") is { } wsAsm)
+			{
+				// If this assembly was loaded from a stream, it will not have a location.
+				// This will indicate that the assembly loader from CompilationWorkspaceProvider
+				// has been registered too late.
+				if (string.IsNullOrEmpty(wsAsm.Location))
+				{
+					throw new InvalidOperationException("Microsoft.CodeAnalysis.Workspaces was loaded from a stream and must loaded from a known path");
+				}
+			}
+
+			CompilationWorkspaceProvider.InitializeRoslyn(Path.GetDirectoryName(configureServer.ProjectPath));
+
+			_initializeTask = Task.Run(
 			async () =>
 			{
 				try
@@ -103,6 +122,7 @@ private void InitializeInner(ConfigureServer configureServer) => _initializeTask
 				}
 			},
 			CancellationToken.None);
+		}
 
 		private void ObserveSolutionPaths(Solution solution)
 		{