Implement the ITypeDiscoveryService service

src/System.Windows.Forms/tests/IntegrationTests/DesignSurface/DesignSurfaceExt/DesignSurfaceExt.cs

@@ -309,15 +309,11 @@ private void InitServices()
         //- We can leave the default services in their present state,
         //- or we can remove them and replace them with our own.
         //- Now add our own services using IServiceContainer
-        //-
-        //-
         //- Note
         //- before loading the root control in the design surface
         //- we must add an instance of naming service to the service container.
         //- otherwise the root component did not have a name and this caused
         //- troubles when we try to use the UndoEngine
-        //-
-        //-
         //- 1. NameCreationService
         _nameCreationService = new NameCreationServiceImp();
         if (_nameCreationService is not null)
@@ -326,8 +322,6 @@ private void InitServices()
             ServiceContainer.AddService(typeof(INameCreationService), _nameCreationService);
         }
 
-        //-
-        //-
         //- 2. CodeDomComponentSerializationService
         _codeDomComponentSerializationService = new CodeDomComponentSerializationService(ServiceContainer);
         if (_codeDomComponentSerializationService is not null)
@@ -337,8 +331,6 @@ private void InitServices()
             ServiceContainer.AddService(typeof(ComponentSerializationService), _codeDomComponentSerializationService);
         }
 
-        //-
-        //-
         //- 3. IDesignerSerializationService
         _designerSerializationService = new DesignerSerializationServiceImpl(ServiceContainer);
         if (_designerSerializationService is not null)
@@ -348,8 +340,6 @@ private void InitServices()
             ServiceContainer.AddService(typeof(IDesignerSerializationService), _designerSerializationService);
         }
 
-        //-
-        //-
         //- 4. UndoEngine
         _undoEngine = new UndoEngineExt(ServiceContainer);
         //- disable the UndoEngine
@@ -361,10 +351,11 @@ private void InitServices()
             ServiceContainer.AddService(typeof(UndoEngine), _undoEngine);
         }
 
-        //-
-        //-
         //- 5. IMenuCommandService
         ServiceContainer.AddService(typeof(IMenuCommandService), new MenuCommandService(this));
+
+        //- 6. ITypeDiscoveryService
+        ServiceContainer.AddService(typeof(ITypeDiscoveryService), new TypeDiscoveryService());
     }
 
     //- do some Edit menu command using the MenuCommandService

src/System.Windows.Forms/tests/IntegrationTests/DesignSurface/DesignSurfaceExt/TypeDiscoveryService.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using System.Collections.Concurrent;
+using System.Collections.Immutable;
+using System.Reflection;
+
+namespace System.ComponentModel.Design;
+
+/// <summary>
+///  This service is requested by <see cref="TypeDescriptor" /> when asking for type information for a component.
+///  This is a sample implementation suitable for this sample application.
+/// </summary>
+internal class TypeDiscoveryService : ITypeDiscoveryService
+{
+    public TypeDiscoveryService() { }
+
+    private readonly ConcurrentDictionary<Type, ImmutableArray<Type>> _discoveredTypesCache = new();
+
+    public ICollection GetTypes(Type baseType, bool excludeGlobalTypes)
+    {
+        return baseType is null
+            ? throw new ArgumentNullException(nameof(baseType))
+            : (ICollection)_discoveredTypesCache.GetOrAdd(baseType, type => FindTypes(type, AppDomain.CurrentDomain.GetAssemblies()));
+
+        static ImmutableArray<Type> FindTypes(Type baseType, Assembly[] assemblies)
+        {
+            var builder = ImmutableArray.CreateBuilder<Type>();
+
+            foreach (var assembly in assemblies)
+            {
+                Type[] types;
+                try
+                {
+                    types = assembly.GetTypes();
+                }
+                catch (ReflectionTypeLoadException exception)
+                {
+                    types = exception.Types!;
+                }
+
+                foreach (var type in types)
+                {
+                    if (baseType.IsAssignableFrom(type))
+                    {
+                        builder.Add(type);
+                    }
+                }
+            }
+
+            return builder.ToImmutable();
+        }
+    }
+}