Simplify and unify assembly loader provider

src/Workspaces/Core/Portable/Workspace/Host/Metadata/IAnalyzerAssemblyLoaderProvider.cs

@@ -2,9 +2,49 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Composition;
+using System.IO;
+using Microsoft.CodeAnalysis.Host.Mef;
+
 namespace Microsoft.CodeAnalysis.Host;
 
 internal interface IAnalyzerAssemblyLoaderProvider : IWorkspaceService
 {
     IAnalyzerAssemblyLoaderInternal GetShadowCopyLoader();
 }
+
+/// <summary>
+/// Abstract implementation of an analyzer assembly loader that can be used by VS/VSCode to provide a <see
+/// cref="IAnalyzerAssemblyLoader"/> with an appropriate path.
+/// </summary>
+internal abstract class AbstractAnalyzerAssemblyLoaderProvider : IAnalyzerAssemblyLoaderProvider
+{
+    private readonly Lazy<IAnalyzerAssemblyLoaderInternal> _shadowCopyLoader;
+
+    public AbstractAnalyzerAssemblyLoaderProvider(ImmutableArray<IAnalyzerAssemblyResolver> externalResolvers)
+    {
+        // We use a lazy here in case creating the loader requires MEF imports in the derived constructor.
+        _shadowCopyLoader = new(() => CreateShadowCopyLoader(externalResolvers));
+    }
+
+    public IAnalyzerAssemblyLoaderInternal GetShadowCopyLoader()
+        => _shadowCopyLoader.Value;
+
+    protected virtual IAnalyzerAssemblyLoaderInternal CreateShadowCopyLoader(ImmutableArray<IAnalyzerAssemblyResolver> externalResolvers)
+        => DefaultAnalyzerAssemblyLoader.CreateNonLockingLoader(
+            GetDefaultShadowCopyPath(),
+            externalResolvers: externalResolvers);
+
+    public static string GetDefaultShadowCopyPath()
+        => Path.Combine(Path.GetTempPath(), "Roslyn", "AnalyzerAssemblyLoader");
+}
+
+[ExportWorkspaceService(typeof(IAnalyzerAssemblyLoaderProvider)), Shared]
+[method: ImportingConstructor]
+[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
+internal sealed class DefaultAnalyzerAssemblyLoaderService(
+    [ImportMany] IEnumerable<IAnalyzerAssemblyResolver> externalResolvers)
+    : AbstractAnalyzerAssemblyLoaderProvider(externalResolvers.ToImmutableArray());