Use GlobalAssemblyCache helper to locate assemblies directly in the GAC

src/Compilers/Shared/GlobalAssemblyCacheHelpers/FusionAssemblyIdentity.cs

@@ -441,7 +441,7 @@ internal static IAssemblyName ToAssemblyNameObject(AssemblyName name)
 
                     throw new ArgumentException(Scripting.ScriptingResources.InvalidCharactersInAssemblyName, nameof(name));
 
-#elif WORKSPACE_DESKTOP
+#elif WORKSPACE_DESKTOP || EDITOR_FEATURES
 
                     throw new ArgumentException(Microsoft.CodeAnalysis.WorkspaceDesktopResources.Invalid_characters_in_assembly_name, nameof(name));
 
@@ -471,7 +471,7 @@ internal static IAssemblyName ToAssemblyNameObject(AssemblyName name)
 
                     throw new ArgumentException(Microsoft.CodeAnalysis.Scripting.ScriptingResources.InvalidCharactersInAssemblyName, nameof(name));
 
-#elif WORKSPACE_DESKTOP
+#elif WORKSPACE_DESKTOP || EDITOR_FEATURES
 
                     throw new ArgumentException(Microsoft.CodeAnalysis.WorkspaceDesktopResources.Invalid_characters_in_assembly_name, nameof(name));
 

src/EditorFeatures/Core/EditorFeatures.csproj

@@ -9,6 +9,7 @@
     <AssemblyName>Microsoft.CodeAnalysis.EditorFeatures</AssemblyName>
     <TargetFramework>net46</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <DefineConstants>$(DefineConstants);EDITOR_FEATURES</DefineConstants>
   </PropertyGroup>
   <ItemGroup Label="Project References">
     <ProjectReference Include="..\..\Compilers\Core\Portable\CodeAnalysis.csproj" />
@@ -94,6 +95,12 @@
     <InternalsVisibleToFSharp Include="FSharp.Editor" />
     <InternalsVisibleToMoq Include="DynamicProxyGenAssembly2" />
   </ItemGroup>
+  <ItemGroup>
+    <Compile Include="..\..\Compilers\Shared\GlobalAssemblyCacheHelpers\ClrGlobalAssemblyCache.cs" Link="Shared\GlobalAssemblyCacheHelpers\ClrGlobalAssemblyCache.cs" />
+    <Compile Include="..\..\Compilers\Shared\GlobalAssemblyCacheHelpers\FusionAssemblyIdentity.cs" Link="Shared\GlobalAssemblyCacheHelpers\FusionAssemblyIdentity.cs" />
+    <Compile Include="..\..\Compilers\Shared\GlobalAssemblyCacheHelpers\GlobalAssemblyCache.cs" Link="Shared\GlobalAssemblyCacheHelpers\GlobalAssemblyCache.cs" />
+    <Compile Include="..\..\Compilers\Shared\GlobalAssemblyCacheHelpers\MonoGlobalAssemblyCache.cs" Link="Shared\GlobalAssemblyCacheHelpers\MonoGlobalAssemblyCache.cs" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Update="EditorFeaturesResources.Designer.cs">
       <DependentUpon>EditorFeaturesResources.resx</DependentUpon>

src/EditorFeatures/Core/Implementation/MetadataAsSource/MetadataAsSourceFileService.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel.Composition;
+using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -200,13 +201,10 @@ private async Task<Document> DecompileSymbolAsync(Document temporaryDocument, IS
             var isReferenceAssembly = symbol.ContainingAssembly.GetAttributes().Any(attribute => attribute.AttributeClass.Name == nameof(ReferenceAssemblyAttribute));
             if (isReferenceAssembly)
             {
-                // Attempt to resolve the assembly via the current process' binding path
                 try
                 {
                     var fullAssemblyName = symbol.ContainingAssembly.Identity.GetDisplayName();
-                    var loadedAssembly = AppDomain.CurrentDomain.GetAssemblies().FirstOrDefault(x => x.FullName == fullAssemblyName);
-                    var assembly = loadedAssembly ?? Assembly.ReflectionOnlyLoad(fullAssemblyName);
-                    assemblyLocation = assembly.Location;
+                    GlobalAssemblyCache.Instance.ResolvePartialName(fullAssemblyName, out assemblyLocation, preferredCulture: CultureInfo.CurrentCulture);
                 }
                 catch (Exception e) when (FatalError.ReportWithoutCrashUnlessCanceled(e))
                 {