Avoid accessing GAC when not available (on CoreCLR)

src/Compilers/Core/Portable/CorLightup.cs

@@ -76,7 +76,7 @@ private static class _Assembly
 
             private static class _ResolveEventArgs
             {
-                internal static readonly Type Type = Type.GetType("System.ResolveEventArgs", throwOnError: false);
+                internal static readonly Type Type = ReflectionUtilities.TryGetType("System.ResolveEventArgs");
 
                 internal static readonly MethodInfo get_Name = Type
                     .GetTypeInfo()
@@ -89,8 +89,8 @@ private static class _ResolveEventArgs
 
             private static class _AppDomain
             {
-                internal static readonly Type Type = Type.GetType("System.AppDomain", throwOnError: false);
-                internal static readonly Type ResolveEventHandlerType = Type.GetType("System.ResolveEventHandler", throwOnError: false);
+                internal static readonly Type Type = ReflectionUtilities.TryGetType("System.AppDomain");
+                internal static readonly Type ResolveEventHandlerType = ReflectionUtilities.TryGetType("System.ResolveEventHandler");
 
                 internal static readonly MethodInfo get_CurrentDomain = Type
                     .GetTypeInfo()

src/Compilers/Core/Portable/InternalUtilities/ReflectionUtilities.cs

@@ -10,17 +10,30 @@ namespace Roslyn.Utilities
 {
     internal static class ReflectionUtilities
     {
+        public static Type TryGetType(string assemblyQualifiedName)
+        {
+            try
+            {
+                // Note that throwOnError=false only suppresses some exceptions, not all.
+                return Type.GetType(assemblyQualifiedName, throwOnError: false);
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
         /// <summary>
         /// Find a <see cref="Type"/> instance by first probing the contract name and then the name as it
         /// would exist in mscorlib.  This helps satisfy both the CoreCLR and Desktop scenarios. 
         /// </summary>
         public static Type GetTypeFromEither(string contractName, string desktopName)
         {
-            var type = Type.GetType(contractName, throwOnError: false);
+            var type = TryGetType(contractName);
 
             if (type == null)
             {
-                type = Type.GetType(desktopName, throwOnError: false);
+                type = TryGetType(desktopName);
             }
 
             return type;

src/Compilers/Helpers/CoreClrShim.cs

@@ -6,7 +6,6 @@
 
 namespace Roslyn.Utilities
 {
-
     /// <summary>
     /// This is a bridge for APIs that are only available on CoreCLR or .NET 4.6
     /// and NOT on .NET 4.5. The compiler currently targets .NET 4.5 and CoreCLR
@@ -14,13 +13,20 @@ namespace Roslyn.Utilities
     /// </summary>
     internal static class CoreClrShim
     {
+        
+        internal static class AssemblyLoadContext
+        {
+            internal static readonly Type Type = ReflectionUtilities.TryGetType(
+               "System.Runtime.Loader.AssemblyLoadContext, System.Runtime.Loader, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a");
+        }
+        
         internal static class CodePagesEncodingProvider
         {
-            internal static readonly Type Type =
-                Type.GetType("System.Text.CodePagesEncodingProvider, " +
-                             "System.Text.Encoding.CodePages, " +
-                             "Version=4.0.0.0, Culture=neutral, " +
-                             "PublicKeyToken=b03f5f7f11d50a3a", throwOnError: false);
+            internal static readonly Type Type = ReflectionUtilities.TryGetType(
+                "System.Text.CodePagesEncodingProvider, " +
+                "System.Text.Encoding.CodePages, " +
+                "Version=4.0.0.0, Culture=neutral, " +
+                "PublicKeyToken=b03f5f7f11d50a3a");
 
             private static PropertyInfo s_instance = Type
                 ?.GetTypeInfo()

src/Compilers/Helpers/GlobalAssemblyCacheHelpers/GacFileResolver.cs

@@ -11,37 +11,46 @@
 namespace Microsoft.CodeAnalysis.Scripting.Hosting
 {
     /// <summary>
-    /// Extends MetadataFileReferenceResolver to enable resolution of assembly
-    /// simple names in the GAC.
+    /// Resolves assembly identities in Global Assembly Cache.
     /// </summary>
     internal sealed class GacFileResolver : IEquatable<GacFileResolver>
     {
         /// <summary>
-        /// Architecture filter used when resolving assembly references.
+        /// Returns true if GAC is available on the platform.
         /// </summary>
-        public ImmutableArray<ProcessorArchitecture> Architectures { get; }
+        public static bool IsAvailable => CoreClrShim.AssemblyLoadContext.Type == null;
 
         /// <summary>
-        /// CultureInfo used when resolving assembly references.
+        /// Architecture filter used when resolving assembly references.
         /// </summary>
-        public CultureInfo PreferredCulture { get; }
+        public ImmutableArray<ProcessorArchitecture> Architectures { get; }
 
         /// <summary>
-        /// A resolver that is configured to resolve against the GAC associated
-        /// with the bitness of the currently executing process.
+        /// <see cref="CultureInfo"/> used when resolving assembly references, or null to prefer no culture.
         /// </summary>
-        internal static GacFileResolver Default = new GacFileResolver(
-            architectures: GlobalAssemblyCache.CurrentArchitectures,
-            preferredCulture: null);
+        public CultureInfo PreferredCulture { get; }
 
         /// <summary>
-        /// Constructs an instance of a <see cref="GacFileResolver"/>
+        /// Creates an instance of a <see cref="GacFileResolver"/>, if available on the platform (check <see cref="IsAvailable"/>).
         /// </summary>
         /// <param name="architectures">Supported architectures used to filter GAC assemblies.</param>
         /// <param name="preferredCulture">A culture to use when choosing the best assembly from 
         /// among the set filtered by <paramref name="architectures"/></param>
-        public GacFileResolver(ImmutableArray<ProcessorArchitecture> architectures, CultureInfo preferredCulture)
+        /// <exception cref="PlatformNotSupportedException">The platform doesn't support GAC.</exception>
+        public GacFileResolver(
+            ImmutableArray<ProcessorArchitecture> architectures = default(ImmutableArray<ProcessorArchitecture>), 
+            CultureInfo preferredCulture = null)
         {
+            if (!IsAvailable)
+            {
+                throw new PlatformNotSupportedException();
+            }
+
+            if (architectures.IsDefault)
+            {
+                architectures = GlobalAssemblyCache.CurrentArchitectures;
+            }
+
             Architectures = architectures;
             PreferredCulture = preferredCulture;
         }

src/Compilers/Helpers/GlobalAssemblyCacheHelpers/GlobalAssemblyCache.cs

@@ -87,13 +87,19 @@ private enum ASM_CACHE
 
         private const int ERROR_INSUFFICIENT_BUFFER = unchecked((int)0x8007007A);
 
-        public static readonly ImmutableArray<string> RootLocations;
+        public static ImmutableArray<string> s_rootLocations;
 
-        static GlobalAssemblyCache()
+        public static ImmutableArray<string> RootLocations 
         {
-            RootLocations = ImmutableArray.Create<string>(
-                GetLocation(ASM_CACHE.ROOT),
-                GetLocation(ASM_CACHE.ROOT_EX));
+            get
+            {
+                if (s_rootLocations.IsDefault)
+                {
+                    s_rootLocations = ImmutableArray.Create(GetLocation(ASM_CACHE.ROOT), GetLocation(ASM_CACHE.ROOT_EX));
+                }
+
+                return s_rootLocations;
+            }
         }
 
         private static unsafe string GetLocation(ASM_CACHE gacId)
@@ -105,7 +111,7 @@ private static unsafe string GetLocation(ASM_CACHE gacId)
                 throw Marshal.GetExceptionForHR(hr);
             }
 
-            byte[] data = new byte[((int)characterCount + 1) * 2];
+            byte[] data = new byte[(characterCount + 1) * 2];
             fixed (byte* p = data)
             {
                 hr = GetCachePath(gacId, p, ref characterCount);

src/Interactive/EditorFeatures/Core/Extensibility/Interactive/InteractiveEvaluator.cs

@@ -6,6 +6,7 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -257,9 +258,7 @@ private static MetadataReferenceResolver CreateMetadataReferenceResolver(IMetada
             return new RuntimeMetadataReferenceResolver(
                 new RelativePathResolver(searchPaths, baseDirectory),
                 string.IsNullOrEmpty(packagesDirectory) ? null : new NuGetPackageResolverImpl(packagesDirectory),
-                new GacFileResolver(
-                    architectures: GacFileResolver.Default.Architectures,  // TODO (tomat)
-                    preferredCulture: System.Globalization.CultureInfo.CurrentCulture), // TODO (tomat)
+                GacFileResolver.IsAvailable ? new GacFileResolver(preferredCulture: CultureInfo.CurrentCulture) : null,
                 (path, properties) => metadataService.GetReference(path, properties));
         }
 

src/Interactive/Features/Interactive/Core/InteractiveHost.Service.cs

@@ -169,13 +169,12 @@ private MetadataReferenceResolver CreateMetadataReferenceResolver(ImmutableArray
                 var packagesDirectory = string.IsNullOrEmpty(userProfilePath) ?
                     null :
                     Path.Combine(userProfilePath, Path.Combine(".nuget", "packages"));
+
                 return new RuntimeMetadataReferenceResolver(
-                   new RelativePathResolver(searchPaths, baseDirectory),
+                    new RelativePathResolver(searchPaths, baseDirectory),
                     string.IsNullOrEmpty(packagesDirectory) ? null : new NuGetPackageResolverImpl(packagesDirectory),
-                   new GacFileResolver(
-                       architectures: GacFileResolver.Default.Architectures,  // TODO (tomat)
-                       preferredCulture: CultureInfo.CurrentCulture), // TODO (tomat)
-                   (path, properties) => _metadataFileProvider.GetReference(path, properties));
+                    GacFileResolver.IsAvailable ? new GacFileResolver(preferredCulture: CultureInfo.CurrentCulture) : null,
+                    (path, properties) => _metadataFileProvider.GetReference(path, properties));
             }
 
             private SourceReferenceResolver CreateSourceReferenceResolver(ImmutableArray<string> searchPaths, string baseDirectory)

src/Scripting/CSharp/CommandLine/Csi.cs

@@ -23,7 +23,7 @@ internal override MetadataReferenceResolver GetCommandLineMetadataReferenceResol
             return new RuntimeMetadataReferenceResolver(
                 new RelativePathResolver(Arguments.ReferencePaths, Arguments.BaseDirectory),
                 null,
-                new GacFileResolver(GacFileResolver.Default.Architectures, CultureInfo.CurrentCulture),
+                GacFileResolver.IsAvailable ? new GacFileResolver(preferredCulture: CultureInfo.CurrentCulture) : null,
                 (path, properties) =>
                 {
                     loggerOpt?.AddRead(path);

src/Scripting/Core/Resolvers/RuntimeMetadataReferenceResolver.cs

@@ -25,7 +25,7 @@ internal sealed class RuntimeMetadataReferenceResolver : MetadataReferenceResolv
         internal RuntimeMetadataReferenceResolver(
             ImmutableArray<string> searchPaths,
             string baseDirectory)
-            : this(new RelativePathResolver(searchPaths, baseDirectory), null, GacFileResolver.Default)
+            : this(new RelativePathResolver(searchPaths, baseDirectory), null, GacFileResolver.IsAvailable ? new GacFileResolver() : null)
         {
         }
 

src/Scripting/VisualBasic/CommandLine/Vbi.vb

@@ -19,7 +19,7 @@ Namespace Microsoft.CodeAnalysis.Scripting.Hosting.VisualBasic
             Return New RuntimeMetadataReferenceResolver(
                 New RelativePathResolver(Arguments.ReferencePaths, Arguments.BaseDirectory),
                 Nothing,
-                New GacFileResolver(GacFileResolver.Default.Architectures, CultureInfo.CurrentCulture),
+                If(GacFileResolver.IsAvailable, New GacFileResolver(preferredCulture:=CultureInfo.CurrentCulture), Nothing),
                 Function(path, properties)
                     loggerOpt?.AddRead(path)
                     Return MetadataReference.CreateFromFile(path)