Fix multi-target

Use multi-target instead of reflection

src/Compilers/Core/MSBuildTask/ManagedToolTask.cs

@@ -80,21 +80,28 @@ protected sealed override string GenerateFullPathToTool()
         /// as the implementation of IsManagedTool calls this property. See the comment in
         /// <see cref="ManagedCompiler.HasToolBeenOverridden"/>.
         /// </remarks>
-        protected sealed override string ToolName
-            => $"{ToolNameWithoutExtension}.{(CoreClrShim.IsRunningOnCoreClr ? "dll" : "exe")}";
+        protected sealed override string ToolName => $"{ToolNameWithoutExtension}.{ToolExtension}";
+
+        private static string ToolExtension =>
+#if NETCOREAPP2_1
+            "dll";
+#elif NET472
+            "exe";
+#else
+#error Unrecognized framework
+#endif
 
         private static bool IsCliHost(out string pathToDotnet)
         {
-            if (CoreClrShim.IsRunningOnCoreClr)
-            {
-                pathToDotnet = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH");
-                return !string.IsNullOrEmpty(pathToDotnet);
-            }
-            else
-            {
-                pathToDotnet = null;
-                return false;
-            }
+#if NETCOREAPP2_1
+            pathToDotnet = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH");
+            return !string.IsNullOrEmpty(pathToDotnet);
+#elif NET472
+            pathToDotnet = null;
+            return false;
+#else
+#error Unrecognized framework
+#endif
         }
 
         private static string PrependFileToArgs(string pathToTool, string commandLineArgs)

src/Compilers/Shared/BuildServerConnection.cs

@@ -374,32 +374,30 @@ internal static bool IsCompilerServerSupported(string tempPath)
 
         internal static bool TryCreateServerCore(string clientDir, string pipeName)
         {
-            bool isRunningOnCoreClr = CoreClrShim.IsRunningOnCoreClr;
             string expectedPath;
             string processArguments;
-            if (isRunningOnCoreClr)
-            {
-                // The server should be in the same directory as the client
-                var expectedCompilerPath = Path.Combine(clientDir, ServerNameCoreClr);
-                expectedPath = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH") ?? "dotnet";
-                processArguments = $@"""{expectedCompilerPath}"" ""-pipename:{pipeName}""";
+#if NETCOREAPP2_1
+            // The server should be in the same directory as the client
+            var expectedCompilerPath = Path.Combine(clientDir, ServerNameCoreClr);
+            expectedPath = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH") ?? "dotnet";
+            processArguments = $@"""{expectedCompilerPath}"" ""-pipename:{pipeName}""";
 
-                if (!File.Exists(expectedCompilerPath))
-                {
-                    return false;
-                }
-            }
-            else
+            if (!File.Exists(expectedCompilerPath))
             {
-                // The server should be in the same directory as the client
-                expectedPath = Path.Combine(clientDir, ServerNameDesktop);
-                processArguments = $@"""-pipename:{pipeName}""";
+                return false;
+            }
+#elif NET472
+            // The server should be in the same directory as the client
+            expectedPath = Path.Combine(clientDir, ServerNameDesktop);
+            processArguments = $@"""-pipename:{pipeName}""";
 
-                if (!File.Exists(expectedPath))
-                {
-                    return false;
-                }
+            if (!File.Exists(expectedPath))
+            {
+                return false;
             }
+#else
+#error Unrecognized configuration
+#endif
 
             if (PlatformInformation.IsWindows)
             {

src/Test/Utilities/Portable/Compilation/RuntimeUtilities.cs

@@ -15,6 +15,18 @@ namespace Microsoft.CodeAnalysis.Test.Utilities
     /// </summary>
     public static partial class RuntimeUtilities
     {
+        internal static bool IsDesktopRuntime =>
+#if NET472
+            true;
+#elif NETCOREAPP2_1
+            false;
+#elif NETSTANDARD2_0
+            throw new PlatformNotSupportedException();
+#else
+#error Unsupported configuration
+#endif
+        internal static bool IsCoreClrRuntime => !IsDesktopRuntime;
+
         internal static BuildPaths CreateBuildPaths(string workingDirectory, string sdkDirectory = null, string tempDirectory = null)
         {
             tempDirectory = tempDirectory ?? Path.GetTempPath();

src/Test/Utilities/Portable/TargetFrameworkUtil.cs

@@ -5,6 +5,7 @@
 using System.Collections.Immutable;
 using System.Text;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Test.Utilities;
 using static TestReferences;
 
 namespace Roslyn.Test.Utilities
@@ -55,7 +56,7 @@ public enum TargetFramework
 
     public static class TargetFrameworkUtil
     {
-        public static MetadataReference StandardCSharpReference => CoreClrShim.IsRunningOnCoreClr ? NetStandard20.MicrosoftCSharpRef : TestBase.CSharpDesktopRef;
+        public static MetadataReference StandardCSharpReference => RuntimeUtilities.IsCoreClrRuntime ? NetStandard20.MicrosoftCSharpRef : TestBase.CSharpDesktopRef;
 
         /*
          * ⚠ Dev note ⚠: properties in TestBase are backed by Lazy<T>. Avoid changes to the following properties
@@ -78,10 +79,10 @@ public static class TargetFrameworkUtil
         public static ImmutableArray<MetadataReference> Mscorlib461ExtendedReferences => ImmutableArray.Create<MetadataReference>(Net461.mscorlibRef, Net461.SystemRef, Net461.SystemCoreRef, Net461.SystemValueTupleRef, Net461.SystemRuntimeRef);
         public static ImmutableArray<MetadataReference> NetStandard20References => ImmutableArray.Create<MetadataReference>(NetStandard20.NetStandard, NetStandard20.MscorlibRef, NetStandard20.SystemRuntimeRef, NetStandard20.SystemCoreRef, NetStandard20.SystemDynamicRuntimeRef);
         public static ImmutableArray<MetadataReference> WinRTReferences => ImmutableArray.Create(TestBase.WinRtRefs);
-        public static ImmutableArray<MetadataReference> StandardReferences => CoreClrShim.IsRunningOnCoreClr ? NetStandard20References : Mscorlib46ExtendedReferences;
+        public static ImmutableArray<MetadataReference> StandardReferences => RuntimeUtilities.IsCoreClrRuntime ? NetStandard20References : Mscorlib46ExtendedReferences;
         public static ImmutableArray<MetadataReference> StandardAndCSharpReferences => StandardReferences.Add(StandardCSharpReference);
-        public static ImmutableArray<MetadataReference> StandardAndVBRuntimeReferences => CoreClrShim.IsRunningOnCoreClr ? NetStandard20References.Add(NetStandard20.MicrosoftVisualBasicRef) : Mscorlib46ExtendedReferences.Add(TestBase.MsvbRef_v4_0_30319_17929);
-        public static ImmutableArray<MetadataReference> StandardCompatReferences => CoreClrShim.IsRunningOnCoreClr ? NetStandard20References : Mscorlib40References;
+        public static ImmutableArray<MetadataReference> StandardAndVBRuntimeReferences => RuntimeUtilities.IsCoreClrRuntime ? NetStandard20References.Add(NetStandard20.MicrosoftVisualBasicRef) : Mscorlib46ExtendedReferences.Add(TestBase.MsvbRef_v4_0_30319_17929);
+        public static ImmutableArray<MetadataReference> StandardCompatReferences => RuntimeUtilities.IsCoreClrRuntime ? NetStandard20References : Mscorlib40References;
         public static ImmutableArray<MetadataReference> DefaultVbReferencs => ImmutableArray.Create(TestBase.MscorlibRef, TestBase.SystemRef, TestBase.SystemCoreRef, TestBase.MsvbRef);
 
         public static ImmutableArray<MetadataReference> GetReferences(TargetFramework tf)

src/Test/Utilities/Portable/TestBase.cs

@@ -76,7 +76,7 @@ private static MetadataReference GetOrCreateMetadataReference(ref MetadataRefere
             LazyThreadSafetyMode.PublicationOnly);
         public static MetadataReference[] LatestVbReferences => s_lazyLatestVbReferences.Value;
 
-        public static readonly AssemblyName RuntimeCorLibName = CoreClrShim.IsRunningOnCoreClr
+        public static readonly AssemblyName RuntimeCorLibName = RuntimeUtilities.IsCoreClrRuntime
             ? new AssemblyName("netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51")
             : new AssemblyName("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089");