Remove custom assembly resolution

The custom assembly resolution is no longer needed in our MSBuild task
now that it has no project references and multi-targets to the important
runtimes.

This logic has actually been broken for some time now. More recent
changes revealed it's just not necessary.

src/Compilers/Core/MSBuildTask/AssemblyResolution.cs

-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
-
-using Microsoft.CodeAnalysis.CommandLine;
-using Roslyn.Utilities;
-using System;
-using System.Diagnostics;
-using System.IO;
-using System.Reflection;
-
-namespace Microsoft.CodeAnalysis.BuildTasks
-{
-    // TODO: Remove once https://github.com/Microsoft/msbuild/issues/1309 is fixed.
-
-    /// <summary>
-    /// msbuild currently doesn't support specifying binding redirects per custom task thru a config file. 
-    /// Each task needs to handle version redirection of its dependencies manually. 
-    /// </summary>
-    internal static class AssemblyResolution
-    {
-        static AssemblyResolution()
-        {
-#if NET472 || NETCOREAPP2_1
-            AppDomain.CurrentDomain.AssemblyResolve += ResolveAssembly;
-#else
-#error Unrecoginzed configuration
-#endif
-        }
-
-        public static void Install()
-        {
-            // empty, just to trigger static ctor
-        }
-
-        internal static Assembly ResolveAssembly(object sender, ResolveEventArgs e) => ResolveAssembly(e.Name, e.RequestingAssembly);
-
-        internal static Assembly ResolveAssembly(string assemblyDisplayName, Assembly requestingAssemblyOpt)
-        {
-            var name = new AssemblyName(assemblyDisplayName);
-            try
-            {
-                return TryRedirect(name) ? LoadAssemblyWithRedirects(name) : null;
-            }
-            catch
-            {
-                ValidateBootstrapUtil.AddFailedLoad(name);
-                throw;
-            }
-        }
-
-        private static readonly byte[] s_b03f5f7f11d50a3a = new byte[] { 0xb0, 0x3f, 0x5f, 0x7f, 0x11, 0xd5, 0x0a, 0x3a };
-        private static readonly byte[] s_b77a5c561934e089 = new byte[] { 0xb7, 0x7a, 0x5c, 0x56, 0x19, 0x34, 0xe0, 0x89 };
-
-        private static bool TryRedirect(AssemblyName name)
-        {
-            switch (name.Name)
-            {
-                case "System.IO.Compression":
-                    return TryRedirect(name, s_b77a5c561934e089, 4, 1, 2, 0);
-
-                case "System.Console":
-                case "System.IO.Pipes":
-                case "System.Security.AccessControl":
-                case "System.Security.Cryptography.Primitives":
-                case "System.Security.Principal.Windows":
-                case "System.Threading.Thread":
-                    return TryRedirect(name, s_b03f5f7f11d50a3a, 4, 0, 1, 0);
-
-                case "System.IO.FileSystem":
-                case "System.IO.FileSystem.Primitives":
-                    return TryRedirect(name, s_b03f5f7f11d50a3a, 4, 0, 2, 0);
-
-                case "System.Diagnostics.Process":
-                case "System.Diagnostics.StackTrace":
-                    return TryRedirect(name, s_b03f5f7f11d50a3a, 4, 0, 3, 0);
-
-                case "System.Reflection":
-                    return TryRedirect(name, s_b03f5f7f11d50a3a, 4, 1, 1, 0);
-
-                // Assemblies in the runtimes directory. We're not concerned about
-                // redirecting versions for these assemblies, only location, so
-                // it's fine to always return true. The loading location override is
-                // found in the LoadAssemblyWithRedirects method.
-                case "System.IO.Pipes.AccessControl":
-                    return true;
-            }
-
-            return false;
-        }
-
-        private static Assembly LoadAssemblyWithRedirects(AssemblyName name)
-        {
-            // Check if we need to redirect the location of this assembly. This
-            // is necessary for assemblies in the runtimes/ subdirectory of the
-            // build task as this directory is not searched for dependencies by
-            // default. This is necessary because the CoreCLR shared loader doesn't
-            // provide a mechanism for nested assembly load policy:
-            // https://github.com/dotnet/coreclr/issues/15982
-            switch (name.Name)
-            {
-                case "System.IO.Pipes.AccessControl":
-                    var assembly = TryRedirectToRuntimesDir(name);
-                    if (assembly != null)
-                    {
-                        return assembly;
-                    }
-                    break;
-            }
-
-            return Assembly.Load(name);
-        }
-
-        private static bool TryRedirect(AssemblyName name, byte[] token, int major, int minor, int build, int revision)
-        {
-            var version = new Version(major, minor, build, revision);
-            if (KeysEqual(name.GetPublicKeyToken(), token) && name.Version < version)
-            {
-                name.Version = version;
-                return true;
-            }
-
-            return false;
-        }
-
-        private static readonly string s_assemblyLocation = Utilities.TryGetAssemblyPath(typeof(AssemblyResolution).GetTypeInfo().Assembly);
-        private static Assembly TryRedirectToRuntimesDir(AssemblyName name)
-        {
-            CompilerServerLogger.Log($"Loading with redirect {name.Name}");
-            if (s_assemblyLocation == null)
-            {
-                return null;
-            }
-
-            var taskDir = Path.GetDirectoryName(s_assemblyLocation);
-            var osId = PlatformInformation.IsWindows ? "win" : "unix";
-            var runtimeDir = Path.Combine(taskDir, "runtimes", osId, "lib", "netstandard1.3");
-
-            var assemblyPath = Path.Combine(runtimeDir, name.Name) + ".dll";
-
-            if (File.Exists(assemblyPath))
-            {
-                CompilerServerLogger.Log($"Loading from: {assemblyPath}");
-                return LoadAssemblyFromPath(assemblyPath);
-            }
-
-            CompilerServerLogger.Log($"File not found: {assemblyPath}");
-
-            return null;
-
-            Assembly LoadAssemblyFromPath(string path)
-                => (Assembly)typeof(Assembly).GetTypeInfo()
-                    .GetDeclaredMethod("LoadFile")
-                    ?.Invoke(null, parameters: new object[] { assemblyPath });
-        }
-
-        private static bool KeysEqual(byte[] left, byte[] right)
-        {
-            if (left.Length != right.Length)
-            {
-                return false;
-            }
-
-            for (var i = 0; i < left.Length; i++)
-            {
-                if (left[i] != right[i])
-                {
-                    return false;
-                }
-            }
-
-            return true;
-        }
-    }
-}

src/Compilers/Core/MSBuildTask/CopyRefAssembly.cs

@@ -20,11 +20,6 @@ public sealed class CopyRefAssembly : Task
         [Required]
         public string DestinationPath { get; set; }
 
-        static CopyRefAssembly()
-        {
-            AssemblyResolution.Install();
-        }
-
         public CopyRefAssembly()
         {
             TaskResources = ErrorString.ResourceManager;

src/Compilers/Core/MSBuildTask/ManagedCompiler.cs

@@ -26,11 +26,6 @@ public abstract class ManagedCompiler : ManagedToolTask
 
         internal abstract RequestLanguage Language { get; }
 
-        static ManagedCompiler()
-        {
-            AssemblyResolution.Install();
-        }
-
         public ManagedCompiler()
         {
             TaskResources = ErrorString.ResourceManager;