Update logic to find compilers

src/RoslynCodeTaskFactory.UnitTests/RoslynCodeTaskFactory.UnitTests.csproj

@@ -19,4 +19,8 @@
     <ProjectReference Include="..\RoslynCodeTaskFactory\RoslynCodeTaskFactory.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
+  </ItemGroup>
+
 </Project>

src/RoslynCodeTaskFactory/CodeTaskFactory.cs

@@ -4,9 +4,11 @@
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Threading;
 using System.Xml;
 using System.Xml.Linq;
 
@@ -160,6 +162,8 @@ public TaskPropertyInfo[] GetTaskParameters()
         /// <inheritdoc cref="ITaskFactory.Initialize"/>
         public bool Initialize(string taskName, IDictionary<string, TaskPropertyInfo> parameterGroup, string taskBody, IBuildEngine taskFactoryLoggingHost)
         {
+            WaitForDebuggerIfConfigured();
+
             _log = new TaskLoggingHelper(taskFactoryLoggingHost, taskName)
             {
                 TaskResources = Strings.ResourceManager,
@@ -807,5 +811,27 @@ private bool TryCompileInMemoryAssembly(IBuildEngine buildEngine, TaskInfo taskI
                 }
             }
         }
+
+        /// <summary>
+        /// Waits for a user to attach a debugger.
+        /// </summary>
+        private void WaitForDebuggerIfConfigured()
+        {
+            if (!String.Equals(Environment.GetEnvironmentVariable("ROSLYNCODETASKFACTORY_DEBUG"), "1"))
+            {
+                return;
+            }
+
+            Process currentProcess = Process.GetCurrentProcess();
+
+            Console.WriteLine(Strings.CodeTaskFactory_WaitingForDebugger, currentProcess.MainModule.FileName, currentProcess.Id);
+
+            while (!Debugger.IsAttached)
+            {
+                Thread.Sleep(200);
+            }
+
+            Debugger.Break();
+        }
     }
 }

src/RoslynCodeTaskFactory/Internal/ManagedCompiler.cs

@@ -1,13 +1,38 @@
-using System;
-using System.IO;
-using Microsoft.Build.Framework;
+using Microsoft.Build.Framework;
 using Microsoft.Build.Tasks;
 using Microsoft.Build.Utilities;
+using System;
+using System.IO;
+using System.Linq;
 
 namespace RoslynCodeTaskFactory.Internal
 {
     internal abstract class ManagedCompiler : ToolTask
     {
+        private static readonly string DotnetCliPath = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH");
+
+        private readonly Lazy<string> _executablePath;
+
+        protected ManagedCompiler()
+        {
+            _executablePath = new Lazy<string>(() =>
+            {
+                string pathToBuildTools = ToolLocationHelper.GetPathToBuildTools(ToolLocationHelper.CurrentToolsVersion, DotNetFrameworkArchitecture.Bitness32);
+
+                Func<string>[] possibleLocations =
+                {
+                    // Standard MSBuild and legacy .NET Core
+                    () => Path.Combine(pathToBuildTools, "Roslyn", ToolName),
+                    // Legacy .NET Core
+                    () => Path.Combine(pathToBuildTools, "Roslyn", Path.ChangeExtension(ToolName, ".dll")),
+                    // .NET Core 2.0
+                    () => Path.Combine(pathToBuildTools, "Roslyn", "bincore", Path.ChangeExtension(ToolName, ".dll")),
+                };
+
+                return possibleLocations.Select(possibleLocation => possibleLocation()).FirstOrDefault(File.Exists);
+            }, isThreadSafe: true);
+        }
+
         public bool? Deterministic { get; set; }
 
         public bool? NoConfig { get; set; }
@@ -26,6 +51,8 @@ internal abstract class ManagedCompiler : ToolTask
 
         public bool? UseSharedCompilation { get; set; }
 
+        protected bool IsDotnetCli => !String.IsNullOrWhiteSpace(DotnetCliPath);
+
         protected internal virtual void AddResponseFileCommands(CommandLineBuilderExtension commandLine)
         {
             commandLine.AppendPlusOrMinusSwitch("/deterministic", Deterministic);
@@ -45,6 +72,13 @@ protected override string GenerateCommandLineCommands()
         {
             CommandLineBuilderExtension commandLineBuilder = new CommandLineBuilderExtension();
 
+            if (IsDotnetCli)
+            {
+                commandLineBuilder.AppendFileNameIfNotNull(_executablePath.Value);
+
+                commandLineBuilder.AppendTextUnquoted(" ");
+            }
+
             AddCommandLineCommands(commandLineBuilder);
 
             return commandLineBuilder.ToString();
@@ -57,19 +91,12 @@ protected override string GenerateFullPathToTool()
                 return ToolExe;
             }
 
-            string pathToBuildTools = ToolLocationHelper.GetPathToBuildTools(ToolLocationHelper.CurrentToolsVersion, DotNetFrameworkArchitecture.Bitness32);
-
-            if (pathToBuildTools != null)
+            if (IsDotnetCli)
             {
-                string toolMSBuildLocation = Path.Combine(pathToBuildTools, "Roslyn", ToolName);
-
-                if (File.Exists(toolMSBuildLocation))
-                {
-                    return toolMSBuildLocation;
-                }
+                return DotnetCliPath;
             }
 
-            return null;
+            return _executablePath.Value;
         }
 
         protected override string GenerateResponseFileCommands()

src/RoslynCodeTaskFactory/Strings.resx

@@ -159,4 +159,7 @@
     <value>MSB3428: You must specify source code within the Code element or a path to a file containing source code.</value>
     <comment>{StrBegin="MSB3428: "}</comment>
   </data>
+  <data name="CodeTaskFactory_WaitingForDebugger" xml:space="preserve">
+    <value>Waiting for debugger to attach ({0} PID {1}).  Press enter to continue...</value>
+  </data>
 </root>