Launch the build host process and run design-time builds in it

This implements the basic launching of the build hsot process, setting
up the RPC channel, and running the design-time builds in that process.
Right now this only works for .NET Core projects.

src/Features/LanguageServer/Microsoft.CodeAnalysis.LanguageServer/HostWorkspace/BuildHostProcessManager.cs

@@ -0,0 +1,111 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using System.Threading;
+using Microsoft.CodeAnalysis.Workspaces.MSBuild.BuildHost;
+using Roslyn.Utilities;
+using StreamJsonRpc;
+
+namespace Microsoft.CodeAnalysis.LanguageServer.HostWorkspace;
+
+internal sealed class BuildHostProcessManager : IDisposable
+{
+    private readonly SemaphoreSlim _gate = new(initialCount: 1);
+    private BuildHostProcess? _process;
+
+    public async Task<IBuildHost> GetBuildHostAsync(CancellationToken cancellationToken)
+    {
+        using (await _gate.DisposableWaitAsync(cancellationToken).ConfigureAwait(false))
+        {
+            if (_process == null)
+            {
+                _process = new BuildHostProcess(LaunchDotNetCoreBuildHost());
+                _process.Disconnected += BuildHostProcess_Disconnected;
+            }
+
+            return _process.BuildHost;
+        }
+    }
+
+#pragma warning disable VSTHRD100 // Avoid async void methods: We're responding to Process.Exited, so an async void event handler is all we can do
+    private async void BuildHostProcess_Disconnected(object? sender, EventArgs e)
+#pragma warning restore VSTHRD100 // Avoid async void methods
+    {
+        Contract.ThrowIfNull(sender, $"{nameof(BuildHostProcess)}.{nameof(BuildHostProcess.Disconnected)} was raised with a null sender.");
+
+        using (await _gate.DisposableWaitAsync().ConfigureAwait(false))
+        {
+            if (_process == sender)
+            {
+                _process.Dispose();
+                _process = null;
+            }
+        }
+    }
+
+    private static Process LaunchDotNetCoreBuildHost()
+    {
+        var processStartInfo = new ProcessStartInfo()
+        {
+            FileName = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "dotnet.exe" : "dotnet",
+            CreateNoWindow = true,
+            UseShellExecute = false,
+            RedirectStandardInput = true,
+            RedirectStandardOutput = true,
+        };
+
+        // We need to roll forward to the latest runtime, since the project may be using an SDK (or an SDK required runtime) newer than we ourselves built with.
+        // We set the environment variable since --roll-forward LatestMajor doesn't roll forward to prerelease SDKs otherwise.
+        processStartInfo.ArgumentList.Add("--roll-forward");
+        processStartInfo.ArgumentList.Add("LatestMajor");
+        processStartInfo.Environment["DOTNET_ROLL_FORWARD_TO_PRERELEASE"] = "1";
+
+        processStartInfo.ArgumentList.Add(typeof(IBuildHost).Assembly.Location);
+        var process = Process.Start(processStartInfo);
+        Contract.ThrowIfNull(process, "Process.Start failed to launch a process.");
+        return process;
+    }
+
+    public void Dispose()
+    {
+        _process?.Dispose();
+    }
+
+    private sealed class BuildHostProcess : IDisposable
+    {
+        private readonly Process _process;
+        private readonly JsonRpc _jsonRpc;
+
+        public BuildHostProcess(Process process)
+        {
+            _process = process;
+
+            _process.EnableRaisingEvents = true;
+            _process.Exited += Process_Exited;
+
+            var messageHandler = new HeaderDelimitedMessageHandler(sendingStream: _process.StandardInput.BaseStream, receivingStream: _process.StandardOutput.BaseStream, new JsonMessageFormatter());
+
+            _jsonRpc = new JsonRpc(messageHandler);
+            _jsonRpc.StartListening();
+            BuildHost = _jsonRpc.Attach<IBuildHost>();
+        }
+
+        private void Process_Exited(object? sender, EventArgs e)
+        {
+            Disconnected?.Invoke(this, EventArgs.Empty);
+        }
+
+        public IBuildHost BuildHost { get; }
+
+        public event EventHandler? Disconnected;
+
+        public void Dispose()
+        {
+            _jsonRpc.Dispose();
+        }
+    }
+}
+

src/Features/LanguageServer/Microsoft.CodeAnalysis.LanguageServer/HostWorkspace/LanguageServerProjectSystem.cs

@@ -143,7 +143,7 @@ private async Task<bool> TryEnsureMSBuildLoadedAsync(string workingDirectory)
                 if (msbuildInstance != null)
                 {
                     MSBuildLocator.RegisterInstance(msbuildInstance);
-                    _logger.LogInformation($"Loaded MSBuild at {msbuildInstance.MSBuildPath}");
+                    _logger.LogInformation($"Loaded MSBuild in-process from {msbuildInstance.MSBuildPath}");
                     _msbuildLoaded = true;
 
                     return true;
@@ -164,9 +164,7 @@ private async ValueTask LoadOrReloadProjectsAsync(ImmutableSegmentedList<string>
         var stopwatch = Stopwatch.StartNew();
 
         // TODO: support configuration switching
-        var projectBuildManager = new ProjectBuildManager(additionalGlobalProperties: ImmutableDictionary<string, string>.Empty);
-
-        projectBuildManager.StartBatchBuild();
+        using var buildHostProcessManager = new BuildHostProcessManager();
 
         var displayedToast = 0;
 
@@ -178,7 +176,7 @@ private async ValueTask LoadOrReloadProjectsAsync(ImmutableSegmentedList<string>
             {
                 tasks.Add(Task.Run(async () =>
                 {
-                    var errorKind = await LoadOrReloadProjectAsync(projectPathToLoadOrReload, projectBuildManager, cancellationToken);
+                    var errorKind = await LoadOrReloadProjectAsync(projectPathToLoadOrReload, buildHostProcessManager, cancellationToken);
                     if (errorKind is LSP.MessageType.Error)
                     {
                         // We should display a toast when the value of displayedToast is 0.  This will also update the value to 1 meaning we won't send any more toasts.
@@ -196,19 +194,19 @@ private async ValueTask LoadOrReloadProjectsAsync(ImmutableSegmentedList<string>
         }
         finally
         {
-            projectBuildManager.EndBatchBuild();
-
             _logger.LogInformation($"Completed (re)load of all projects in {stopwatch.Elapsed}");
         }
     }
 
-    private async Task<LSP.MessageType?> LoadOrReloadProjectAsync(string projectPath, ProjectBuildManager projectBuildManager, CancellationToken cancellationToken)
+    private async Task<LSP.MessageType?> LoadOrReloadProjectAsync(string projectPath, BuildHostProcessManager buildHostProcessManager, CancellationToken cancellationToken)
     {
         try
         {
-            if (_projectFileLoaderRegistry.TryGetLoaderFromProjectPath(projectPath, out var loader))
+            var buildHost = await buildHostProcessManager.GetBuildHostAsync(cancellationToken);
+
+            if (await buildHost.IsProjectFileSupportedAsync(projectPath, cancellationToken))
             {
-                var loadedFile = await loader.LoadProjectFileAsync(projectPath, projectBuildManager, cancellationToken);
+                var loadedFile = await buildHost.LoadProjectFileAsync(projectPath, cancellationToken);
                 var loadedProjectInfos = await loadedFile.GetProjectFileInfosAsync(cancellationToken);
 
                 var existingProjects = _loadedProjects.GetOrAdd(projectPath, static _ => new List<LoadedProject>());
@@ -241,15 +239,17 @@ private async ValueTask LoadOrReloadProjectsAsync(ImmutableSegmentedList<string>
                     }
                 }
 
-                if (loadedFile.Log.Any())
+                var diagnosticLogItems = await loadedFile.GetDiagnosticLogItemsAsync(cancellationToken);
+
+                if (diagnosticLogItems.Any())
                 {
-                    foreach (var logItem in loadedFile.Log)
+                    foreach (var logItem in diagnosticLogItems)
                     {
                         var projectName = Path.GetFileName(projectPath);
                         _logger.Log(logItem.Kind is WorkspaceDiagnosticKind.Failure ? LogLevel.Error : LogLevel.Warning, $"{logItem.Kind} while loading {logItem.ProjectFilePath}: {logItem.Message}");
                     }
 
-                    return loadedFile.Log.Any(logItem => logItem.Kind is WorkspaceDiagnosticKind.Failure) ? LSP.MessageType.Error : LSP.MessageType.Warning;
+                    return diagnosticLogItems.Any(logItem => logItem.Kind is WorkspaceDiagnosticKind.Failure) ? LSP.MessageType.Error : LSP.MessageType.Warning;
                 }
                 else
                 {

src/Workspaces/Core/MSBuild.BuildHost/BuildHost.cs

@@ -0,0 +1,45 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.MSBuild;
+using Microsoft.CodeAnalysis.MSBuild.Build;
+using Roslyn.Utilities;
+using StreamJsonRpc;
+
+namespace Microsoft.CodeAnalysis.Workspaces.MSBuild.BuildHost;
+
+internal sealed class BuildHost : IBuildHost
+{
+    private readonly JsonRpc _jsonRpc;
+    private readonly ProjectFileLoaderRegistry _projectFileLoaderRegistry;
+    private readonly ProjectBuildManager _buildManager;
+
+    public BuildHost(JsonRpc jsonRpc, SolutionServices solutionServices)
+    {
+        _jsonRpc = jsonRpc;
+        _projectFileLoaderRegistry = new ProjectFileLoaderRegistry(solutionServices, new DiagnosticReporter(new AdhocWorkspace()));
+        _buildManager = new ProjectBuildManager(System.Collections.Immutable.ImmutableDictionary<string, string>.Empty);
+        _buildManager.StartBatchBuild();
+    }
+
+    public Task<bool> IsProjectFileSupportedAsync(string projectFilePath, CancellationToken cancellationToken)
+    {
+        return Task.FromResult(_projectFileLoaderRegistry.TryGetLoaderFromProjectPath(projectFilePath, DiagnosticReportingMode.Ignore, out var _));
+    }
+
+    public async Task<IRemoteProjectFile> LoadProjectFileAsync(string projectFilePath, CancellationToken cancellationToken)
+    {
+        Contract.ThrowIfFalse(_projectFileLoaderRegistry.TryGetLoaderFromProjectPath(projectFilePath, out var projectLoader));
+        return new RemoteProjectFile(await projectLoader.LoadProjectFileAsync(projectFilePath, _buildManager, cancellationToken).ConfigureAwait(false));
+    }
+
+    public void Shutdown()
+    {
+        _buildManager.EndBatchBuild();
+        _jsonRpc.Dispose();
+    }
+}

src/Workspaces/Core/MSBuild.BuildHost/IBuildHost.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.CodeAnalysis.Workspaces.MSBuild.BuildHost;
+
+/// <summary>
+/// The RPC interface implemented by this host; called via JSON-RPC.
+/// </summary>
+internal interface IBuildHost
+{
+    /// <summary>
+    /// Returns whether this project's language is supported.
+    /// </summary>
+    Task<bool> IsProjectFileSupportedAsync(string path, CancellationToken cancellationToken);
+
+    Task<IRemoteProjectFile> LoadProjectFileAsync(string path, CancellationToken cancellationToken);
+
+    void Shutdown();
+}

src/Workspaces/Core/MSBuild.BuildHost/IRemoteProjectFile.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Immutable;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.MSBuild;
+using Microsoft.CodeAnalysis.MSBuild.Logging;
+using StreamJsonRpc;
+
+namespace Microsoft.CodeAnalysis.Workspaces.MSBuild.BuildHost;
+
+/// <summary>
+/// A trimmed down interface of <see cref="IProjectFile"/> that is usable for RPC to the build host process and meets all the requirements of being an <see cref="RpcMarshalableAttribute"/> interface.
+/// </summary>
+[RpcMarshalable]
+internal interface IRemoteProjectFile : IDisposable
+{
+    Task<ImmutableArray<ProjectFileInfo>> GetProjectFileInfosAsync(CancellationToken cancellationToken);
+    Task<ImmutableArray<DiagnosticLogItem>> GetDiagnosticLogItemsAsync(CancellationToken cancellationToken);
+}

src/Workspaces/Core/MSBuild.BuildHost/MSBuild/Logging/DiagnosticLogItem.cs

@@ -3,13 +3,20 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Runtime.Serialization;
 
 namespace Microsoft.CodeAnalysis.MSBuild.Logging
 {
+    [DataContract]
     internal class DiagnosticLogItem
     {
+        [DataMember(Order = 0)]
         public WorkspaceDiagnosticKind Kind { get; }
+
+        [DataMember(Order = 1)]
         public string Message { get; }
+
+        [DataMember(Order = 2)]
         public string ProjectFilePath { get; }
 
         public DiagnosticLogItem(WorkspaceDiagnosticKind kind, string message, string projectFilePath)

src/Workspaces/Core/MSBuild.BuildHost/MSBuild/ProjectFile/DocumentFileInfo.cs

@@ -2,39 +2,47 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Runtime.Serialization;
+
 namespace Microsoft.CodeAnalysis.MSBuild
 {
     /// <summary>
     /// Represents a source file that is part of a project file.
     /// </summary>
+    [DataContract]
     internal sealed class DocumentFileInfo
     {
         /// <summary>
         /// The absolute path to the document file on disk.
         /// </summary>
+        [DataMember(Order = 0)]
         public string FilePath { get; }
 
         /// <summary>
         /// A fictional path to the document, relative to the project.
         /// The document may not actually exist at this location, and is used
         /// to represent linked documents. This includes the file name.
         /// </summary>
+        [DataMember(Order = 1)]
         public string LogicalPath { get; }
 
         /// <summary>
         /// True if the document has a logical path that differs from its 
         /// absolute file path.
         /// </summary>
+        [DataMember(Order = 2)]
         public bool IsLinked { get; }
 
         /// <summary>
         /// True if the file was generated during build.
         /// </summary>
+        [DataMember(Order = 3)]
         public bool IsGenerated { get; }
 
         /// <summary>
         /// The <see cref="SourceCodeKind"/> of this document.
         /// </summary>
+        [DataMember(Order = 4)]
         public SourceCodeKind SourceCodeKind { get; }
 
         public DocumentFileInfo(string filePath, string logicalPath, bool isLinked, bool isGenerated, SourceCodeKind sourceCodeKind)