Support creating binlogs for the language server's design time builds

This allows you to configure a directory where we will write binlogs
for any design time builds. This is only needed when debugging project
system issues, but when you need this, you really need this.

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

@@ -8,10 +8,12 @@
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using Microsoft.Build.Locator;
+using Microsoft.Build.Logging;
 using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.MSBuild;
 using Microsoft.CodeAnalysis.MSBuild.Build;
+using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.ProjectSystem;
 using Microsoft.CodeAnalysis.Shared.TestHooks;
 using Microsoft.CodeAnalysis.Workspaces.ProjectSystem;
@@ -32,13 +34,23 @@ internal sealed class LanguageServerProjectSystem
     /// This is just we don't have code simultaneously trying to load and unload solutions at once.
     /// </summary>
     private readonly SemaphoreSlim _gate = new SemaphoreSlim(initialCount: 1);
-
     private bool _msbuildLoaded = false;
 
+    /// <summary>
+    /// The suffix to use for the binary log name; incremented each time we have a new build. Should be incremented with <see cref="Interlocked.Increment(ref int)"/>.
+    /// </summary>
+    private int _binaryLogNumericSuffix;
+
+    /// <summary>
+    /// A GUID put into all binary log file names, so that way one session doesn't accidentally overwrite the logs from a prior session.
+    /// </summary>
+    private readonly Guid _binaryLogGuidSuffix = Guid.NewGuid();
+
     private readonly AsyncBatchingWorkQueue<string> _projectsToLoadAndReload;
 
     private readonly LanguageServerWorkspaceFactory _workspaceFactory;
     private readonly IFileChangeWatcher _fileChangeWatcher;
+    private readonly IGlobalOptionService _globalOptionService;
     private readonly ILogger _logger;
 
     /// <summary>
@@ -54,11 +66,13 @@ internal sealed class LanguageServerProjectSystem
     public LanguageServerProjectSystem(
         LanguageServerWorkspaceFactory workspaceFactory,
         IFileChangeWatcher fileChangeWatcher,
+        IGlobalOptionService globalOptionService,
         ILoggerFactory loggerFactory,
         IAsynchronousOperationListenerProvider listenerProvider)
     {
         _workspaceFactory = workspaceFactory;
         _fileChangeWatcher = fileChangeWatcher;
+        _globalOptionService = globalOptionService;
         _logger = loggerFactory.CreateLogger(nameof(LanguageServerProjectSystem));
 
         // TODO: remove the DiagnosticReporter that's coupled to the Workspace here
@@ -164,7 +178,7 @@ private async ValueTask LoadOrReloadProjectsAsync(ImmutableSegmentedList<string>
         var stopwatch = Stopwatch.StartNew();
 
         // TODO: support configuration switching
-        var projectBuildManager = new ProjectBuildManager(additionalGlobalProperties: ImmutableDictionary<string, string>.Empty);
+        var projectBuildManager = new ProjectBuildManager(additionalGlobalProperties: ImmutableDictionary<string, string>.Empty, msbuildLogger: CreateMSBuildLogger());
 
         projectBuildManager.StartBatchBuild();
 
@@ -202,6 +216,19 @@ private async ValueTask LoadOrReloadProjectsAsync(ImmutableSegmentedList<string>
         }
     }
 
+    private Build.Framework.ILogger? CreateMSBuildLogger()
+    {
+        if (_globalOptionService.GetOption(LanguageServerProjectSystemOptionsStorage.BinaryLogPath) is not string binaryLogDirectory)
+            return null;
+
+        var numericSuffix = Interlocked.Increment(ref _binaryLogNumericSuffix);
+        var binaryLogPath = Path.Combine(binaryLogDirectory, $"LanguageServerDesignTimeBuild-{_binaryLogGuidSuffix}-{numericSuffix}.binlog");
+
+        _logger.LogInformation($"Logging design-time builds to {binaryLogPath}");
+
+        return new BinaryLogger { Parameters = binaryLogPath, Verbosity = Build.Framework.LoggerVerbosity.Diagnostic };
+    }
+
     private async Task<LSP.MessageType?> LoadOrReloadProjectAsync(string projectPath, ProjectBuildManager projectBuildManager, CancellationToken cancellationToken)
     {
         try

src/Features/LanguageServer/Protocol/Features/Options/LanguageServerProjectSystemOptionsStorage.cs

@@ -0,0 +1,18 @@
+// 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 Microsoft.CodeAnalysis.Options;
+
+namespace Microsoft.CodeAnalysis.LanguageServer.HostWorkspace
+{
+    internal static class LanguageServerProjectSystemOptionsStorage
+    {
+        private static readonly OptionGroup s_optionGroup = new(name: "project_loading", description: "");
+
+        /// <summary>
+        /// A folder to log binlogs to when running design-time builds.
+        /// </summary>
+        public static readonly Option2<string?> BinaryLogPath = new Option2<string?>("dotnet_binary_log_path", defaultValue: null, s_optionGroup);
+    }
+}

src/Features/LanguageServer/Protocol/Handler/Configuration/DidChangeConfigurationNotificationHandler_OptionList.cs

@@ -8,6 +8,7 @@
 using Microsoft.CodeAnalysis.Formatting;
 using Microsoft.CodeAnalysis.ImplementType;
 using Microsoft.CodeAnalysis.InlineHints;
+using Microsoft.CodeAnalysis.LanguageServer.HostWorkspace;
 using Microsoft.CodeAnalysis.MetadataAsSource;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.QuickInfo;
@@ -58,6 +59,8 @@ internal partial class DidChangeConfigurationNotificationHandler
             SolutionCrawlerOptionsStorage.CompilerDiagnosticsScopeOption,
             // Code lens options
             LspOptionsStorage.LspEnableReferencesCodeLens,
-            LspOptionsStorage.LspEnableTestsCodeLens);
+            LspOptionsStorage.LspEnableTestsCodeLens,
+            // Project system
+            LanguageServerProjectSystemOptionsStorage.BinaryLogPath);
     }
 }