Add an LSP notification for loading projects

This is the server side portion of
dotnet/vscode-csharp#6062

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

@@ -7,19 +7,16 @@
 using System.Composition;
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
-using System.Threading;
 using Microsoft.Build.Locator;
 using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.MSBuild;
 using Microsoft.CodeAnalysis.MSBuild.Build;
-using Microsoft.CodeAnalysis.MSBuild.Logging;
 using Microsoft.CodeAnalysis.ProjectSystem;
 using Microsoft.CodeAnalysis.Shared.TestHooks;
 using Microsoft.CodeAnalysis.Workspaces.ProjectSystem;
 using Microsoft.Extensions.Logging;
 using Microsoft.VisualStudio.Composition;
-using Microsoft.VisualStudio.TestPlatform.CommunicationUtilities;
 using Roslyn.Utilities;
 using LSP = Microsoft.VisualStudio.LanguageServer.Protocol;
 
@@ -77,14 +74,8 @@ public LanguageServerProjectSystem(
 
     public async Task OpenSolutionAsync(string solutionFilePath)
     {
-        var result = await TryEnsureMSBuildLoadedAsync(Path.GetDirectoryName(solutionFilePath)!);
-        if (!result)
-        {
-            var message = string.Format(LanguageServerResources.There_were_errors_loading_solution_0_See_log_for_details, Path.GetFileName(solutionFilePath));
-            await ShowToastNotification.ShowToastNotificationAsync(LSP.MessageType.Error, message, CancellationToken.None, ShowToastNotification.ShowCSharpLogsCommand);
-        }
-
-        await OpenSolutionCoreAsync(solutionFilePath);
+        if (await TryEnsureMSBuildLoadedAsync(Path.GetDirectoryName(solutionFilePath)!))
+            await OpenSolutionCoreAsync(solutionFilePath);
     }
 
     [MethodImpl(MethodImplOptions.NoInlining)] // Don't inline; the caller needs to ensure MSBuild is loaded before we can use MSBuild types here
@@ -112,6 +103,28 @@ private async Task OpenSolutionCoreAsync(string solutionFilePath)
         }
     }
 
+    public async Task OpenProjectsAsync(ImmutableArray<string> projectFilePaths)
+    {
+        if (!projectFilePaths.Any())
+            return;
+
+        if (await TryEnsureMSBuildLoadedAsync(Path.GetDirectoryName(projectFilePaths.First())!))
+            await OpenProjectsCoreAsync(projectFilePaths);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)] // Don't inline; the caller needs to ensure MSBuild is loaded before we can use MSBuild types here
+    private async Task OpenProjectsCoreAsync(ImmutableArray<string> projectFilePaths)
+    {
+        using (await _gate.DisposableWaitAsync())
+        {
+            _projectsToLoadAndReload.AddWork(projectFilePaths);
+
+            // Wait for the in progress batch to complete and send a project initialized notification to the client.
+            await _projectsToLoadAndReload.WaitUntilCurrentBatchCompletesAsync();
+            await ProjectInitializationHandler.SendProjectInitializationCompleteNotificationAsync();
+        }
+    }
+
     private async Task<bool> TryEnsureMSBuildLoadedAsync(string workingDirectory)
     {
         using (await _gate.DisposableWaitAsync())
@@ -137,6 +150,8 @@ private async Task<bool> TryEnsureMSBuildLoadedAsync(string workingDirectory)
                 else
                 {
                     _logger.LogError($"Unable to find a MSBuild to use to load {workingDirectory}.");
+                    await ShowToastNotification.ShowToastNotificationAsync(LSP.MessageType.Error, LanguageServerResources.There_were_problems_loading_your_projects_See_log_for_details, CancellationToken.None, ShowToastNotification.ShowCSharpLogsCommand);
+
                     return false;
                 }
             }

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

@@ -0,0 +1,41 @@
+// 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.Composition;
+using System.Runtime.Serialization;
+using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.LanguageServer.Handler;
+using Microsoft.CommonLanguageServerProtocol.Framework;
+using Roslyn.Utilities;
+
+namespace Microsoft.CodeAnalysis.LanguageServer.HostWorkspace;
+
+[ExportCSharpVisualBasicStatelessLspService(typeof(OpenProjectHandler)), Shared]
+[Method("project/open")]
+internal class OpenProjectHandler : ILspServiceNotificationHandler<OpenProjectHandler.NotificationParams>
+{
+    private readonly LanguageServerProjectSystem _projectSystem;
+
+    [ImportingConstructor]
+    [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
+    public OpenProjectHandler(LanguageServerProjectSystem projectSystem)
+    {
+        _projectSystem = projectSystem;
+    }
+
+    public bool MutatesSolutionState => false;
+    public bool RequiresLSPSolution => false;
+
+    Task INotificationHandler<NotificationParams, RequestContext>.HandleNotificationAsync(NotificationParams request, RequestContext requestContext, CancellationToken cancellationToken)
+    {
+        return _projectSystem.OpenProjectsAsync(request.Projects.SelectAsArray(p => p.LocalPath));
+    }
+
+    [DataContract]
+    private class NotificationParams
+    {
+        [DataMember(Name = "projects")]
+        public required Uri[] Projects { get; set; }
+    }
+}

src/Features/LanguageServer/Microsoft.CodeAnalysis.LanguageServer/LanguageServerResources.resx

@@ -189,6 +189,9 @@
   <data name="There_were_errors_loading_solution_0_See_log_for_details" xml:space="preserve">
     <value>There were errors loading solutution {0}. See log for details.</value>
   </data>
+  <data name="There_were_problems_loading_your_projects_See_log_for_details" xml:space="preserve">
+    <value>There were problems loading your projects. See log for details.</value>
+  </data>
   <data name="There_were_warnings_loading_project_0_See_log_for_details" xml:space="preserve">
     <value>There were warnings loading project {0}. See log for details.</value>
   </data>