Allow access to Roslyn diagnostics from Razor

src/Tools/ExternalAccess/Razor/Cohost/Handlers/Diagnostics.cs

@@ -0,0 +1,39 @@
+// 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.Collections.Immutable;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.LanguageServer;
+using Microsoft.CodeAnalysis.Options;
+using Microsoft.CodeAnalysis.PooledObjects;
+using LSP = Roslyn.LanguageServer.Protocol;
+
+namespace Microsoft.CodeAnalysis.ExternalAccess.Razor.Cohost.Handlers;
+
+internal static class Diagnostics
+{
+    public static async Task<ImmutableArray<LSP.Diagnostic>> GetDocumentDiagnosticsAsync(Document document, bool supportsVisualStudioExtensions, CancellationToken cancellationToken)
+    {
+        var globalOptionsService = document.Project.Solution.Services.ExportProvider.GetService<IGlobalOptionService>();
+        var diagnosticAnalyzerService = document.Project.Solution.Services.ExportProvider.GetService<IDiagnosticAnalyzerService>();
+
+        var diagnostics = await diagnosticAnalyzerService.GetDiagnosticsForSpanAsync(document, range: null, cancellationToken).ConfigureAwait(false);
+
+        var project = document.Project;
+        // isLiveSource means build might override a diagnostics, but this method is only used by tooling, so builds aren't relevant
+        const bool IsLiveSource = false;
+        // Potential duplicate is only set for workspace diagnostics
+        const bool PotentialDuplicate = false;
+
+        var result = ArrayBuilder<LSP.Diagnostic>.GetInstance(capacity: diagnostics.Length);
+        foreach (var diagnostic in diagnostics)
+        {
+            result.AddRange(ProtocolConversions.ConvertDiagnostic(diagnostic, supportsVisualStudioExtensions, project, IsLiveSource, PotentialDuplicate, globalOptionsService));
+        }
+
+        return result.ToImmutableAndFree();
+    }
+}