Document diagnostics supersede workspace diagnostics

src/Features/LanguageServer/Protocol/Handler/Diagnostics/AbstractPullDiagnosticHandler.cs

@@ -24,6 +24,13 @@ namespace Microsoft.CodeAnalysis.LanguageServer.Handler.Diagnostics
     internal abstract class AbstractPullDiagnosticHandler<TDiagnosticsParams, TReport> : IRequestHandler<TDiagnosticsParams, TReport[]?>
         where TReport : DiagnosticReport
     {
+        /// <summary>
+        /// Special value we use to designate workspace diagnostics vs document diagnostics.  Document diagnostics
+        /// should always <see cref="DiagnosticReport.Supersedes"/> a workspace diagnostic as the former are 'live'
+        /// while the latter are cached and may be stale.
+        /// </summary>
+        protected const int WorkspaceDiagnosticIdentifier = 1;
+
         protected readonly IDiagnosticService DiagnosticService;
 
         /// <summary>
@@ -78,6 +85,11 @@ internal abstract class AbstractPullDiagnosticHandler<TDiagnosticsParams, TRepor
         /// </summary>
         protected abstract Task<ImmutableArray<DiagnosticData>> GetDiagnosticsAsync(RequestContext context, Document document, Option2<DiagnosticMode> diagnosticMode, CancellationToken cancellationToken);
 
+        /// <summary>
+        /// Generate the right diagnostic tags for a particular diagnostic.
+        /// </summary>
+        protected abstract DiagnosticTag[] ConvertTags(DiagnosticData diagnosticData);
+
         private void OnDiagnosticsUpdated(object? sender, DiagnosticsUpdatedArgs updateArgs)
         {
             if (updateArgs.DocumentId == null)
@@ -290,7 +302,7 @@ private static LSP.DiagnosticSeverity ConvertDiagnosticSeverity(DiagnosticSeveri
         /// If you make change in this method, please also update the corresponding file in
         /// src\VisualStudio\Xaml\Impl\Implementation\LanguageServer\Handler\Diagnostics\AbstractPullDiagnosticHandler.cs
         /// </summary>
-        private static DiagnosticTag[] ConvertTags(DiagnosticData diagnosticData)
+        protected DiagnosticTag[] ConvertTags(DiagnosticData diagnosticData, bool potentialDuplicate)
         {
             using var _ = ArrayBuilder<DiagnosticTag>.GetInstance(out var result);
 
@@ -305,6 +317,9 @@ private static DiagnosticTag[] ConvertTags(DiagnosticData diagnosticData)
                 result.Add(VSDiagnosticTags.VisibleInErrorList);
             }
 
+            if (potentialDuplicate)
+                result.Add(VSDiagnosticTags.PotentialDuplicate);
+
             result.Add(diagnosticData.CustomTags.Contains(WellKnownDiagnosticTags.Build)
                 ? VSDiagnosticTags.BuildError
                 : VSDiagnosticTags.IntellisenseError);

src/Features/LanguageServer/Protocol/Handler/Diagnostics/DocumentPullDiagnosticHandler.cs

@@ -10,7 +10,6 @@
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.Options;
-using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 using Roslyn.Utilities;
 
@@ -35,14 +34,26 @@ internal class DocumentPullDiagnosticHandler : AbstractPullDiagnosticHandler<Doc
             => diagnosticsParams.TextDocument;
 
         protected override DiagnosticReport CreateReport(TextDocumentIdentifier? identifier, VSDiagnostic[]? diagnostics, string? resultId)
-            => new DiagnosticReport { Diagnostics = diagnostics, ResultId = resultId };
+            => new DiagnosticReport
+            {
+                Diagnostics = diagnostics,
+                ResultId = resultId,
+                // Mark these diagnostics as superseding any diagnostics for the same document from the
+                // WorkspacePullDiagnosticHandler. We are always getting completely accurate and up to date diagnostic
+                // values for a particular file, so our results should always be preferred over the workspace-pull
+                // values which are cached and may be out of date.
+                Supersedes = WorkspaceDiagnosticIdentifier,
+            };
 
         protected override DiagnosticParams[]? GetPreviousResults(DocumentDiagnosticsParams diagnosticsParams)
             => new[] { diagnosticsParams };
 
         protected override IProgress<DiagnosticReport[]>? GetProgress(DocumentDiagnosticsParams diagnosticsParams)
             => diagnosticsParams.PartialResultToken;
 
+        protected override DiagnosticTag[] ConvertTags(DiagnosticData diagnosticData)
+            => ConvertTags(diagnosticData, potentialDuplicate: false);
+
         protected override ImmutableArray<Document> GetOrderedDocuments(RequestContext context)
         {
             // For the single document case, that is the only doc we want to process.

src/Features/LanguageServer/Protocol/Handler/Diagnostics/WorkspacePullDiagnosticHandler.cs

@@ -31,14 +31,29 @@ public WorkspacePullDiagnosticHandler(IDiagnosticService diagnosticService)
             => null;
 
         protected override WorkspaceDiagnosticReport CreateReport(TextDocumentIdentifier? identifier, VSDiagnostic[]? diagnostics, string? resultId)
-            => new WorkspaceDiagnosticReport { TextDocument = identifier, Diagnostics = diagnostics, ResultId = resultId };
+            => new WorkspaceDiagnosticReport
+            {
+                TextDocument = identifier,
+                Diagnostics = diagnostics,
+                ResultId = resultId,
+                // Mark these diagnostics as having come from us.  They will be superseded by any diagnostics for the
+                // same file produced by the DocumentPullDiagnosticHandler.
+                Identifier = WorkspaceDiagnosticIdentifier,
+            };
 
         protected override IProgress<WorkspaceDiagnosticReport[]>? GetProgress(WorkspaceDocumentDiagnosticsParams diagnosticsParams)
             => diagnosticsParams.PartialResultToken;
 
         protected override DiagnosticParams[]? GetPreviousResults(WorkspaceDocumentDiagnosticsParams diagnosticsParams)
             => diagnosticsParams.PreviousResults;
 
+        protected override DiagnosticTag[] ConvertTags(DiagnosticData diagnosticData)
+        {
+            // All workspace diagnostics are potential duplicates given that they can be overridden by the diagnostics
+            // produced by document diagnostics.
+            return ConvertTags(diagnosticData, potentialDuplicate: true);
+        }
+
         protected override ImmutableArray<Document> GetOrderedDocuments(RequestContext context)
         {
             // If we're being called from razor, we do not support WorkspaceDiagnostics at all.  For razor, workspace