Don't compute the information for the code definition window if not open

src/EditorFeatures/Core/Implementation/CodeDefinitionWindow/DefinitionContextTracker.cs

@@ -124,6 +124,14 @@ private async Task UpdateForCaretPositionAsync(SnapshotPoint pointInRoslynSnapsh
             {
                 await _asyncListener.Delay(TimeSpan.FromMilliseconds(250), cancellationToken).ConfigureAwait(false);
 
+                // If it's not open, don't do anything, since if we are going to show locations in metadata that might
+                // be expensive. This doesn't cause a functional issue, since opening the window clears whatever was previously there
+                // so the user won't notice we weren't doing anything when it was open.
+                if (!await _codeDefinitionWindowService.IsWindowOpenAsync(cancellationToken).ConfigureAwait(false))
+                {
+                    return;
+                }
+
                 var document = pointInRoslynSnapshot.Snapshot.GetOpenDocumentInCurrentContextWithChanges();
                 if (document == null)
                 {

src/EditorFeatures/Core/Implementation/CodeDefinitionWindow/ICodeDefinitionWindowService.cs

@@ -10,6 +10,7 @@ namespace Microsoft.CodeAnalysis.Editor.Implementation.CodeDefinitionWindow
 {
     internal interface ICodeDefinitionWindowService
     {
+        Task<bool> IsWindowOpenAsync(CancellationToken cancellationToken);
         Task SetContextAsync(ImmutableArray<CodeDefinitionWindowLocation> locations, CancellationToken cancellationToken);
     }
 }

src/EditorFeatures/Test2/CodeDefinitionWindow/AbstractCodeDefinitionWindowTests.vb

@@ -30,6 +30,10 @@ Namespace Microsoft.CodeAnalysis.Editor.CodeDefinitionWindow.UnitTests
             Public Sub New()
             End Sub
 
+            Public Function IsWindowOpenAsync(cancellationToken As CancellationToken) As Task(Of Boolean) Implements ICodeDefinitionWindowService.IsWindowOpenAsync
+                Throw New NotImplementedException()
+            End Function
+
             Public Function SetContextAsync(locations As ImmutableArray(Of CodeDefinitionWindowLocation), cancellationToken As CancellationToken) As Task Implements ICodeDefinitionWindowService.SetContextAsync
                 Throw New NotImplementedException()
             End Function

src/VisualStudio/Core/Def/Implementation/CodeDefinitionWindow/VisualStudioCodeDefinitionWindowService.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Immutable;
 using System.Composition;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Threading;
@@ -23,6 +24,9 @@ internal sealed class VisualStudioCodeDefinitionWindowService : ICodeDefinitionW
         private readonly IAsyncServiceProvider _asyncServiceProvider;
         private readonly IThreadingContext _threadingContext;
 
+        [DisallowNull]
+        private IVsCodeDefView? _lazyCodeDefView;
+
         [ImportingConstructor]
         [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
         public VisualStudioCodeDefinitionWindowService(SVsServiceProvider asyncServiceProvider, IThreadingContext threadingContext)
@@ -31,6 +35,29 @@ public VisualStudioCodeDefinitionWindowService(SVsServiceProvider asyncServicePr
             _threadingContext = threadingContext;
         }
 
+        private async Task<IVsCodeDefView> GetVsCodeDefViewAsync()
+        {
+            if (_lazyCodeDefView is not null)
+            {
+                return _lazyCodeDefView;
+            }
+
+            _lazyCodeDefView = await _asyncServiceProvider.GetServiceAsync<SVsCodeDefView, IVsCodeDefView>().ConfigureAwait(true);
+
+            return _lazyCodeDefView;
+        }
+
+        public async Task<bool> IsWindowOpenAsync(CancellationToken cancellationToken)
+        {
+            var vsCodeDefView = await GetVsCodeDefViewAsync().ConfigureAwait(true);
+
+            // Switch to the UI thread before using the IVsCodeDefView service
+            await _threadingContext.JoinableTaskFactory.SwitchToMainThreadAsync(cancellationToken);
+
+            // IsVisible returns S_FALSE if it's not visible
+            return vsCodeDefView.IsVisible() == VSConstants.S_OK;
+        }
+
         public async Task SetContextAsync(ImmutableArray<CodeDefinitionWindowLocation> locations, CancellationToken cancellationToken)
         {
             // If the new context has no location, then just don't update, instead of showing the
@@ -40,7 +67,7 @@ public async Task SetContextAsync(ImmutableArray<CodeDefinitionWindowLocation> l
                 return;
             }
 
-            var vsCodeDefView = await _asyncServiceProvider.GetServiceAsync<SVsCodeDefView, IVsCodeDefView>().ConfigureAwait(false);
+            var vsCodeDefView = await GetVsCodeDefViewAsync().ConfigureAwait(true);
 
             // Switch to the UI thread before using the IVsCodeDefView service
             await _threadingContext.JoinableTaskFactory.SwitchToMainThreadAsync(cancellationToken);