Avoid Task allocations in common document extensions

src/CodeStyle/Core/CodeFixes/LanguageServices/SemanticModelWorkspaceService/SemanticModelWorkspaceServiceFactory.SemanticModelWorkspaceService.cs

@@ -17,7 +17,7 @@ public SemanticModelReuseWorkspaceService(Workspace _)
             {
             }
 
-            public Task<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken)
+            public ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken)
             {
                 // TODO: port the GetSemanticModelForNodeAsync implementation from Workspaces layer,
                 // which currently relies on a bunch of internal APIs.

src/EditorFeatures/TestUtilities/ChangeSignature/AddedParameterOrExistingIndex.cs

@@ -61,7 +61,7 @@ public override string ToString()
 
         internal AddedParameter GetAddedParameter(Document document)
         {
-            var semanticModel = document.GetRequiredSemanticModelAsync(CancellationToken.None).Result;
+            var semanticModel = document.GetRequiredSemanticModelAsync(CancellationToken.None).AsTask().Result;
 
             var type = document.Project.Language switch
             {

src/VisualStudio/Core/Def/Implementation/AbstractEditorFactory.cs

@@ -321,7 +321,7 @@ private void FormatDocumentCreatedFromTemplate(IVsHierarchy hierarchy, uint item
 
             // Organize using directives
             addedDocument = ThreadHelper.JoinableTaskFactory.Run(() => OrganizeUsingsCreatedFromTemplateAsync(addedDocument, cancellationToken));
-            rootToFormat = ThreadHelper.JoinableTaskFactory.Run(() => addedDocument.GetRequiredSyntaxRootAsync(cancellationToken));
+            rootToFormat = ThreadHelper.JoinableTaskFactory.Run(() => addedDocument.GetRequiredSyntaxRootAsync(cancellationToken).AsTask());
 
             // Format document
             var unformattedText = addedDocument.GetTextSynchronously(cancellationToken);

src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialogViewModel.cs

@@ -27,7 +27,7 @@ internal class AddParameterDialogViewModel : AbstractNotifyPropertyChanged
         public AddParameterDialogViewModel(Document document, int positionForTypeBinding)
         {
             _notificationService = document.Project.Solution.Workspace.Services.GetService<INotificationService>();
-            _semanticModel = document.GetRequiredSemanticModelAsync(CancellationToken.None).WaitAndGetResult_CanCallOnBackground(CancellationToken.None);
+            _semanticModel = document.GetRequiredSemanticModelAsync(CancellationToken.None).AsTask().WaitAndGetResult_CanCallOnBackground(CancellationToken.None);
 
             TypeIsEmptyImage = Visibility.Visible;
             TypeBindsImage = Visibility.Collapsed;

src/Workspaces/Core/Portable/ExternalAccess/Pythia/Api/PythiaDocumentExtensions.cs

@@ -11,6 +11,6 @@ namespace Microsoft.CodeAnalysis.ExternalAccess.Pythia.Api
     internal static class PythiaDocumentExtensions
     {
         public static Task<SemanticModel> GetSemanticModelForNodeAsync(this Document document, SyntaxNode? node, CancellationToken cancellationToken)
-            => DocumentExtensions.ReuseExistingSpeculativeModelAsync(document, node, cancellationToken);
+            => DocumentExtensions.ReuseExistingSpeculativeModelAsync(document, node, cancellationToken).AsTask();
     }
 }

src/Workspaces/Core/Portable/SemanticModelReuse/SemanticModelWorkspaceServiceFactory.SemanticModelWorkspaceService.cs

@@ -90,7 +90,7 @@ public SemanticModelReuseWorkspaceService(Workspace workspace)
                 };
             }
 
-            public async Task<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken)
+            public async ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken)
             {
                 var reuseService = document.GetRequiredLanguageService<ISemanticModelReuseLanguageService>();
 

src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Extensions/DocumentExtensions.cs

@@ -9,7 +9,6 @@
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.GeneratedCodeRecognition;
 using Microsoft.CodeAnalysis.Host;
-using Microsoft.CodeAnalysis.LanguageServices;
 using Microsoft.CodeAnalysis.SemanticModelReuse;
 using Microsoft.CodeAnalysis.Text;
 using Roslyn.Utilities;
@@ -30,15 +29,21 @@ internal static partial class DocumentExtensions
         public static TLanguageService GetRequiredLanguageService<TLanguageService>(this Document document) where TLanguageService : class, ILanguageService
             => document.Project.GetRequiredLanguageService<TLanguageService>();
 
-        public static async Task<SemanticModel> GetRequiredSemanticModelAsync(this Document document, CancellationToken cancellationToken)
+        public static async ValueTask<SemanticModel> GetRequiredSemanticModelAsync(this Document document, CancellationToken cancellationToken)
         {
-            var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            if (document.TryGetSemanticModel(out var semanticModel))
+                return semanticModel;
+
+            semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
             return semanticModel ?? throw new InvalidOperationException(string.Format(WorkspaceExtensionsResources.SyntaxTree_is_required_to_accomplish_the_task_but_is_not_supported_by_document_0, document.Name));
         }
 
-        public static async Task<SyntaxTree> GetRequiredSyntaxTreeAsync(this Document document, CancellationToken cancellationToken)
+        public static async ValueTask<SyntaxTree> GetRequiredSyntaxTreeAsync(this Document document, CancellationToken cancellationToken)
         {
-            var syntaxTree = await document.GetSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
+            if (document.TryGetSyntaxTree(out var syntaxTree))
+                return syntaxTree;
+
+            syntaxTree = await document.GetSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
             return syntaxTree ?? throw new InvalidOperationException(string.Format(WorkspaceExtensionsResources.SyntaxTree_is_required_to_accomplish_the_task_but_is_not_supported_by_document_0, document.Name));
         }
 
@@ -50,9 +55,12 @@ public static SyntaxTree GetRequiredSyntaxTreeSynchronously(this Document docume
         }
 #endif
 
-        public static async Task<SyntaxNode> GetRequiredSyntaxRootAsync(this Document document, CancellationToken cancellationToken)
+        public static async ValueTask<SyntaxNode> GetRequiredSyntaxRootAsync(this Document document, CancellationToken cancellationToken)
         {
-            var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            if (document.TryGetSyntaxRoot(out var root))
+                return root;
+
+            root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
             return root ?? throw new InvalidOperationException(string.Format(WorkspaceExtensionsResources.SyntaxTree_is_required_to_accomplish_the_task_but_is_not_supported_by_document_0, document.Name));
         }
 
@@ -76,7 +84,7 @@ public static bool IsOpen(this TextDocument document)
         /// <para/>
         /// As a speculative semantic model may be returned, location based information provided by it may be innacurate.
         /// </summary>
-        public static Task<SemanticModel> ReuseExistingSpeculativeModelAsync(this Document document, int position, CancellationToken cancellationToken)
+        public static ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(this Document document, int position, CancellationToken cancellationToken)
             => ReuseExistingSpeculativeModelAsync(document, new TextSpan(position, 0), cancellationToken);
 
         /// <summary>
@@ -93,7 +101,7 @@ public static Task<SemanticModel> ReuseExistingSpeculativeModelAsync(this Docume
         /// <para/>
         /// As a speculative semantic model may be returned, location based information provided by it may be innacurate.
         /// </summary>
-        public static async Task<SemanticModel> ReuseExistingSpeculativeModelAsync(this Document document, TextSpan span, CancellationToken cancellationToken)
+        public static async ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(this Document document, TextSpan span, CancellationToken cancellationToken)
         {
             Contract.ThrowIfFalse(document.SupportsSemanticModel);
 
@@ -118,7 +126,7 @@ public static async Task<SemanticModel> ReuseExistingSpeculativeModelAsync(this
         /// <para/>
         /// As a speculative semantic model may be returned, location based information provided by it may be innacurate.
         /// </summary>
-        public static Task<SemanticModel> ReuseExistingSpeculativeModelAsync(this Document document, SyntaxNode? node, CancellationToken cancellationToken)
+        public static ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(this Document document, SyntaxNode? node, CancellationToken cancellationToken)
         {
             if (node == null)
                 return document.GetRequiredSemanticModelAsync(cancellationToken);

src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/WorkspaceServices/SemanticModelReuse/ISemanticModelReuseWorkspaceService.cs

@@ -18,6 +18,6 @@ internal interface ISemanticModelReuseWorkspaceService : IWorkspaceService
         /// <summary>
         /// Don't call this directly. use <see cref="DocumentExtensions.ReuseExistingSpeculativeModelAsync(Document, SyntaxNode, CancellationToken)"/> (or an overload).
         /// </summary>
-        Task<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken);
+        ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken);
     }
 }