Merge pull request #9194 from DustinCampbell/completion-cleanup

Clean up completion to return ImmutableArray<T> rather than IReadOnlyList<T>

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/DirectiveAttributeTransitionCompletionItemProvider.cs

@@ -2,7 +2,7 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
+using System.Collections.Immutable;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
 using Microsoft.AspNetCore.Razor.LanguageServer.Extensions;
@@ -39,9 +39,9 @@ internal class DirectiveAttributeTransitionCompletionItemProvider : DirectiveAtt
         }
     }
 
-    private static readonly IReadOnlyList<RazorCompletionItem> s_completions = new[] { TransitionCompletionItem };
+    private static readonly ImmutableArray<RazorCompletionItem> s_completions = ImmutableArray.Create(TransitionCompletionItem);
 
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    public override ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
         if (context is null)
         {
@@ -51,13 +51,13 @@ internal class DirectiveAttributeTransitionCompletionItemProvider : DirectiveAtt
         if (!FileKinds.IsComponent(context.SyntaxTree.Options.FileKind))
         {
             // Directive attributes are only supported in components
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         var owner = context.Owner;
         if (owner is null)
         {
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         var attribute = owner.Parent;
@@ -69,19 +69,19 @@ internal class DirectiveAttributeTransitionCompletionItemProvider : DirectiveAtt
 
         if (!TryGetAttributeInfo(owner, out var prefixLocation, out var attributeName, out var attributeNameLocation, out _, out _))
         {
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (attributeNameLocation.IntersectsWith(context.AbsoluteIndex) && attributeName.StartsWith("@", StringComparison.Ordinal))
         {
             // The transition is already provided for the attribute name
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!IsValidCompletionPoint(context.AbsoluteIndex, prefixLocation, attributeNameLocation))
         {
             // Not operating in the attribute name area
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         // This represents a tag when there's no attribute content <InputText | />.

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/LegacyRazorCompletionEndpoint.cs

@@ -2,7 +2,7 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
@@ -12,6 +12,7 @@ using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Microsoft.AspNetCore.Razor.LanguageServer.EndpointContracts;
 using Microsoft.AspNetCore.Razor.LanguageServer.Extensions;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor.Completion;
 using Microsoft.Extensions.Logging;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
@@ -23,7 +24,7 @@ namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion;
 // for this legacy version.
 internal class LegacyRazorCompletionEndpoint : IVSCompletionEndpoint
 {
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
     private readonly CompletionListCache _completionListCache;
     private static readonly Command s_retriggerCompletionCommand = new()
     {
@@ -34,22 +35,10 @@ internal class LegacyRazorCompletionEndpoint : IVSCompletionEndpoint
 
     public bool MutatesSolutionState => false;
 
-    public LegacyRazorCompletionEndpoint(
+    public LegacyRazorCompletionEndpoint(IRazorCompletionFactsService completionFactsService, CompletionListCache completionListCache)
-        RazorCompletionFactsService completionFactsService,
-        CompletionListCache completionListCache)
     {
-        if (completionFactsService is null)
+        _completionFactsService = completionFactsService ?? throw new ArgumentNullException(nameof(completionFactsService));
-        {
+        _completionListCache = completionListCache ?? throw new ArgumentNullException(nameof(completionListCache));
-            throw new ArgumentNullException(nameof(completionFactsService));
-        }
-
-        if (completionListCache is null)
-        {
-            throw new ArgumentNullException(nameof(completionListCache));
-        }
-
-        _completionFactsService = completionFactsService;
-        _completionListCache = completionListCache;
     }
 
     public void ApplyCapabilities(VSInternalServerCapabilities serverCapabilities, VSInternalClientCapabilities clientCapabilities)
@@ -107,7 +96,7 @@ internal class LegacyRazorCompletionEndpoint : IVSCompletionEndpoint
 
         var razorCompletionItems = _completionFactsService.GetCompletionItems(completionContext);
 
-        requestContext.Logger.LogTrace("Resolved {razorCompletionItemsCount} completion items.", razorCompletionItems.Count);
+        requestContext.Logger.LogTrace("Resolved {razorCompletionItemsCount} completion items.", razorCompletionItems.Length);
 
         var completionList = CreateLSPCompletionList(razorCompletionItems);
         var completionCapability = _clientCapabilities?.TextDocument?.Completion as VSInternalCompletionSetting;
@@ -140,31 +129,33 @@ internal class LegacyRazorCompletionEndpoint : IVSCompletionEndpoint
     }
 
     // Internal for testing
-    internal VSInternalCompletionList CreateLSPCompletionList(IReadOnlyList<RazorCompletionItem> razorCompletionItems) => CreateLSPCompletionList(razorCompletionItems, _clientCapabilities!);
+    internal VSInternalCompletionList CreateLSPCompletionList(ImmutableArray<RazorCompletionItem> razorCompletionItems)
+        => CreateLSPCompletionList(razorCompletionItems, _clientCapabilities!);
 
     // Internal for benchmarking and testing
     internal static VSInternalCompletionList CreateLSPCompletionList(
-        IReadOnlyList<RazorCompletionItem> razorCompletionItems,
+        ImmutableArray<RazorCompletionItem> razorCompletionItems,
         VSInternalClientCapabilities clientCapabilities)
     {
-        var completionItems = new List<CompletionItem>();
+        using var items = new PooledArrayBuilder<CompletionItem>();
+
         foreach (var razorCompletionItem in razorCompletionItems)
         {
             if (TryConvert(razorCompletionItem, clientCapabilities, out var completionItem))
             {
-                completionItems.Add(completionItem);
+                items.Add(completionItem);
             }
         }
 
         var completionList = new VSInternalCompletionList()
         {
-            Items = completionItems.ToArray(),
+            Items = items.ToArray(),
             IsIncomplete = false,
         };
 
         var completionCapability = clientCapabilities?.TextDocument?.Completion as VSInternalCompletionSetting;
-        var optimizedCompletionList = CompletionListOptimizer.Optimize(completionList, completionCapability);
+
-        return optimizedCompletionList;
+        return CompletionListOptimizer.Optimize(completionList, completionCapability);
     }
 
     // Internal for testing

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/RazorCompletionListProvider.cs

@@ -12,6 +12,7 @@ using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Microsoft.AspNetCore.Razor.LanguageServer.Extensions;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor.Completion;
 using Microsoft.Extensions.Logging;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
@@ -20,7 +21,7 @@ namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion;
 
 internal class RazorCompletionListProvider
 {
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
     private readonly CompletionListCache _completionListCache;
     private readonly ILogger<RazorCompletionListProvider> _logger;
     private static readonly Command s_retriggerCompletionCommand = new()
@@ -30,7 +31,7 @@ internal class RazorCompletionListProvider
     };
 
     public RazorCompletionListProvider(
-        RazorCompletionFactsService completionFactsService,
+        IRazorCompletionFactsService completionFactsService,
         CompletionListCache completionListCache,
         ILoggerFactory loggerFactory)
     {
@@ -63,6 +64,7 @@ internal class RazorCompletionListProvider
             CompletionTriggerKind.TriggerCharacter => CompletionReason.Typing,
             _ => CompletionReason.Typing,
         };
+
         var completionOptions = new RazorCompletionOptions(SnippetsSupported: true);
         var syntaxTree = await documentContext.GetSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
         var tagHelperContext = await documentContext.GetTagHelperContextAsync(cancellationToken).ConfigureAwait(false);
@@ -79,7 +81,7 @@ internal class RazorCompletionListProvider
 
         var razorCompletionItems = _completionFactsService.GetCompletionItems(razorCompletionContext);
 
-        _logger.LogTrace("Resolved {razorCompletionItemsCount} completion items.", razorCompletionItems.Count);
+        _logger.LogTrace("Resolved {razorCompletionItemsCount} completion items.", razorCompletionItems.Length);
 
         var completionList = CreateLSPCompletionList(razorCompletionItems, clientCapabilities);
 
@@ -94,27 +96,28 @@ internal class RazorCompletionListProvider
 
     // Internal for benchmarking and testing
     internal static VSInternalCompletionList CreateLSPCompletionList(
-        IReadOnlyList<RazorCompletionItem> razorCompletionItems,
+        ImmutableArray<RazorCompletionItem> razorCompletionItems,
         VSInternalClientCapabilities clientCapabilities)
     {
-        var completionItems = new List<CompletionItem>();
+        using var items = new PooledArrayBuilder<CompletionItem>();
+
         foreach (var razorCompletionItem in razorCompletionItems)
         {
             if (TryConvert(razorCompletionItem, clientCapabilities, out var completionItem))
             {
-                completionItems.Add(completionItem);
+                items.Add(completionItem);
             }
         }
 
         var completionList = new VSInternalCompletionList()
         {
-            Items = completionItems.ToArray(),
+            Items = items.ToArray(),
             IsIncomplete = false,
         };
 
         var completionCapability = clientCapabilities.TextDocument?.Completion as VSInternalCompletionSetting;
-        var optimizedCompletionList = CompletionListOptimizer.Optimize(completionList, completionCapability);
+
-        return optimizedCompletionList;
+        return CompletionListOptimizer.Optimize(completionList, completionCapability);
     }
 
     // Internal for testing

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Completion/TagHelperCompletionProvider.cs

@@ -3,11 +3,13 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor.Completion;
 using Microsoft.CodeAnalysis.Razor.Tooltip;
 using Microsoft.Extensions.Options;
@@ -15,7 +17,7 @@ using Microsoft.VisualStudio.Editor.Razor;
 
 namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion;
 
-internal class TagHelperCompletionProvider : RazorCompletionItemProvider
+internal class TagHelperCompletionProvider : IRazorCompletionItemProvider
 {
     // Internal for testing
     internal static readonly IReadOnlyList<RazorCommitCharacter> MinimizedAttributeCommitCharacters = RazorCommitCharacter.FromArray(new[] { "=", " " });
@@ -41,7 +43,7 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
         _optionsMonitor = optionsMonitor ?? throw new ArgumentNullException(nameof(optionsMonitor));
     }
 
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    public ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
         if (context is null)
         {
@@ -52,7 +54,7 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
         if (owner is null)
         {
             Debug.Fail("Owner should never be null.");
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         var parent = owner.Parent;
@@ -102,13 +104,13 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
                 //
                 // Will be interpreted as having an `@code` attribute name due to multi-line attributes being a thing. Ultimately this is mostly a
                 // heuristic that we have to apply in order to workaround limitations of the Razor compiler.
-                return Array.Empty<RazorCompletionItem>();
+                return ImmutableArray<RazorCompletionItem>.Empty;
             }
 
             var stringifiedAttributes = _tagHelperFactsService.StringifyAttributes(attributes);
-            var attributeCompletions = GetAttributeCompletions(parent, containingTagNameToken.Content, selectedAttributeName, stringifiedAttributes, context.TagHelperDocumentContext, context.Options);
-            return attributeCompletions;
 
+            return GetAttributeCompletions(parent, containingTagNameToken.Content, selectedAttributeName, stringifiedAttributes, context.TagHelperDocumentContext, context.Options);
+            
             static bool InOrAtEndOfAttribute(SyntaxNode attributeSyntax, int absoluteIndex)
             {
                 // When we are in the middle of writing an attribute it is treated as a minimilized one, e.g.:
@@ -123,10 +125,10 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
         }
 
         // Invalid location for TagHelper completions.
-        return Array.Empty<RazorCompletionItem>();
+        return ImmutableArray<RazorCompletionItem>.Empty;
     }
 
-    private IReadOnlyList<RazorCompletionItem> GetAttributeCompletions(
+    private ImmutableArray<RazorCompletionItem> GetAttributeCompletions(
         SyntaxNode containingAttribute,
         string containingTagName,
         string? selectedAttributeName,
@@ -148,8 +150,9 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
             ancestorIsTagHelper,
             HtmlFactsService.IsHtmlTagName);
 
-        var completionItems = new List<RazorCompletionItem>();
+        using var completionItems = new PooledArrayBuilder<RazorCompletionItem>();
         var completionResult = _tagHelperCompletionService.GetAttributeCompletions(attributeCompletionContext);
+
         foreach (var completion in completionResult.Completions)
         {
             var filterText = completion.Key;
@@ -202,13 +205,14 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
 
                 return descriptionInfo;
             });
+
             var attributeDescriptionInfo = new AggregateBoundAttributeDescription(attributeDescriptions.ToList());
             razorCompletionItem.SetAttributeCompletionDescription(attributeDescriptionInfo);
 
             completionItems.Add(razorCompletionItem);
         }
 
-        return completionItems;
+        return completionItems.DrainToImmutable();
     }
 
     private bool TryResolveInsertText(string baseInsertText, AttributeContext context, [NotNullWhen(true)] out string? snippetText)
@@ -231,7 +235,7 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
         return false;
     }
 
-    private IReadOnlyList<RazorCompletionItem> GetElementCompletions(
+    private ImmutableArray<RazorCompletionItem> GetElementCompletions(
         SyntaxNode containingElement,
         string containingTagName,
         IEnumerable<KeyValuePair<string, string>> attributes,
@@ -248,7 +252,7 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
             ancestorIsTagHelper,
             HtmlFactsService.IsHtmlTagName);
 
-        var completionItems = new List<RazorCompletionItem>();
+        using var completionItems = new PooledArrayBuilder<RazorCompletionItem>();
         var completionResult = _tagHelperCompletionService.GetElementCompletions(elementCompletionContext);
         foreach (var completion in completionResult.Completions)
         {
@@ -265,7 +269,7 @@ internal class TagHelperCompletionProvider : RazorCompletionItemProvider
             completionItems.Add(razorCompletionItem);
         }
 
-        return completionItems;
+        return completionItems.DrainToImmutable();
     }
 
     private const string BooleanTypeString = "System.Boolean";

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Extensions/IServiceCollectionExtensions.cs

@@ -93,13 +93,13 @@ internal static class IServiceCollectionExtensions
         services.AddSingleton<CompletionItemResolver, RazorCompletionItemResolver>();
         services.AddSingleton<CompletionItemResolver, DelegatedCompletionItemResolver>();
         services.AddSingleton<TagHelperCompletionService, LanguageServerTagHelperCompletionService>();
-        services.AddSingleton<RazorCompletionFactsService, DefaultRazorCompletionFactsService>();
+        services.AddSingleton<IRazorCompletionFactsService, RazorCompletionFactsService>();
-        services.AddSingleton<RazorCompletionItemProvider, DirectiveCompletionItemProvider>();
+        services.AddSingleton<IRazorCompletionItemProvider, DirectiveCompletionItemProvider>();
-        services.AddSingleton<RazorCompletionItemProvider, DirectiveAttributeCompletionItemProvider>();
+        services.AddSingleton<IRazorCompletionItemProvider, DirectiveAttributeCompletionItemProvider>();
-        services.AddSingleton<RazorCompletionItemProvider, DirectiveAttributeParameterCompletionItemProvider>();
+        services.AddSingleton<IRazorCompletionItemProvider, DirectiveAttributeParameterCompletionItemProvider>();
-        services.AddSingleton<RazorCompletionItemProvider, DirectiveAttributeTransitionCompletionItemProvider>();
+        services.AddSingleton<IRazorCompletionItemProvider, DirectiveAttributeTransitionCompletionItemProvider>();
-        services.AddSingleton<RazorCompletionItemProvider, MarkupTransitionCompletionItemProvider>();
+        services.AddSingleton<IRazorCompletionItemProvider, MarkupTransitionCompletionItemProvider>();
-        services.AddSingleton<RazorCompletionItemProvider, TagHelperCompletionProvider>();
+        services.AddSingleton<IRazorCompletionItemProvider, TagHelperCompletionProvider>();
     }
 
     public static void AddDiagnosticServices(this IServiceCollection services)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/DefaultRazorCompletionFactsService.cs

@@ -1,50 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the MIT license. See License.txt in the project root for license information.
-
-using System;
-using System.Collections.Generic;
-using System.Composition;
-using System.Linq;
-
-namespace Microsoft.CodeAnalysis.Razor.Completion;
-
-[Shared]
-[Export(typeof(RazorCompletionFactsService))]
-internal class DefaultRazorCompletionFactsService : RazorCompletionFactsService
-{
-    private readonly IReadOnlyList<RazorCompletionItemProvider> _completionItemProviders;
-
-    [ImportingConstructor]
-    public DefaultRazorCompletionFactsService([ImportMany] IEnumerable<RazorCompletionItemProvider> completionItemProviders)
-    {
-        if (completionItemProviders is null)
-        {
-            throw new ArgumentNullException(nameof(completionItemProviders));
-        }
-
-        _completionItemProviders = completionItemProviders.ToArray();
-    }
-
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
-    {
-        if (context is null)
-        {
-            throw new ArgumentNullException(nameof(context));
-        }
-
-        if (context.TagHelperDocumentContext is null)
-        {
-            throw new ArgumentNullException(nameof(context.TagHelperDocumentContext));
-        }
-
-        var completions = new List<RazorCompletionItem>();
-        for (var i = 0; i < _completionItemProviders.Count; i++)
-        {
-            var completionItemProvider = _completionItemProviders[i];
-            var items = completionItemProvider.GetCompletionItems(context);
-            completions.AddRange(items);
-        }
-
-        return completions;
-    }
-}

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/DirectiveAttributeCompletionItemProvider.cs

@@ -5,20 +5,20 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Composition;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor.Tooltip;
 using Microsoft.VisualStudio.Editor.Razor;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
 [Shared]
-[Export(typeof(RazorCompletionItemProvider))]
+[Export(typeof(IRazorCompletionItemProvider))]
 internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeCompletionItemProviderBase
 {
-    private static readonly RazorCompletionItem[] s_noDirectiveAttributeCompletionItems = Array.Empty<RazorCompletionItem>();
-
     private readonly TagHelperFactsService _tagHelperFactsService;
 
     [ImportingConstructor]
@@ -32,7 +32,7 @@ internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeComp
         _tagHelperFactsService = tagHelperFactsService;
     }
 
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    public override ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
         if (context is null)
         {
@@ -47,31 +47,31 @@ internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeComp
         if (!FileKinds.IsComponent(context.SyntaxTree.Options.FileKind))
         {
             // Directive attributes are only supported in components
-            return s_noDirectiveAttributeCompletionItems;
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         var owner = context.Owner;
         if (owner is null)
         {
-            return s_noDirectiveAttributeCompletionItems;
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!TryGetAttributeInfo(owner, out _, out var attributeName, out var attributeNameLocation, out _, out _))
         {
             // Either we're not in an attribute or the attribute is so malformed that we can't provide proper completions.
-            return s_noDirectiveAttributeCompletionItems;
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!attributeNameLocation.IntersectsWith(context.AbsoluteIndex))
         {
             // We're trying to retrieve completions on a portion of the name that is not supported (such as a parameter).
-            return s_noDirectiveAttributeCompletionItems;
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!TryGetElementInfo(owner.Parent.Parent, out var containingTagName, out var attributes))
         {
             // This should never be the case, it means that we're operating on an attribute that doesn't have a tag.
-            return s_noDirectiveAttributeCompletionItems;
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         // At this point we've determined that completions have been requested for the name portion of the selected attribute.
@@ -86,11 +86,11 @@ internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeComp
             return completionItems;
         }
 
-        return s_noDirectiveAttributeCompletionItems;
+        return ImmutableArray<RazorCompletionItem>.Empty;
     }
 
     // Internal for testing
-    internal IReadOnlyList<RazorCompletionItem> GetAttributeCompletions(
+    internal ImmutableArray<RazorCompletionItem> GetAttributeCompletions(
         string selectedAttributeName,
         string containingTagName,
         IEnumerable<string> attributes,
@@ -100,7 +100,7 @@ internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeComp
         if (descriptorsForTag.Count == 0)
         {
             // If the current tag has no possible descriptors then we can't have any directive attributes.
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         // Attributes are case sensitive when matching
@@ -141,7 +141,8 @@ internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeComp
             }
         }
 
-        var completionItems = new List<RazorCompletionItem>();
+        using var completionItems = new PooledArrayBuilder<RazorCompletionItem>();
+
         foreach (var completion in attributeCompletions)
         {
             var insertText = completion.Key;
@@ -173,7 +174,7 @@ internal class DirectiveAttributeCompletionItemProvider : DirectiveAttributeComp
             completionItems.Add(razorCompletionItem);
         }
 
-        return completionItems;
+        return completionItems.DrainToImmutable();
 
         bool TryAddCompletion(string attributeName, BoundAttributeDescriptor boundAttributeDescriptor, TagHelperDescriptor tagHelperDescriptor)
         {

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/DirectiveAttributeCompletionItemProviderBase.cs

@@ -5,14 +5,17 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
 using RazorSyntaxList = Microsoft.AspNetCore.Razor.Language.Syntax.SyntaxList<Microsoft.AspNetCore.Razor.Language.Syntax.SyntaxNode>;
 using RazorSyntaxNode = Microsoft.AspNetCore.Razor.Language.Syntax.SyntaxNode;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
-internal abstract class DirectiveAttributeCompletionItemProviderBase : RazorCompletionItemProvider
+internal abstract class DirectiveAttributeCompletionItemProviderBase : IRazorCompletionItemProvider
 {
+    public abstract ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context);
+
     // Internal for testing
     internal static bool TryGetAttributeInfo(
         RazorSyntaxNode attributeLeafOwner,

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/DirectiveAttributeParameterCompletionItemProvider.cs

@@ -5,16 +5,18 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Composition;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor.Tooltip;
 using Microsoft.VisualStudio.Editor.Razor;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
 [Shared]
-[Export(typeof(RazorCompletionItemProvider))]
+[Export(typeof(IRazorCompletionItemProvider))]
 internal class DirectiveAttributeParameterCompletionItemProvider : DirectiveAttributeCompletionItemProviderBase
 {
     private readonly TagHelperFactsService _tagHelperFactsService;
@@ -30,7 +32,7 @@ internal class DirectiveAttributeParameterCompletionItemProvider : DirectiveAttr
         _tagHelperFactsService = tagHelperFactsService;
     }
 
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    public override ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
         if (context is null)
         {
@@ -45,39 +47,38 @@ internal class DirectiveAttributeParameterCompletionItemProvider : DirectiveAttr
         if (!FileKinds.IsComponent(context.SyntaxTree.Options.FileKind))
         {
             // Directive attribute parameters are only supported in components
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         var owner = context.Owner;
         if (owner is null)
         {
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!TryGetAttributeInfo(owner, out _, out var attributeName, out _, out var parameterName, out var parameterNameLocation))
         {
             // Either we're not in an attribute or the attribute is so malformed that we can't provide proper completions.
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!parameterNameLocation.IntersectsWith(context.AbsoluteIndex))
         {
             // We're trying to retrieve completions on a portion of the name that is not supported (such as the name, i.e., |@bind|:format).
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!TryGetElementInfo(owner.Parent.Parent, out var containingTagName, out var attributes))
         {
             // This should never be the case, it means that we're operating on an attribute that doesn't have a tag.
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
-        var completions = GetAttributeParameterCompletions(attributeName, parameterName, containingTagName, attributes, context.TagHelperDocumentContext);
+        return GetAttributeParameterCompletions(attributeName, parameterName, containingTagName, attributes, context.TagHelperDocumentContext);
-        return completions;
     }
 
     // Internal for testing
-    internal IReadOnlyList<RazorCompletionItem> GetAttributeParameterCompletions(
+    internal ImmutableArray<RazorCompletionItem> GetAttributeParameterCompletions(
         string attributeName,
         string parameterName,
         string containingTagName,
@@ -88,7 +89,7 @@ internal class DirectiveAttributeParameterCompletionItemProvider : DirectiveAttr
         if (descriptorsForTag.Count == 0)
         {
             // If the current tag has no possible descriptors then we can't have any additional attributes.
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         // Attribute parameters are case sensitive when matching
@@ -130,7 +131,8 @@ internal class DirectiveAttributeParameterCompletionItemProvider : DirectiveAttr
             }
         }
 
-        var completionItems = new List<RazorCompletionItem>();
+        using var completionItems = new PooledArrayBuilder<RazorCompletionItem>();
+
         foreach (var completion in attributeCompletions)
         {
             if (string.Equals(completion.Key, parameterName, StringComparison.Ordinal))
@@ -150,6 +152,6 @@ internal class DirectiveAttributeParameterCompletionItemProvider : DirectiveAttr
             completionItems.Add(razorCompletionItem);
         }
 
-        return completionItems;
+        return completionItems.DrainToImmutable();
     }
 }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/DirectiveCompletionItemProvider.cs

@@ -5,17 +5,19 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Composition;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
 [Shared]
-[Export(typeof(RazorCompletionItemProvider))]
+[Export(typeof(IRazorCompletionItemProvider))]
-internal class DirectiveCompletionItemProvider : RazorCompletionItemProvider
+internal class DirectiveCompletionItemProvider : IRazorCompletionItemProvider
 {
     internal static readonly IReadOnlyList<RazorCommitCharacter> SingleLineDirectiveCommitCharacters = RazorCommitCharacter.FromArray(new[] { " " });
     internal static readonly IReadOnlyList<RazorCommitCharacter> BlockDirectiveCommitCharacters = RazorCommitCharacter.FromArray(new[] { " ", "{" });
@@ -46,21 +48,22 @@ internal class DirectiveCompletionItemProvider : RazorCompletionItemProvider
         ["typeparam"] = ("typeparam ${1:T}$0", "typeparam T")
     };
 
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    public ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
         if (context is null)
         {
             throw new ArgumentNullException(nameof(context));
         }
 
-        var completions = new List<RazorCompletionItem>();
+        using var completions = new PooledArrayBuilder<RazorCompletionItem>();
+
         if (ShouldProvideCompletions(context))
         {
             var directiveCompletions = GetDirectiveCompletionItems(context.SyntaxTree);
             completions.AddRange(directiveCompletions);
         }
 
-        return completions;
+        return completions.DrainToImmutable();
     }
 
     // Internal for testing
@@ -126,11 +129,13 @@ internal class DirectiveCompletionItemProvider : RazorCompletionItemProvider
     }
 
     // Internal for testing
-    internal static List<RazorCompletionItem> GetDirectiveCompletionItems(RazorSyntaxTree syntaxTree)
+    internal static ImmutableArray<RazorCompletionItem> GetDirectiveCompletionItems(RazorSyntaxTree syntaxTree)
     {
         var defaultDirectives = FileKinds.IsComponent(syntaxTree.Options.FileKind) ? Array.Empty<DirectiveDescriptor>() : s_defaultDirectives;
         var directives = syntaxTree.Options.Directives.Concat(defaultDirectives);
-        var completionItems = new List<RazorCompletionItem>();
+
+        using var completionItems = new PooledArrayBuilder<RazorCompletionItem>();
+
         foreach (var directive in directives)
         {
             var completionDisplayText = directive.DisplayName ?? directive.Directive;
@@ -164,7 +169,7 @@ internal class DirectiveCompletionItemProvider : RazorCompletionItemProvider
             }
         }
 
-        return completionItems;
+        return completionItems.DrainToImmutable();
     }
 
     private static IReadOnlyList<RazorCommitCharacter> GetDirectiveCommitCharacters(DirectiveKind directiveKind)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/IRazorCompletionFactsService.cs

@@ -1,11 +1,11 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
-using System.Collections.Generic;
+using System.Collections.Immutable;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
-internal abstract class RazorCompletionItemProvider
+internal interface IRazorCompletionFactsService
 {
-    public abstract IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context);
+    ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext razorCompletionContext);
 }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/IRazorCompletionItemProvider.cs

@@ -0,0 +1,11 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Collections.Immutable;
+
+namespace Microsoft.CodeAnalysis.Razor.Completion;
+
+internal interface IRazorCompletionItemProvider
+{
+    ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context);
+}

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/MarkupTransitionCompletionItemProvider.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Diagnostics;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
@@ -11,7 +12,7 @@ using RazorSyntaxNode = Microsoft.AspNetCore.Razor.Language.Syntax.SyntaxNode;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
-internal class MarkupTransitionCompletionItemProvider : RazorCompletionItemProvider
+internal class MarkupTransitionCompletionItemProvider : IRazorCompletionItemProvider
 {
     private static readonly IReadOnlyList<RazorCommitCharacter> s_elementCommitCharacters = RazorCommitCharacter.FromArray(new[] { ">" });
 
@@ -40,15 +41,10 @@ internal class MarkupTransitionCompletionItemProvider : RazorCompletionItemProvi
 
     public MarkupTransitionCompletionItemProvider(HtmlFactsService htmlFactsService)
     {
-        if (htmlFactsService is null)
+        _htmlFactsService = htmlFactsService ?? throw new ArgumentNullException(nameof(htmlFactsService));
-        {
-            throw new ArgumentNullException(nameof(htmlFactsService));
-        }
-
-        _htmlFactsService = htmlFactsService;
     }
 
-    public override IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    public ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
     {
         if (context is null)
         {
@@ -59,12 +55,12 @@ internal class MarkupTransitionCompletionItemProvider : RazorCompletionItemProvi
         if (owner is null)
         {
             Debug.Fail("Owner should never be null.");
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         if (!AtMarkupTransitionCompletionPoint(owner))
         {
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
         var parent = owner.Parent;
@@ -74,11 +70,10 @@ internal class MarkupTransitionCompletionItemProvider : RazorCompletionItemProvi
         if (!_htmlFactsService.TryGetElementInfo(parent, out var containingTagNameToken, out _) ||
             !containingTagNameToken.Span.IntersectsWith(context.AbsoluteIndex))
         {
-            return Array.Empty<RazorCompletionItem>();
+            return ImmutableArray<RazorCompletionItem>.Empty;
         }
 
-        var completions = new List<RazorCompletionItem>() { MarkupTransitionCompletionItem };
+        return ImmutableArray.Create(MarkupTransitionCompletionItem);
-        return completions;
     }
 
     private static bool AtMarkupTransitionCompletionPoint(RazorSyntaxNode owner)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/RazorCompletionFactsService.cs

@@ -1,11 +1,51 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Composition;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
-internal abstract class RazorCompletionFactsService
+[Shared]
+[Export(typeof(IRazorCompletionFactsService))]
+internal class RazorCompletionFactsService : IRazorCompletionFactsService
 {
-    public abstract IReadOnlyList<RazorCompletionItem> GetCompletionItems(RazorCompletionContext razorCompletionContext);
+    private readonly ImmutableArray<IRazorCompletionItemProvider> _providers;
+
+    [ImportingConstructor]
+    public RazorCompletionFactsService([ImportMany] IEnumerable<IRazorCompletionItemProvider> providers)
+    {
+        if (providers is null)
+        {
+            throw new ArgumentNullException(nameof(providers));
+        }
+
+        _providers = providers.ToImmutableArray();
+    }
+
+    public ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionContext context)
+    {
+        if (context is null)
+        {
+            throw new ArgumentNullException(nameof(context));
+        }
+
+        if (context.TagHelperDocumentContext is null)
+        {
+            throw new ArgumentNullException(nameof(context.TagHelperDocumentContext));
+        }
+
+        using var completions = new PooledArrayBuilder<RazorCompletionItem>();
+
+        foreach (var provider in _providers)
+        {
+            var items = provider.GetCompletionItems(context);
+            completions.AddRange(items);
+        }
+
+        return completions.DrainToImmutable();
+    }
 }

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/CompletionItemDisplayTextComparer.cs

@@ -0,0 +1,42 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using Microsoft.VisualStudio.Language.Intellisense.AsyncCompletion.Data;
+
+namespace Microsoft.VisualStudio.Editor.Razor.Completion;
+
+/// <summary>
+///  Compares <see cref="CompletionItem"/>s by display text using the current culture.
+/// </summary>
+internal sealed class CompletionItemDisplayTextComparer : IComparer<CompletionItem>
+{
+    public static readonly CompletionItemDisplayTextComparer Instance = new();
+
+    private CompletionItemDisplayTextComparer()
+    {
+    }
+
+    public int Compare(CompletionItem x, CompletionItem y)
+    {
+        var displayText1 = x?.DisplayText;
+        var displayText2 = y?.DisplayText;
+
+        if (displayText1 is null)
+        {
+            if (displayText2 is not null)
+            {
+                return -1;
+            }
+
+            return 0;
+        }
+        else if (displayText2 is null)
+        {
+            return 1;
+        }
+
+        return StringComparer.CurrentCulture.Compare(displayText1, displayText2);
+    }
+}

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/DefaultVisualStudioDescriptionFactory.cs

@@ -1,115 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the MIT license. See License.txt in the project root for license information.
-
-using System;
-using System.Collections.Generic;
-using System.Composition;
-using Microsoft.CodeAnalysis.Razor.Tooltip;
-using Microsoft.VisualStudio.Core.Imaging;
-using Microsoft.VisualStudio.Text.Adornments;
-
-namespace Microsoft.VisualStudio.Editor.Razor.Completion;
-
-[Shared]
-[Export(typeof(VisualStudioDescriptionFactory))]
-internal class DefaultVisualStudioDescriptionFactory : VisualStudioDescriptionFactory
-{
-    // Internal for testing
-    internal static readonly ContainerElement SeparatorElement = new(
-        ContainerElementStyle.Wrapped,
-        new ClassifiedTextElement(
-            new ClassifiedTextRun(PredefinedClassificationNames.Comment, "------------")));
-
-    // Hardcoding the Guid here to avoid a reference to Microsoft.VisualStudio.ImageCatalog.dll
-    // that is not present in Visual Studio for Mac
-    private static readonly Guid s_imageCatalogGuid = new("{ae27a6b0-e345-4288-96df-5eaf394ee369}");
-    private static readonly ImageElement s_propertyGlyph = new(
-        new ImageId(s_imageCatalogGuid, 2429), // KnownImageIds.Type = 2429
-        "Razor Attribute Glyph");
-    private static readonly ClassifiedTextRun s_spaceLiteral = new(PredefinedClassificationNames.Literal, " ");
-    private static readonly ClassifiedTextRun s_dotLiteral = new(PredefinedClassificationNames.Literal, ".");
-
-    public override ContainerElement CreateClassifiedDescription(AggregateBoundAttributeDescription completionDescription)
-    {
-        if (completionDescription is null)
-        {
-            throw new ArgumentNullException(nameof(completionDescription));
-        }
-
-        var descriptionElements = new List<object>();
-        foreach (var descriptionInfo in completionDescription.DescriptionInfos)
-        {
-            if (descriptionElements.Count > 0)
-            {
-                descriptionElements.Add(SeparatorElement);
-            }
-
-            var returnTypeClassification = PredefinedClassificationNames.Type;
-            if (TypeNameStringResolver.TryGetSimpleName(descriptionInfo.ReturnTypeName, out var returnTypeName))
-            {
-                returnTypeClassification = PredefinedClassificationNames.Keyword;
-            }
-            else
-            {
-                returnTypeName = descriptionInfo.ReturnTypeName;
-            }
-
-            var tagHelperTypeName = descriptionInfo.TypeName;
-            var tagHelperTypeNamePrefix = string.Empty;
-            var tagHelperTypeNameProper = tagHelperTypeName;
-
-            var lastDot = tagHelperTypeName.LastIndexOf('.');
-            if (lastDot > 0)
-            {
-                var afterLastDot = lastDot + 1;
-
-                // We're pulling apart the type name so the prefix looks like:
-                //
-                // Microsoft.AspnetCore.Components.
-                tagHelperTypeNamePrefix = tagHelperTypeName[..afterLastDot];
-
-                // And the type name looks like BindBinds
-                tagHelperTypeNameProper = tagHelperTypeName[afterLastDot..];
-            }
-
-            descriptionElements.Add(
-                new ContainerElement(
-                    ContainerElementStyle.Wrapped,
-                    s_propertyGlyph,
-                    new ClassifiedTextElement(
-                        new ClassifiedTextRun(returnTypeClassification, returnTypeName),
-                        s_spaceLiteral,
-                        new ClassifiedTextRun(PredefinedClassificationNames.Literal, tagHelperTypeNamePrefix),
-                        new ClassifiedTextRun(PredefinedClassificationNames.Type, tagHelperTypeNameProper),
-                        s_dotLiteral,
-                        new ClassifiedTextRun(PredefinedClassificationNames.Identifier, descriptionInfo.PropertyName))));
-
-            if (descriptionInfo.Documentation != null)
-            {
-                descriptionElements.Add(
-                    new ContainerElement(
-                        ContainerElementStyle.Wrapped,
-                        new ClassifiedTextElement(
-                            new ClassifiedTextRun(PredefinedClassificationNames.NaturalLanguage, descriptionInfo.Documentation))));
-            }
-        }
-
-        var descriptionContainer = new ContainerElement(ContainerElementStyle.Stacked, descriptionElements);
-        return descriptionContainer;
-    }
-
-    private static class PredefinedClassificationNames
-    {
-        public const string Keyword = "keyword";
-
-        public const string Literal = "literal";
-
-        public const string Type = "Type";
-
-        public const string Identifier = "identifier";
-
-        public const string Comment = "comment";
-
-        public const string NaturalLanguage = "natural language";
-    }
-}

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/IVisualStudioDescriptionFactory.cs

@@ -0,0 +1,12 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using Microsoft.CodeAnalysis.Razor.Tooltip;
+using Microsoft.VisualStudio.Text.Adornments;
+
+namespace Microsoft.VisualStudio.Editor.Razor.Completion;
+
+internal interface IVisualStudioDescriptionFactory
+{
+    ContainerElement CreateClassifiedDescription(AggregateBoundAttributeDescription description);
+}

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/RazorDirectiveAttributeCompletionSource.cs

@@ -4,11 +4,11 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
-using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor;
 using Microsoft.CodeAnalysis.Razor.Completion;
 using Microsoft.CodeAnalysis.Razor.Tooltip;
@@ -38,45 +38,25 @@ internal class RazorDirectiveAttributeCompletionSource : IAsyncCompletionSource
     }.ToImmutableArray();
 
     private readonly VisualStudioRazorParser _parser;
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
     private readonly ICompletionBroker _completionBroker;
-    private readonly VisualStudioDescriptionFactory _descriptionFactory;
+    private readonly IVisualStudioDescriptionFactory _descriptionFactory;
     private readonly JoinableTaskFactory _joinableTaskFactory;
     private readonly ProjectSnapshotManagerDispatcher _projectSnapshotManagerDispatcher;
 
     public RazorDirectiveAttributeCompletionSource(
         ProjectSnapshotManagerDispatcher projectSnapshotManagerDispatcher,
         VisualStudioRazorParser parser,
-        RazorCompletionFactsService completionFactsService,
+        IRazorCompletionFactsService completionFactsService,
         ICompletionBroker completionBroker,
-        VisualStudioDescriptionFactory descriptionFactory,
+        IVisualStudioDescriptionFactory descriptionFactory,
         JoinableTaskFactory joinableTaskFactory)
     {
-        if (projectSnapshotManagerDispatcher is null)
+        _projectSnapshotManagerDispatcher = projectSnapshotManagerDispatcher ?? throw new ArgumentNullException(nameof(projectSnapshotManagerDispatcher));
-        {
+        _parser = parser ?? throw new ArgumentNullException(nameof(parser));
-            throw new ArgumentNullException(nameof(projectSnapshotManagerDispatcher));
+        _completionFactsService = completionFactsService ?? throw new ArgumentNullException(nameof(completionFactsService));
-        }
-
-        if (parser is null)
-        {
-            throw new ArgumentNullException(nameof(parser));
-        }
-
-        if (completionFactsService is null)
-        {
-            throw new ArgumentNullException(nameof(completionFactsService));
-        }
-
-        if (descriptionFactory is null)
-        {
-            throw new ArgumentNullException(nameof(descriptionFactory));
-        }
-
-        _projectSnapshotManagerDispatcher = projectSnapshotManagerDispatcher;
-        _parser = parser;
-        _completionFactsService = completionFactsService;
         _completionBroker = completionBroker;
-        _descriptionFactory = descriptionFactory;
+        _descriptionFactory = descriptionFactory ?? throw new ArgumentNullException(nameof(descriptionFactory));
         _joinableTaskFactory = joinableTaskFactory;
     }
 
@@ -99,7 +79,7 @@ internal class RazorDirectiveAttributeCompletionSource : IAsyncCompletionSource
             var razorCompletionContext = new RazorCompletionContext(absoluteIndex, owner, syntaxTree, tagHelperDocumentContext);
             var razorCompletionItems = _completionFactsService.GetCompletionItems(razorCompletionContext);
 
-            if (razorCompletionItems.Count == 0)
+            if (razorCompletionItems.Length == 0)
             {
                 return CompletionContext.Empty;
             }
@@ -121,8 +101,9 @@ internal class RazorDirectiveAttributeCompletionSource : IAsyncCompletionSource
                 activeSession.Dismiss();
             }
 
-            var completionItems = new List<CompletionItem>();
+            using var _ = ArrayBuilderPool<CompletionItem>.GetPooledObject(out var completionItems);
             var completionItemKinds = new HashSet<RazorCompletionItemKind>();
+
             foreach (var razorCompletionItem in razorCompletionItems)
             {
                 if (razorCompletionItem.Kind != RazorCompletionItemKind.DirectiveAttribute &&
@@ -150,9 +131,10 @@ internal class RazorDirectiveAttributeCompletionSource : IAsyncCompletionSource
             }
 
             session.Properties.SetCompletionItemKinds(completionItemKinds);
-            var orderedCompletionItems = completionItems.OrderBy(item => item.DisplayText);
+
-            var context = new CompletionContext(orderedCompletionItems.ToImmutableArray());
+            completionItems.Sort(CompletionItemDisplayTextComparer.Instance);
-            return context;
+
+            return new CompletionContext(completionItems.ToImmutable());
         }
         catch (OperationCanceledException)
         {

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/RazorDirectiveAttributeCompletionSourceProvider.cs

@@ -23,50 +23,24 @@ namespace Microsoft.VisualStudio.Editor.Razor.Completion;
 internal class RazorDirectiveAttributeCompletionSourceProvider : IAsyncCompletionSourceProvider
 {
     private readonly ProjectSnapshotManagerDispatcher _projectSnapshotManagerDispatcher;
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
     private readonly ICompletionBroker _completionBroker;
-    private readonly VisualStudioDescriptionFactory _descriptionFactory;
+    private readonly IVisualStudioDescriptionFactory _descriptionFactory;
     private readonly JoinableTaskContext _joinableTaskContext;
 
     [ImportingConstructor]
     public RazorDirectiveAttributeCompletionSourceProvider(
         ProjectSnapshotManagerDispatcher projectSnapshotManagerDispatcher,
-        RazorCompletionFactsService completionFactsService,
+        IRazorCompletionFactsService completionFactsService,
-        IAsyncCompletionBroker asyncCoompletionBroker,
         ICompletionBroker completionBroker,
-        VisualStudioDescriptionFactory descriptionFactory,
+        IVisualStudioDescriptionFactory descriptionFactory,
         JoinableTaskContext joinableTaskContext)
     {
-        if (projectSnapshotManagerDispatcher is null)
+        _projectSnapshotManagerDispatcher = projectSnapshotManagerDispatcher ?? throw new ArgumentNullException(nameof(projectSnapshotManagerDispatcher));
-        {
+        _completionFactsService = completionFactsService ?? throw new ArgumentNullException(nameof(completionFactsService));
-            throw new ArgumentNullException(nameof(projectSnapshotManagerDispatcher));
+        _completionBroker = completionBroker ?? throw new ArgumentNullException(nameof(completionBroker));
-        }
+        _descriptionFactory = descriptionFactory ?? throw new ArgumentNullException(nameof(descriptionFactory));
-
+        _joinableTaskContext = joinableTaskContext ?? throw new ArgumentNullException(nameof(joinableTaskContext));
-        if (completionFactsService is null)
-        {
-            throw new ArgumentNullException(nameof(completionFactsService));
-        }
-
-        if (asyncCoompletionBroker is null)
-        {
-            throw new ArgumentNullException(nameof(asyncCoompletionBroker));
-        }
-
-        if (descriptionFactory is null)
-        {
-            throw new ArgumentNullException(nameof(descriptionFactory));
-        }
-
-        if (joinableTaskContext is null)
-        {
-            throw new ArgumentNullException(nameof(joinableTaskContext));
-        }
-
-        _projectSnapshotManagerDispatcher = projectSnapshotManagerDispatcher;
-        _completionFactsService = completionFactsService;
-        _completionBroker = completionBroker;
-        _descriptionFactory = descriptionFactory;
-        _joinableTaskContext = joinableTaskContext;
     }
 
     public IAsyncCompletionSource? GetOrCreate(ITextView textView)
@@ -96,13 +70,12 @@ internal class RazorDirectiveAttributeCompletionSourceProvider : IAsyncCompletio
             return null;
         }
 
-        var completionSource = new RazorDirectiveAttributeCompletionSource(
+        return new RazorDirectiveAttributeCompletionSource(
             _projectSnapshotManagerDispatcher,
             parser,
             _completionFactsService,
             _completionBroker,
             _descriptionFactory,
             _joinableTaskContext.Factory);
-        return completionSource;
     }
 }

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/RazorDirectiveCompletionSource.cs

@@ -2,12 +2,12 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.Razor.Completion;
 using Microsoft.VisualStudio.Core.Imaging;
 using Microsoft.VisualStudio.Language.Intellisense.AsyncCompletion;
@@ -33,11 +33,11 @@ internal class RazorDirectiveCompletionSource : IAsyncCompletionSource
 
     // Internal for testing
     internal readonly VisualStudioRazorParser Parser;
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
 
     public RazorDirectiveCompletionSource(
         VisualStudioRazorParser parser,
-        RazorCompletionFactsService completionFactsService)
+        IRazorCompletionFactsService completionFactsService)
     {
         if (parser is null)
         {
@@ -77,7 +77,8 @@ internal class RazorDirectiveCompletionSource : IAsyncCompletionSource
             var razorCompletionContext = new RazorCompletionContext(absoluteIndex, owner, syntaxTree, tagHelperDocumentContext);
             var razorCompletionItems = _completionFactsService.GetCompletionItems(razorCompletionContext);
 
-            var completionItems = new List<CompletionItem>();
+            using var _ = ArrayBuilderPool<CompletionItem>.GetPooledObject(out var completionItems);
+
             foreach (var razorCompletionItem in razorCompletionItems)
             {
                 if (razorCompletionItem.Kind != RazorCompletionItemKind.Directive)
@@ -96,13 +97,13 @@ internal class RazorDirectiveCompletionSource : IAsyncCompletionSource
                     suffix: string.Empty,
                     sortText: razorCompletionItem.DisplayText,
                     attributeIcons: ImmutableArray<ImageElement>.Empty);
+
                 var completionDescription = razorCompletionItem.GetDirectiveCompletionDescription();
                 completionItem.Properties.AddProperty(DescriptionKey, completionDescription);
                 completionItems.Add(completionItem);
             }
 
-            var context = new CompletionContext(completionItems.ToImmutableArray());
+            return new CompletionContext(completionItems.ToImmutable());
-            return context;
         }
         catch (OperationCanceledException)
         {

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/RazorDirectiveCompletionSourceProvider.cs

@@ -20,10 +20,10 @@ namespace Microsoft.VisualStudio.Editor.Razor.Completion;
 [ContentType(RazorConstants.LegacyCoreContentType)]
 internal class RazorDirectiveCompletionSourceProvider : IAsyncCompletionSourceProvider
 {
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
 
     [ImportingConstructor]
-    public RazorDirectiveCompletionSourceProvider(RazorCompletionFactsService completionFactsService)
+    public RazorDirectiveCompletionSourceProvider(IRazorCompletionFactsService completionFactsService)
     {
         if (completionFactsService is null)
         {

src/Razor/src/Microsoft.VisualStudio.Editor.Razor/Completion/VisualStudioDescriptionFactory.cs

@@ -1,12 +1,114 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
+using System;
+using System.Collections.Generic;
+using System.Composition;
 using Microsoft.CodeAnalysis.Razor.Tooltip;
+using Microsoft.VisualStudio.Core.Imaging;
 using Microsoft.VisualStudio.Text.Adornments;
 
 namespace Microsoft.VisualStudio.Editor.Razor.Completion;
 
-internal abstract class VisualStudioDescriptionFactory
+[Shared]
+[Export(typeof(IVisualStudioDescriptionFactory))]
+internal class VisualStudioDescriptionFactory : IVisualStudioDescriptionFactory
 {
-    public abstract ContainerElement CreateClassifiedDescription(AggregateBoundAttributeDescription completionDescription);
+    // Internal for testing
+    internal static readonly ContainerElement SeparatorElement = new(
+        ContainerElementStyle.Wrapped,
+        new ClassifiedTextElement(
+            new ClassifiedTextRun(PredefinedClassificationNames.Comment, "------------")));
+
+    // Hardcoding the Guid here to avoid a reference to Microsoft.VisualStudio.ImageCatalog.dll
+    // that is not present in Visual Studio for Mac
+    private static readonly Guid s_imageCatalogGuid = new("{ae27a6b0-e345-4288-96df-5eaf394ee369}");
+    private static readonly ImageElement s_propertyGlyph = new(
+        new ImageId(s_imageCatalogGuid, 2429), // KnownImageIds.Type = 2429
+        "Razor Attribute Glyph");
+    private static readonly ClassifiedTextRun s_spaceLiteral = new(PredefinedClassificationNames.Literal, " ");
+    private static readonly ClassifiedTextRun s_dotLiteral = new(PredefinedClassificationNames.Literal, ".");
+
+    public ContainerElement CreateClassifiedDescription(AggregateBoundAttributeDescription description)
+    {
+        if (description is null)
+        {
+            throw new ArgumentNullException(nameof(description));
+        }
+
+        var descriptionElements = new List<object>();
+        foreach (var descriptionInfo in description.DescriptionInfos)
+        {
+            if (descriptionElements.Count > 0)
+            {
+                descriptionElements.Add(SeparatorElement);
+            }
+
+            var returnTypeClassification = PredefinedClassificationNames.Type;
+            if (TypeNameStringResolver.TryGetSimpleName(descriptionInfo.ReturnTypeName, out var returnTypeName))
+            {
+                returnTypeClassification = PredefinedClassificationNames.Keyword;
+            }
+            else
+            {
+                returnTypeName = descriptionInfo.ReturnTypeName;
+            }
+
+            var tagHelperTypeName = descriptionInfo.TypeName;
+            var tagHelperTypeNamePrefix = string.Empty;
+            var tagHelperTypeNameProper = tagHelperTypeName;
+
+            var lastDot = tagHelperTypeName.LastIndexOf('.');
+            if (lastDot > 0)
+            {
+                var afterLastDot = lastDot + 1;
+
+                // We're pulling apart the type name so the prefix looks like:
+                //
+                // Microsoft.AspnetCore.Components.
+                tagHelperTypeNamePrefix = tagHelperTypeName[..afterLastDot];
+
+                // And the type name looks like BindBinds
+                tagHelperTypeNameProper = tagHelperTypeName[afterLastDot..];
+            }
+
+            descriptionElements.Add(
+                new ContainerElement(
+                    ContainerElementStyle.Wrapped,
+                    s_propertyGlyph,
+                    new ClassifiedTextElement(
+                        new ClassifiedTextRun(returnTypeClassification, returnTypeName),
+                        s_spaceLiteral,
+                        new ClassifiedTextRun(PredefinedClassificationNames.Literal, tagHelperTypeNamePrefix),
+                        new ClassifiedTextRun(PredefinedClassificationNames.Type, tagHelperTypeNameProper),
+                        s_dotLiteral,
+                        new ClassifiedTextRun(PredefinedClassificationNames.Identifier, descriptionInfo.PropertyName))));
+
+            if (descriptionInfo.Documentation is { } documentation)
+            {
+                descriptionElements.Add(
+                    new ContainerElement(
+                        ContainerElementStyle.Wrapped,
+                        new ClassifiedTextElement(
+                            new ClassifiedTextRun(PredefinedClassificationNames.NaturalLanguage, documentation))));
+            }
+        }
+
+        return new ContainerElement(ContainerElementStyle.Stacked, descriptionElements);
+    }
+
+    private static class PredefinedClassificationNames
+    {
+        public const string Keyword = "keyword";
+
+        public const string Literal = "literal";
+
+        public const string Type = "Type";
+
+        public const string Identifier = "identifier";
+
+        public const string Comment = "comment";
+
+        public const string NaturalLanguage = "natural language";
+    }
 }

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/LegacyRazorCompletionEndpointTest.cs

@@ -25,7 +25,7 @@ namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion;
 
 public class LegacyRazorCompletionEndpointTest : LanguageServerTestBase
 {
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
     private readonly CompletionListCache _completionListCache;
     private readonly VSInternalClientCapabilities _clientCapabilities;
 
@@ -36,7 +36,7 @@ public class LegacyRazorCompletionEndpointTest : LanguageServerTestBase
         var tagHelperFactsService = new DefaultTagHelperFactsService();
         var tagHelperCompletionService = new LanguageServerTagHelperCompletionService(tagHelperFactsService);
 
-        var completionProviders = new RazorCompletionItemProvider[]
+        var completionProviders = new IRazorCompletionItemProvider[]
         {
             new DirectiveCompletionItemProvider(),
             new DirectiveAttributeCompletionItemProvider(tagHelperFactsService),
@@ -44,7 +44,7 @@ public class LegacyRazorCompletionEndpointTest : LanguageServerTestBase
             new TagHelperCompletionProvider(tagHelperCompletionService, new DefaultHtmlFactsService(), tagHelperFactsService, TestRazorLSPOptionsMonitor.Create())
         };
 
-        _completionFactsService = new DefaultRazorCompletionFactsService(completionProviders);
+        _completionFactsService = new RazorCompletionFactsService(completionProviders);
         _completionListCache = new CompletionListCache();
         _clientCapabilities = new VSInternalClientCapabilities()
         {

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/LegacyRazorCompletionResolveEndpointTest.cs

@@ -4,7 +4,7 @@
 #nullable disable
 
 using System;
-using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
@@ -27,7 +27,6 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
     private readonly CompletionListCache _completionListCache;
     private readonly VSInternalCompletionSetting _completionCapability;
     private readonly VSInternalClientCapabilities _defaultClientCapability;
-    private readonly VSInternalClientCapabilities _vsClientCapability;
 
     public LegacyRazorCompletionResolveEndpointTest(ITestOutputHelper testOutput)
         : base(testOutput)
@@ -50,15 +49,6 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
                 Completion = _completionCapability,
             },
         };
-
-        _vsClientCapability = new VSInternalClientCapabilities()
-        {
-            TextDocument = new TextDocumentClientCapabilities()
-            {
-                Completion = _completionCapability,
-            },
-            SupportsVisualStudioExtensions = true,
-        };
     }
 
     [Fact]
@@ -69,7 +59,7 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         endpoint.ApplyCapabilities(new(), _defaultClientCapability);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.Directive);
         razorCompletionItem.SetDirectiveCompletionDescription(new DirectiveCompletionDescription("Test directive"));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single();
         var parameters = ConvertToBridgedItem(completionItem);
         var requestContext = CreateRazorRequestContext(documentContext: null);
@@ -89,7 +79,7 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         endpoint.ApplyCapabilities(new(), _defaultClientCapability);
         var razorCompletionItem = new RazorCompletionItem("@...", "@", RazorCompletionItemKind.MarkupTransition);
         razorCompletionItem.SetMarkupTransitionCompletionDescription(new MarkupTransitionCompletionDescription("Test description"));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single();
         var parameters = ConvertToBridgedItem(completionItem);
         var requestContext = CreateRazorRequestContext(documentContext: null);
@@ -117,7 +107,7 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         endpoint.ApplyCapabilities(new(), _defaultClientCapability);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.DirectiveAttribute);
         razorCompletionItem.SetAttributeCompletionDescription(new AggregateBoundAttributeDescription(Array.Empty<BoundAttributeDescriptionInfo>()));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single();
         var parameters = ConvertToBridgedItem(completionItem);
         var requestContext = CreateRazorRequestContext(documentContext: null);
@@ -145,7 +135,7 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         endpoint.ApplyCapabilities(new(), _defaultClientCapability);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.DirectiveAttributeParameter);
         razorCompletionItem.SetAttributeCompletionDescription(new AggregateBoundAttributeDescription(Array.Empty<BoundAttributeDescriptionInfo>()));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single();
         var parameters = ConvertToBridgedItem(completionItem);
         var requestContext = CreateRazorRequestContext(documentContext: null);
@@ -173,7 +163,7 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         endpoint.ApplyCapabilities(new(), _defaultClientCapability);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.TagHelperElement);
         razorCompletionItem.SetTagHelperElementDescriptionInfo(new AggregateBoundElementDescription(Array.Empty<BoundElementDescriptionInfo>()));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single();
         var parameters = ConvertToBridgedItem(completionItem);
         var requestContext = CreateRazorRequestContext(documentContext: null);
@@ -201,7 +191,7 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         endpoint.ApplyCapabilities(new(), _defaultClientCapability);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.TagHelperAttribute);
         razorCompletionItem.SetAttributeCompletionDescription(new AggregateBoundAttributeDescription(Array.Empty<BoundAttributeDescriptionInfo>()));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single();
         var parameters = ConvertToBridgedItem(completionItem);
         var requestContext = CreateRazorRequestContext(documentContext: null);
@@ -238,9 +228,9 @@ public class LegacyRazorCompletionResolveEndpointTest : LanguageServerTestBase
         Assert.Null(newCompletionItem.Documentation);
     }
 
-    private VSInternalCompletionList CreateLSPCompletionList(IReadOnlyList<RazorCompletionItem> razorCompletionItems)
+    private VSInternalCompletionList CreateLSPCompletionList(params RazorCompletionItem[] razorCompletionItems)
     {
-        var completionList = LegacyRazorCompletionEndpoint.CreateLSPCompletionList(razorCompletionItems, _defaultClientCapability);
+        var completionList = LegacyRazorCompletionEndpoint.CreateLSPCompletionList(razorCompletionItems.ToImmutableArray(), _defaultClientCapability);
         var resultId = _completionListCache.Add(completionList, razorCompletionItems);
         completionList.SetResultId(resultId, completionSetting: null);
         return completionList;

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/RazorCompletionItemResolverTest.cs

@@ -4,7 +4,7 @@
 #nullable disable
 
 using System;
-using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.LanguageServer.Tooltip;
@@ -70,7 +70,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.Directive);
         razorCompletionItem.SetDirectiveCompletionDescription(new DirectiveCompletionDescription("Test directive"));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -88,7 +88,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("@...", "@", RazorCompletionItemKind.MarkupTransition);
         razorCompletionItem.SetMarkupTransitionCompletionDescription(new MarkupTransitionCompletionDescription("Test description"));
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -106,7 +106,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.DirectiveAttribute);
         razorCompletionItem.SetAttributeCompletionDescription(_attributeDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -124,7 +124,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.DirectiveAttributeParameter);
         razorCompletionItem.SetAttributeCompletionDescription(_attributeDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -142,7 +142,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.TagHelperElement);
         razorCompletionItem.SetTagHelperElementDescriptionInfo(_elementDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -160,7 +160,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.TagHelperAttribute);
         razorCompletionItem.SetAttributeCompletionDescription(_attributeDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -178,7 +178,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.DirectiveAttribute);
         razorCompletionItem.SetAttributeCompletionDescription(_attributeDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -196,7 +196,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.DirectiveAttributeParameter);
         razorCompletionItem.SetAttributeCompletionDescription(_attributeDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -214,7 +214,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.TagHelperElement);
         razorCompletionItem.SetTagHelperElementDescriptionInfo(_elementDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -232,7 +232,7 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         var resolver = new RazorCompletionItemResolver(_lspTagHelperTooltipFactory, _vsLspTagHelperTooltipFactory);
         var razorCompletionItem = new RazorCompletionItem("TestItem", "TestItem", RazorCompletionItemKind.TagHelperAttribute);
         razorCompletionItem.SetAttributeCompletionDescription(_attributeDescription);
-        var completionList = CreateLSPCompletionList(new[] { razorCompletionItem });
+        var completionList = CreateLSPCompletionList(razorCompletionItem);
         var completionItem = completionList.Items.Single() as VSInternalCompletionItem;
 
         // Act
@@ -259,9 +259,6 @@ public class RazorCompletionItemResolverTest : LanguageServerTestBase
         Assert.Null(resolvedCompletionItem);
     }
 
-    private VSInternalCompletionList CreateLSPCompletionList(IReadOnlyList<RazorCompletionItem> razorCompletionItems)
+    private VSInternalCompletionList CreateLSPCompletionList(params RazorCompletionItem[] razorCompletionItems)
-    {
+        => RazorCompletionListProvider.CreateLSPCompletionList(razorCompletionItems.ToImmutableArray(), _defaultClientCapability);
-        var completionList = RazorCompletionListProvider.CreateLSPCompletionList(razorCompletionItems, _defaultClientCapability);
-        return completionList;
-    }
 }

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Completion/RazorCompletionListProvierTest.cs

@@ -27,7 +27,7 @@ namespace Microsoft.AspNetCore.Razor.LanguageServer.Completion;
 
 public class RazorCompletionListProvierTest : LanguageServerTestBase
 {
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
     private readonly CompletionListCache _completionListCache;
     private readonly VSInternalClientCapabilities _clientCapabilities;
     private readonly VSInternalCompletionContext _defaultCompletionContext;
@@ -35,7 +35,7 @@ public class RazorCompletionListProvierTest : LanguageServerTestBase
     public RazorCompletionListProvierTest(ITestOutputHelper testOutput)
         : base(testOutput)
     {     
-        _completionFactsService = new DefaultRazorCompletionFactsService(GetCompletionProviders());
+        _completionFactsService = new RazorCompletionFactsService(GetCompletionProviders());
         _completionListCache = new CompletionListCache();
         _clientCapabilities = new VSInternalClientCapabilities()
         {
@@ -59,7 +59,7 @@ public class RazorCompletionListProvierTest : LanguageServerTestBase
         _defaultCompletionContext = new VSInternalCompletionContext();
     }
 
-    private static IEnumerable<RazorCompletionItemProvider> GetCompletionProviders(IOptionsMonitor<RazorLSPOptions> optionsMonitor = null)
+    private static IEnumerable<IRazorCompletionItemProvider> GetCompletionProviders(IOptionsMonitor<RazorLSPOptions> optionsMonitor = null)
     {
         // Working around strong naming restriction.
         var tagHelperFactsService = new DefaultTagHelperFactsService();
@@ -67,7 +67,7 @@ public class RazorCompletionListProvierTest : LanguageServerTestBase
 
         optionsMonitor ??= TestRazorLSPOptionsMonitor.Create();
 
-        var completionProviders = new RazorCompletionItemProvider[]
+        var completionProviders = new IRazorCompletionItemProvider[]
         {
             new DirectiveCompletionItemProvider(),
             new DirectiveAttributeCompletionItemProvider(tagHelperFactsService),
@@ -582,7 +582,7 @@ public class RazorCompletionListProvierTest : LanguageServerTestBase
         var optionsMonitor = TestRazorLSPOptionsMonitor.Create();
         await optionsMonitor.UpdateAsync(optionsMonitor.CurrentValue with { AutoInsertAttributeQuotes = false }, DisposalToken);
 
-        var completionFactsService = new DefaultRazorCompletionFactsService(GetCompletionProviders(optionsMonitor));
+        var completionFactsService = new RazorCompletionFactsService(GetCompletionProviders(optionsMonitor));
         var provider = new RazorCompletionListProvider(completionFactsService, _completionListCache, LoggerFactory);
 
         // Act

src/Razor/test/Microsoft.CodeAnalysis.Razor.Workspaces.Test/Completion/DefaultRazorCompletionFactsServiceTest.cs

@@ -3,6 +3,7 @@
 
 #nullable disable
 
+using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Test.Common;
@@ -12,13 +13,8 @@ using Xunit.Abstractions;
 
 namespace Microsoft.CodeAnalysis.Razor.Completion;
 
-public class DefaultRazorCompletionFactsServiceTest : TestBase
+public class DefaultRazorCompletionFactsServiceTest(ITestOutputHelper testOutput) : TestBase(testOutput)
 {
-    public DefaultRazorCompletionFactsServiceTest(ITestOutputHelper testOutput)
-        : base(testOutput)
-    {
-    }
-
     [Fact]
     public void GetDirectiveCompletionItems_AllProvidersCompletionItems()
     {
@@ -27,10 +23,10 @@ public class DefaultRazorCompletionFactsServiceTest : TestBase
         var tagHelperDocumentContext = TagHelperDocumentContext.Create(prefix: null, Enumerable.Empty<TagHelperDescriptor>());
         var completionItem1 = new RazorCompletionItem("displayText1", "insertText1", RazorCompletionItemKind.Directive);
         var context = new RazorCompletionContext(0, null, syntaxTree, tagHelperDocumentContext);
-        var provider1 = Mock.Of<RazorCompletionItemProvider>(p => p.GetCompletionItems(context) == new[] { completionItem1 }, MockBehavior.Strict);
+        var provider1 = Mock.Of<IRazorCompletionItemProvider>(p => p.GetCompletionItems(context) == ImmutableArray.Create(completionItem1), MockBehavior.Strict);
         var completionItem2 = new RazorCompletionItem("displayText2", "insertText2", RazorCompletionItemKind.Directive);
-        var provider2 = Mock.Of<RazorCompletionItemProvider>(p => p.GetCompletionItems(context) == new[] { completionItem2 }, MockBehavior.Strict);
+        var provider2 = Mock.Of<IRazorCompletionItemProvider>(p => p.GetCompletionItems(context) == ImmutableArray.Create(completionItem2), MockBehavior.Strict);
-        var completionFactsService = new DefaultRazorCompletionFactsService(new[] { provider1, provider2 });
+        var completionFactsService = new RazorCompletionFactsService(new[] { provider1, provider2 });
 
         // Act
         var completionItems = completionFactsService.GetCompletionItems(context);

src/Razor/test/Microsoft.CodeAnalysis.Razor.Workspaces.Test/Completion/DirectiveAttributeParameterCompletionItemProviderTest.cs

@@ -93,7 +93,7 @@ public class DirectiveAttributeParameterCompletionItemProviderTest : RazorIntegr
         var completions = _provider.GetCompletionItems(context);
 
         // Assert
-        Assert.Equal(6, completions.Count);
+        Assert.Equal(6, completions.Length);
         AssertContains(completions, "culture");
         AssertContains(completions, "event");
         AssertContains(completions, "format");

src/Razor/test/Microsoft.VisualStudio.Editor.Razor.Test/Completion/DefaultVisualStudioDescriptionFactoryTest.cs

@@ -23,7 +23,7 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
     public void CreateClassifiedDescription_SingleDescription_NoSeparator()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("TheReturnType", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -33,14 +33,14 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
         var result = factory.CreateClassifiedDescription(description);
 
         // Assert
-        Assert.DoesNotContain(DefaultVisualStudioDescriptionFactory.SeparatorElement, result.Elements);
+        Assert.DoesNotContain(VisualStudioDescriptionFactory.SeparatorElement, result.Elements);
     }
 
     [Fact]
     public void CreateClassifiedDescription_MultipleDescription_Separator()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("TheReturnType", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -51,14 +51,14 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
         var result = factory.CreateClassifiedDescription(description);
 
         // Assert
-        Assert.Contains(DefaultVisualStudioDescriptionFactory.SeparatorElement, result.Elements);
+        Assert.Contains(VisualStudioDescriptionFactory.SeparatorElement, result.Elements);
     }
 
     [Fact]
     public void CreateClassifiedDescription_RepresentsReturnType()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("TheReturnType", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -76,7 +76,7 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
     public void CreateClassifiedDescription_RepresentsTypeName()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("TheReturnType", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -94,7 +94,7 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
     public void CreateClassifiedDescription_RepresentsPropertyName()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("TheReturnType", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -112,7 +112,7 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
     public void CreateClassifiedDescription_RepresentsDocumentation()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("TheReturnType", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -130,7 +130,7 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
     public void CreateClassifiedDescription_CanSimplifyKeywordReturnTypes()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("System.String", "TheTypeName", "ThePropertyName", "The documentation"),
@@ -149,7 +149,7 @@ public class DefaultVisualStudioDescriptionFactoryTest : TestBase
     public void CreateClassifiedDescription_CanRepresentMultipleDescriptions()
     {
         // Arrange
-        var factory = new DefaultVisualStudioDescriptionFactory();
+        var factory = new VisualStudioDescriptionFactory();
         var description = new AggregateBoundAttributeDescription(new[]
         {
             new BoundAttributeDescriptionInfo("System.String", "TheTypeName", "ThePropertyName", "The documentation"),

src/Razor/test/Microsoft.VisualStudio.Editor.Razor.Test/Completion/RazorDirectiveAttributeCompletionSourceTest.cs

@@ -46,11 +46,11 @@ public class RazorDirectiveAttributeCompletionSourceTest : ProjectSnapshotManage
         // Arrange
         var expectedResult = new ContainerElement(ContainerElementStyle.Wrapped);
         var description = new AggregateBoundAttributeDescription(Array.Empty<BoundAttributeDescriptionInfo>());
-        var descriptionFactory = Mock.Of<VisualStudioDescriptionFactory>(factory => factory.CreateClassifiedDescription(description) == expectedResult, MockBehavior.Strict);
+        var descriptionFactory = Mock.Of<IVisualStudioDescriptionFactory>(factory => factory.CreateClassifiedDescription(description) == expectedResult, MockBehavior.Strict);
         var source = new RazorDirectiveAttributeCompletionSource(
             Dispatcher,
             Mock.Of<VisualStudioRazorParser>(MockBehavior.Strict),
-            Mock.Of<RazorCompletionFactsService>(MockBehavior.Strict),
+            Mock.Of<IRazorCompletionFactsService>(MockBehavior.Strict),
             Mock.Of<ICompletionBroker>(MockBehavior.Strict),
             descriptionFactory,
             JoinableTaskFactory);
@@ -240,9 +240,9 @@ public class RazorDirectiveAttributeCompletionSourceTest : ProjectSnapshotManage
         var source = new RazorDirectiveAttributeCompletionSource(
             Dispatcher,
             Mock.Of<VisualStudioRazorParser>(MockBehavior.Strict),
-            Mock.Of<RazorCompletionFactsService>(MockBehavior.Strict),
+            Mock.Of<IRazorCompletionFactsService>(MockBehavior.Strict),
             Mock.Of<ICompletionBroker>(MockBehavior.Strict),
-            Mock.Of<VisualStudioDescriptionFactory>(MockBehavior.Strict),
+            Mock.Of<IVisualStudioDescriptionFactory>(MockBehavior.Strict),
             JoinableTaskFactory);
         return source;
     }

src/Razor/test/Microsoft.VisualStudio.Editor.Razor.Test/Completion/RazorDirectiveCompletionSourceProviderTest.cs

@@ -21,7 +21,7 @@ public class RazorDirectiveCompletionSourceProviderTest : ProjectSnapshotManager
 {
     private readonly IContentType _razorContentType;
     private readonly IContentType _nonRazorContentType;
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
 
     public RazorDirectiveCompletionSourceProviderTest(ITestOutputHelper testOutput)
         : base(testOutput)
@@ -34,7 +34,7 @@ public class RazorDirectiveCompletionSourceProviderTest : ProjectSnapshotManager
             c => c.IsOfType(It.IsAny<string>()) == false,
             MockBehavior.Strict);
 
-        _completionFactsService = Mock.Of<RazorCompletionFactsService>(MockBehavior.Strict);
+        _completionFactsService = Mock.Of<IRazorCompletionFactsService>(MockBehavior.Strict);
     }
 
     [Fact]

src/Razor/test/Microsoft.VisualStudio.Editor.Razor.Test/Completion/RazorDirectiveCompletionSourceTest.cs

@@ -33,12 +33,12 @@ public class RazorDirectiveCompletionSourceTest : ProjectSnapshotManagerDispatch
         CSharpCodeParser.TagHelperPrefixDirectiveDescriptor,
     };
 
-    private readonly RazorCompletionFactsService _completionFactsService;
+    private readonly IRazorCompletionFactsService _completionFactsService;
 
     public RazorDirectiveCompletionSourceTest(ITestOutputHelper testOutput)
         : base(testOutput)
     {
-        _completionFactsService = new DefaultRazorCompletionFactsService(new[] { new DirectiveCompletionItemProvider() });
+        _completionFactsService = new RazorCompletionFactsService(new[] { new DirectiveCompletionItemProvider() });
     }
 
     [UIFact]

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/EnumerableExtensions.cs

@@ -0,0 +1,32 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Collections.Immutable;
+using Microsoft.AspNetCore.Razor.PooledObjects;
+
+namespace System.Collections.Generic;
+
+internal static class EnumerableExtensions
+{
+    public static ImmutableArray<TResult> SelectAsArray<T, TResult>(this IEnumerable<T> source, Func<T, TResult> selector)
+    {
+        if (source is IReadOnlyList<T> list)
+        {
+            return list.SelectAsArray(selector);
+        }
+
+        return BuildResult(source, selector);
+
+        static ImmutableArray<TResult> BuildResult(IEnumerable<T> items, Func<T, TResult> selector)
+        {
+            using var results = new PooledArrayBuilder<TResult>();
+
+            foreach (var item in items)
+            {
+                results.Add(selector(item));
+            }
+
+            return results.DrainToImmutable();
+        }
+    }
+}

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/ImmutableArrayExtensions.cs

@@ -73,15 +73,14 @@ internal static class ImmutableArrayExtensions
 
         static ImmutableArray<TResult> BuildResult(ImmutableArray<T> items, Func<T, TResult> selector)
         {
-            using var _ = ArrayBuilderPool<TResult>.GetPooledObject(out var result);
+            using var results = new PooledArrayBuilder<TResult>(capacity: items.Length);
-            result.SetCapacityIfLarger(items.Length);
 
             foreach (var item in items)
             {
-                result.Add(selector(item));
+                results.Add(selector(item));
             }
 
-            return result.DrainToImmutable();
+            return results.DrainToImmutable();
         }
     }
 }

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/PooledObjects/PooledArrayBuilder`1.cs

@@ -67,6 +67,17 @@ internal ref struct PooledArrayBuilder<T>
         _builder.Add(item);
     }
 
+    public void AddRange(ImmutableArray<T> items)
+    {
+        if (items.Length == 0)
+        {
+            return;
+        }
+
+        _builder ??= GetBuilder();
+        _builder.AddRange(items);
+    }
+
     public void AddRange(IReadOnlyList<T> items)
     {
         if (items.Count == 0)

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/ReadOnlyListExtensions.cs

@@ -0,0 +1,35 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Collections.Immutable;
+using Microsoft.AspNetCore.Razor.PooledObjects;
+
+namespace System.Collections.Generic;
+
+internal static class ReadOnlyListExtensions
+{
+    public static ImmutableArray<TResult> SelectAsArray<T, TResult>(this IReadOnlyList<T> source, Func<T, TResult> selector)
+    {
+        return source switch
+        {
+            [] => ImmutableArray<TResult>.Empty,
+            [var item] => ImmutableArray.Create(selector(item)),
+            [var item1, var item2] => ImmutableArray.Create(selector(item1), selector(item2)),
+            [var item1, var item2, var item3] => ImmutableArray.Create(selector(item1), selector(item2), selector(item3)),
+            [var item1, var item2, var item3, var item4] => ImmutableArray.Create(selector(item1), selector(item2), selector(item3), selector(item4)),
+            var items => BuildResult(items, selector)
+        };
+
+        static ImmutableArray<TResult> BuildResult(IReadOnlyList<T> items, Func<T, TResult> selector)
+        {
+            using var results = new PooledArrayBuilder<TResult>(capacity: items.Count);
+
+            for (var i = 0; i < items.Count; i++)
+            {
+                results.Add(selector(items[i]));
+            }
+
+            return results.DrainToImmutable();
+        }
+    }
+}