JsonSerializer directly supports immutable arrays.

src/EditorFeatures/CSharpTest/AddUsing/AddUsingTests_NuGet.cs

@@ -258,7 +258,7 @@ public async Task TestFailedInstallRollsBackFile()
         }
 
         private Task<ImmutableArray<PackageWithTypeResult>> CreateSearchResult(
-            string packageName, string typeName, IReadOnlyList<string> containingNamespaceNames)
+            string packageName, string typeName, ImmutableArray<string> containingNamespaceNames)
         {
             return CreateSearchResult(new PackageWithTypeResult(
                 packageName: packageName, typeName: typeName, version: null,
@@ -268,6 +268,6 @@ public async Task TestFailedInstallRollsBackFile()
         private Task<ImmutableArray<PackageWithTypeResult>> CreateSearchResult(params PackageWithTypeResult[] results)
             => Task.FromResult(ImmutableArray.Create(results));
 
-        private IReadOnlyList<string> CreateNameParts(params string[] parts) => parts;
+        private ImmutableArray<string> CreateNameParts(params string[] parts) => parts.ToImmutableArray();
     }
 }
\ No newline at end of file

src/EditorFeatures/Core/SymbolSearch/SymbolSearchUpdateEngineFactory.cs

@@ -124,11 +124,11 @@ private async Task<RemoteHostClient.Session> TryGetSessionAsync()
                     return ImmutableArray<PackageWithTypeResult>.Empty;
                 }
 
-                var results = await session.InvokeAsync<PackageWithTypeResult[]>(
+                var results = await session.InvokeAsync<ImmutableArray<PackageWithTypeResult>>(
                     nameof(IRemoteSymbolSearchUpdateEngine.FindPackagesWithTypeAsync),
                     source, name, arity).ConfigureAwait(false);
 
-                return results.ToImmutableArray();
+                return results;
             }
 
             public async Task<ImmutableArray<PackageWithAssemblyResult>> FindPackagesWithAssemblyAsync(
@@ -141,11 +141,11 @@ private async Task<RemoteHostClient.Session> TryGetSessionAsync()
                     return ImmutableArray<PackageWithAssemblyResult>.Empty;
                 }
 
-                var results = await session.InvokeAsync<PackageWithAssemblyResult[]>(
+                var results = await session.InvokeAsync<ImmutableArray<PackageWithAssemblyResult>>(
                     nameof(IRemoteSymbolSearchUpdateEngine.FindPackagesWithAssemblyAsync),
                     source, assemblyName).ConfigureAwait(false);
 
-                return results.ToImmutableArray();
+                return results;
             }
 
             public async Task<ImmutableArray<ReferenceAssemblyWithTypeResult>> FindReferenceAssembliesWithTypeAsync(
@@ -158,11 +158,11 @@ private async Task<RemoteHostClient.Session> TryGetSessionAsync()
                     return ImmutableArray<ReferenceAssemblyWithTypeResult>.Empty;
                 }
 
-                var results = await session.InvokeAsync<ReferenceAssemblyWithTypeResult[]>(
+                var results = await session.InvokeAsync<ImmutableArray<ReferenceAssemblyWithTypeResult>>(
                     nameof(IRemoteSymbolSearchUpdateEngine.FindReferenceAssembliesWithTypeAsync),
                     name, arity).ConfigureAwait(false);
 
-                return results.ToImmutableArray();
+                return results;
             }
 
             public async Task UpdateContinuouslyAsync(

src/EditorFeatures/VisualBasicTest/Diagnostics/AddImport/AddImportTests_NuGet.vb

@@ -239,7 +239,7 @@ End Class", fixProviderData:=New ProviderData(installerServiceMock.Object, packa
             installerServiceMock.Verify()
         End Function
 
-        Private Function CreateSearchResult(packageName As String, typeName As String, nameParts As IReadOnlyList(Of String)) As Task(Of ImmutableArray(Of PackageWithTypeResult))
+        Private Function CreateSearchResult(packageName As String, typeName As String, nameParts As ImmutableArray(Of String)) As Task(Of ImmutableArray(Of PackageWithTypeResult))
             Return CreateSearchResult(New PackageWithTypeResult(
                 packageName:=packageName,
                 typeName:=typeName,
@@ -252,8 +252,8 @@ End Class", fixProviderData:=New ProviderData(installerServiceMock.Object, packa
             Return Task.FromResult(ImmutableArray.Create(results))
         End Function
 
-        Private Function CreateNameParts(ParamArray parts As String()) As IReadOnlyList(Of String)
-            Return parts
+        Private Function CreateNameParts(ParamArray parts As String()) As ImmutableArray(Of String)
+            Return parts.ToImmutableArray()
         End Function
     End Class
 End Namespace
\ No newline at end of file

src/Features/Core/Portable/DesignerAttributes/IRemoteDesignerAttributeService.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Collections.Immutable;
 using System.Threading.Tasks;
 
 namespace Microsoft.CodeAnalysis.DesignerAttributes
 {
     internal interface IRemoteDesignerAttributeService
     {
-        Task<DesignerAttributeDocumentData[]> ScanDesignerAttributesAsync(ProjectId projectId);
+        Task<ImmutableArray<DesignerAttributeDocumentData>> ScanDesignerAttributesAsync(ProjectId projectId);
     }
-}
+}
\ No newline at end of file

src/Features/Core/Portable/DocumentHighlighting/AbstractDocumentHighlightsService.cs

@@ -48,12 +48,12 @@ internal abstract partial class AbstractDocumentHighlightsService : IDocumentHig
                     return (succeeded: false, ImmutableArray<DocumentHighlights>.Empty);
                 }
 
-                var result = await session.InvokeAsync<SerializableDocumentHighlights[]>(
+                var result = await session.InvokeAsync<ImmutableArray<SerializableDocumentHighlights>>(
                     nameof(IRemoteDocumentHighlights.GetDocumentHighlightsAsync),
                     document.Id,
                     position,
                     documentsToSearch.Select(d => d.Id).ToArray()).ConfigureAwait(false);
-                return (true, SerializableDocumentHighlights.Rehydrate(result, document.Project.Solution));
+                return (true, result.SelectAsArray(h => h.Rehydrate(document.Project.Solution)));
             }
         }
 

src/Features/Core/Portable/DocumentHighlighting/IRemoteDocumentHighlights.cs

@@ -8,47 +8,23 @@ namespace Microsoft.CodeAnalysis.DocumentHighlighting
 {
     internal interface IRemoteDocumentHighlights
     {
-        Task<SerializableDocumentHighlights[]> GetDocumentHighlightsAsync(
+        Task<ImmutableArray<SerializableDocumentHighlights>> GetDocumentHighlightsAsync(
             DocumentId documentId, int position, DocumentId[] documentIdsToSearch);
     }
 
     internal struct SerializableDocumentHighlights
     {
         public DocumentId DocumentId;
-        public HighlightSpan[] HighlightSpans;
+        public ImmutableArray<HighlightSpan> HighlightSpans;
 
-        public static ImmutableArray<DocumentHighlights> Rehydrate(SerializableDocumentHighlights[] array, Solution solution)
-        {
-            var result = ArrayBuilder<DocumentHighlights>.GetInstance(array.Length);
-            foreach (var dehydrated in array)
-            {
-                result.Push(dehydrated.Rehydrate(solution));
-            }
-
-            return result.ToImmutableAndFree();
-        }
-
-        private DocumentHighlights Rehydrate(Solution solution)
+        public DocumentHighlights Rehydrate(Solution solution)
             => new DocumentHighlights(solution.GetDocument(DocumentId), HighlightSpans.ToImmutableArray());
 
-        public static SerializableDocumentHighlights[] Dehydrate(ImmutableArray<DocumentHighlights> array)
-        {
-            var result = new SerializableDocumentHighlights[array.Length];
-            var index = 0;
-            foreach (var highlights in array)
-            {
-                result[index] = Dehydrate(highlights);
-                index++;
-            }
-
-            return result;
-        }
-
-        private static SerializableDocumentHighlights Dehydrate(DocumentHighlights highlights)
+        public static SerializableDocumentHighlights Dehydrate(DocumentHighlights highlights)
             => new SerializableDocumentHighlights
             {
                 DocumentId = highlights.Document.Id,
-                HighlightSpans = highlights.HighlightSpans.ToArray()
+                HighlightSpans = highlights.HighlightSpans
             };
     }
 }
\ No newline at end of file

src/Features/Core/Portable/NavigateTo/AbstractNavigateToSearchService.Remote.cs

@@ -15,23 +15,21 @@ internal abstract partial class AbstractNavigateToSearchService
         private async Task<ImmutableArray<INavigateToSearchResult>> SearchDocumentInRemoteProcessAsync(
             RemoteHostClient.Session session, Document document, string searchPattern, CancellationToken cancellationToken)
         {
-            var serializableResults = await session.InvokeAsync<SerializableNavigateToSearchResult[]>(
+            var serializableResults = await session.InvokeAsync<ImmutableArray<SerializableNavigateToSearchResult>>(
                 nameof(IRemoteNavigateToSearchService.SearchDocumentAsync),
                 new object[] { document.Id, searchPattern }, cancellationToken).ConfigureAwait(false);
 
-            serializableResults = serializableResults ?? Array.Empty<SerializableNavigateToSearchResult>();
-            return serializableResults.Select(r => r.Rehydrate(document.Project.Solution)).ToImmutableArray();
+            return serializableResults.SelectAsArray(r => r.Rehydrate(document.Project.Solution));
         }
 
         private async Task<ImmutableArray<INavigateToSearchResult>> SearchProjectInRemoteProcessAsync(
             RemoteHostClient.Session session, Project project, string searchPattern, CancellationToken cancellationToken)
         {
-            var serializableResults = await session.InvokeAsync<SerializableNavigateToSearchResult[]>(
+            var serializableResults = await session.InvokeAsync<ImmutableArray<SerializableNavigateToSearchResult>>(
                 nameof(IRemoteNavigateToSearchService.SearchProjectAsync),
                 new object[] { project.Id, searchPattern }, cancellationToken).ConfigureAwait(false);
 
-            serializableResults = serializableResults ?? Array.Empty<SerializableNavigateToSearchResult>();
-            return serializableResults.Select(r => r.Rehydrate(project.Solution)).ToImmutableArray();
+            return serializableResults.SelectAsArray(r => r.Rehydrate(project.Solution));
         }
 
         private static Task<RemoteHostClient.Session> GetRemoteHostSessionAsync(Project project, CancellationToken cancellationToken)

src/Features/Core/Portable/NavigateTo/IRemoteNavigateToSearchService.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Collections.Immutable;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Remote;
 
@@ -7,7 +8,7 @@ namespace Microsoft.CodeAnalysis.NavigateTo
 {
     internal interface IRemoteNavigateToSearchService
     {
-        Task<SerializableNavigateToSearchResult[]> SearchDocumentAsync(DocumentId documentId, string searchPattern);
-        Task<SerializableNavigateToSearchResult[]> SearchProjectAsync(ProjectId projectId, string searchPattern);
+        Task<ImmutableArray<SerializableNavigateToSearchResult>> SearchDocumentAsync(DocumentId documentId, string searchPattern);
+        Task<ImmutableArray<SerializableNavigateToSearchResult>> SearchProjectAsync(ProjectId projectId, string searchPattern);
     }
 }

src/Features/Core/Portable/Remote/RemoteArguments.cs

@@ -18,7 +18,7 @@ internal class SerializableNavigateToSearchResult
         public NavigateToMatchKind MatchKind;
         public bool IsCaseSensitive;
         public string Name;
-        public TextSpan[] NameMatchSpans;
+        public ImmutableArray<TextSpan> NameMatchSpans;
         public string SecondarySort;
         public string Summary;
 
@@ -33,7 +33,7 @@ internal static SerializableNavigateToSearchResult Dehydrate(INavigateToSearchRe
                 MatchKind = result.MatchKind,
                 IsCaseSensitive = result.IsCaseSensitive,
                 Name = result.Name,
-                NameMatchSpans = result.NameMatchSpans.ToArray(),
+                NameMatchSpans = result.NameMatchSpans,
                 SecondarySort = result.SecondarySort,
                 Summary = result.Summary,
                 NavigableItem = SerializableNavigableItem.Dehydrate(result.NavigableItem)

src/VisualStudio/Core/Def/Implementation/DesignerAttribute/DesignerAttributeIncrementalAnalyzer.cs

@@ -121,7 +121,7 @@ public async Task AnalyzeProjectAsync(Project project, bool semanticsChanged, In
                     return null;
                 }
 
-                var serializedResults = await session.InvokeAsync<DesignerAttributeDocumentData[]>(
+                var serializedResults = await session.InvokeAsync<ImmutableArray<DesignerAttributeDocumentData>>(
                     nameof(IRemoteDesignerAttributeService.ScanDesignerAttributesAsync), project.Id).ConfigureAwait(false);
 
                 var data = serializedResults.ToImmutableDictionary(kvp => kvp.FilePath);

src/VisualStudio/Core/Test.Next/Services/ServiceHubServicesTests.cs

@@ -93,7 +93,7 @@ class Test { }";
 
                 var solution = workspace.CurrentSolution;
 
-                var result = await client.RunCodeAnalysisServiceOnRemoteHostAsync<DesignerAttributeDocumentData[]>(
+                var result = await client.RunCodeAnalysisServiceOnRemoteHostAsync<ImmutableArray<DesignerAttributeDocumentData>>(
                     solution, nameof(IRemoteDesignerAttributeService.ScanDesignerAttributesAsync),
                     solution.Projects.First().Id, CancellationToken.None);
 

src/Workspaces/Core/Portable/FindSymbols/Declarations/DeclarationFinder_AllDeclarations.cs

@@ -98,7 +98,7 @@ internal static partial class DeclarationFinder
             {
                 if (session != null)
                 {
-                    var result = await session.InvokeAsync<SerializableSymbolAndProjectId[]>(
+                    var result = await session.InvokeAsync<ImmutableArray<SerializableSymbolAndProjectId>>(
                         nameof(IRemoteSymbolFinder.FindAllDeclarationsWithNormalQueryAsync),
                         project.Id, query.Name, query.Kind, criteria).ConfigureAwait(false);
 
@@ -113,7 +113,7 @@ internal static partial class DeclarationFinder
         }
 
         private static async Task<ImmutableArray<SymbolAndProjectId>> RehydrateAsync(
-            Solution solution, SerializableSymbolAndProjectId[] array, CancellationToken cancellationToken)
+            Solution solution, ImmutableArray<SerializableSymbolAndProjectId> array, CancellationToken cancellationToken)
         {
             var result = ArrayBuilder<SymbolAndProjectId>.GetInstance(array.Length);
 

src/Workspaces/Core/Portable/FindSymbols/Declarations/DeclarationFinder_SourceDeclarations.cs

@@ -118,7 +118,7 @@ internal static partial class DeclarationFinder
             {
                 if (session != null)
                 {
-                    var result = await session.InvokeAsync<SerializableSymbolAndProjectId[]>(
+                    var result = await session.InvokeAsync<ImmutableArray<SerializableSymbolAndProjectId>>(
                         nameof(IRemoteSymbolFinder.FindSolutionSourceDeclarationsWithNormalQueryAsync),
                         name, ignoreCase, criteria).ConfigureAwait(false);
 
@@ -139,7 +139,7 @@ internal static partial class DeclarationFinder
             {
                 if (session != null)
                 {
-                    var result = await session.InvokeAsync<SerializableSymbolAndProjectId[]>(
+                    var result = await session.InvokeAsync<ImmutableArray<SerializableSymbolAndProjectId>>(
                         nameof(IRemoteSymbolFinder.FindProjectSourceDeclarationsWithNormalQueryAsync),
                         project.Id, name, ignoreCase, criteria).ConfigureAwait(false);
 
@@ -160,7 +160,7 @@ internal static partial class DeclarationFinder
             {
                 if (session != null)
                 {
-                    var result = await session.InvokeAsync<SerializableSymbolAndProjectId[]>(
+                    var result = await session.InvokeAsync<ImmutableArray<SerializableSymbolAndProjectId>>(
                         nameof(IRemoteSymbolFinder.FindProjectSourceDeclarationsWithPatternAsync),
                         project.Id, pattern, criteria).ConfigureAwait(false);
 

src/Workspaces/Core/Portable/FindSymbols/IRemoteSymbolFinder.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Collections.Immutable;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Remote;
 
@@ -10,16 +11,16 @@ internal interface IRemoteSymbolFinder
         Task FindReferencesAsync(SerializableSymbolAndProjectId symbolAndProjectIdArg, DocumentId[] documentArgs);
         Task FindLiteralReferencesAsync(object value);
 
-        Task<SerializableSymbolAndProjectId[]> FindAllDeclarationsWithNormalQueryAsync(
+        Task<ImmutableArray<SerializableSymbolAndProjectId>> FindAllDeclarationsWithNormalQueryAsync(
             ProjectId projectId, string name, SearchKind searchKind, SymbolFilter criteria);
 
-        Task<SerializableSymbolAndProjectId[]> FindSolutionSourceDeclarationsWithNormalQueryAsync(
+        Task<ImmutableArray<SerializableSymbolAndProjectId>> FindSolutionSourceDeclarationsWithNormalQueryAsync(
             string name, bool ignoreCase, SymbolFilter criteria);
 
-        Task<SerializableSymbolAndProjectId[]> FindProjectSourceDeclarationsWithNormalQueryAsync(
+        Task<ImmutableArray<SerializableSymbolAndProjectId>> FindProjectSourceDeclarationsWithNormalQueryAsync(
             ProjectId projectId, string name, bool ignoreCase, SymbolFilter criteria);
 
-        Task<SerializableSymbolAndProjectId[]> FindProjectSourceDeclarationsWithPatternAsync(
+        Task<ImmutableArray<SerializableSymbolAndProjectId>> FindProjectSourceDeclarationsWithPatternAsync(
             ProjectId projectId, string pattern, SymbolFilter criteria);
     }
 }
\ No newline at end of file

src/Workspaces/Core/Portable/SymbolSearch/IRemoteSymbolSearchUpdateEngine.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Collections.Immutable;
 using System.Threading.Tasks;
 
 namespace Microsoft.CodeAnalysis.SymbolSearch
@@ -8,8 +9,8 @@ internal interface IRemoteSymbolSearchUpdateEngine
     {
         Task UpdateContinuouslyAsync(string sourceName, string localSettingsDirectory);
 
-        Task<PackageWithTypeResult[]> FindPackagesWithTypeAsync(string source, string name, int arity);
-        Task<PackageWithAssemblyResult[]> FindPackagesWithAssemblyAsync(string source, string name);
-        Task<ReferenceAssemblyWithTypeResult[]> FindReferenceAssembliesWithTypeAsync(string name, int arity);
+        Task<ImmutableArray<PackageWithTypeResult>> FindPackagesWithTypeAsync(string source, string name, int arity);
+        Task<ImmutableArray<PackageWithAssemblyResult>> FindPackagesWithAssemblyAsync(string source, string name);
+        Task<ImmutableArray<ReferenceAssemblyWithTypeResult>> FindReferenceAssembliesWithTypeAsync(string name, int arity);
     }
 }
\ No newline at end of file

src/Workspaces/Remote/ServiceHub/Services/CodeAnalysisService_DesignerAttributes.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.DesignerAttributes;
@@ -16,7 +17,7 @@ internal partial class CodeAnalysisService : IRemoteDesignerAttributeService
         /// 
         /// This will be called by ServiceHub/JsonRpc framework
         /// </summary>
-        public async Task<DesignerAttributeDocumentData[]> ScanDesignerAttributesAsync(ProjectId projectId)
+        public async Task<ImmutableArray<DesignerAttributeDocumentData>> ScanDesignerAttributesAsync(ProjectId projectId)
         {
             using (RoslynLogger.LogBlock(FunctionId.CodeAnalysisService_GetDesignerAttributesAsync, projectId.DebugName, CancellationToken))
             {
@@ -25,7 +26,7 @@ public async Task<DesignerAttributeDocumentData[]> ScanDesignerAttributesAsync(P
                 var data = await AbstractDesignerAttributeService.TryAnalyzeProjectInCurrentProcessAsync(
                     project, CancellationToken).ConfigureAwait(false);
 
-                return data.Values.ToArray();
+                return data.Values.ToImmutableArray();
             }
         }
     }

src/Workspaces/Remote/ServiceHub/Services/CodeAnalysisService_DocumentHighlights.cs

@@ -11,7 +11,7 @@ namespace Microsoft.CodeAnalysis.Remote
     // root level service for all Roslyn services
     internal partial class CodeAnalysisService : IRemoteDocumentHighlights
     {
-        public async Task<SerializableDocumentHighlights[]> GetDocumentHighlightsAsync(
+        public async Task<ImmutableArray<SerializableDocumentHighlights>> GetDocumentHighlightsAsync(
             DocumentId documentId, int position, DocumentId[] documentIdsToSearch)
         {
             var solution = await GetSolutionAsync().ConfigureAwait(false);
@@ -22,7 +22,7 @@ internal partial class CodeAnalysisService : IRemoteDocumentHighlights
             var result = await service.GetDocumentHighlightsAsync(
                 document, position, documentsToSearch, CancellationToken).ConfigureAwait(false);
 
-            return SerializableDocumentHighlights.Dehydrate(result);
+            return result.SelectAsArray(SerializableDocumentHighlights.Dehydrate);
         }
     }
 }
\ No newline at end of file

src/Workspaces/Remote/ServiceHub/Services/CodeAnalysisService_NavigateTo.cs

@@ -9,7 +9,7 @@ namespace Microsoft.CodeAnalysis.Remote
 {
     internal partial class CodeAnalysisService : IRemoteNavigateToSearchService
     {
-        public async Task<SerializableNavigateToSearchResult[]> SearchDocumentAsync(
+        public async Task<ImmutableArray<SerializableNavigateToSearchResult>> SearchDocumentAsync(
             DocumentId documentId, string searchPattern)
         {
             using (UserOperationBooster.Boost())
@@ -24,7 +24,7 @@ internal partial class CodeAnalysisService : IRemoteNavigateToSearchService
             }
         }
 
-        public async Task<SerializableNavigateToSearchResult[]> SearchProjectAsync(
+        public async Task<ImmutableArray<SerializableNavigateToSearchResult>> SearchProjectAsync(
             ProjectId projectId, string searchPattern)
         {
             using (UserOperationBooster.Boost())
@@ -39,10 +39,10 @@ internal partial class CodeAnalysisService : IRemoteNavigateToSearchService
             }
         }
 
-        private SerializableNavigateToSearchResult[] Convert(
+        private ImmutableArray<SerializableNavigateToSearchResult> Convert(
             ImmutableArray<INavigateToSearchResult> result)
         {
-            return result.Select(SerializableNavigateToSearchResult.Dehydrate).ToArray();
+            return result.SelectAsArray(SerializableNavigateToSearchResult.Dehydrate);
         }
     }
 }
\ No newline at end of file

src/Workspaces/Remote/ServiceHub/Services/CodeAnalysisService_SymbolFinder.cs

@@ -44,7 +44,7 @@ public async Task FindLiteralReferencesAsync(object value)
                 value, solution, progressCallback, CancellationToken).ConfigureAwait(false);
         }
 
-        public async Task<SerializableSymbolAndProjectId[]> FindAllDeclarationsWithNormalQueryAsync(
+        public async Task<ImmutableArray<SerializableSymbolAndProjectId>> FindAllDeclarationsWithNormalQueryAsync(
             ProjectId projectId, string name, SearchKind searchKind, SymbolFilter criteria)
         {
             var solution = await GetSolutionAsync().ConfigureAwait(false);
@@ -55,21 +55,21 @@ public async Task FindLiteralReferencesAsync(object value)
                 var result = await DeclarationFinder.FindAllDeclarationsWithNormalQueryInCurrentProcessAsync(
                     project, query, criteria, this.CancellationToken).ConfigureAwait(false);
 
-                return result.Select(SerializableSymbolAndProjectId.Dehydrate).ToArray();
+                return result.SelectAsArray(SerializableSymbolAndProjectId.Dehydrate);
             }
         }
 
-        public async Task<SerializableSymbolAndProjectId[]> FindSolutionSourceDeclarationsWithNormalQueryAsync(
+        public async Task<ImmutableArray<SerializableSymbolAndProjectId>> FindSolutionSourceDeclarationsWithNormalQueryAsync(
             string name, bool ignoreCase, SymbolFilter criteria)
         {
             var solution = await GetSolutionAsync().ConfigureAwait(false);
             var result = await DeclarationFinder.FindSourceDeclarationsWithNormalQueryInCurrentProcessAsync(
                 solution, name, ignoreCase, criteria, CancellationToken).ConfigureAwait(false);
 
-            return result.Select(SerializableSymbolAndProjectId.Dehydrate).ToArray();
+            return result.SelectAsArray(SerializableSymbolAndProjectId.Dehydrate);
         }
 
-        public async Task<SerializableSymbolAndProjectId[]> FindProjectSourceDeclarationsWithNormalQueryAsync(
+        public async Task<ImmutableArray<SerializableSymbolAndProjectId>> FindProjectSourceDeclarationsWithNormalQueryAsync(
             ProjectId projectId, string name, bool ignoreCase, SymbolFilter criteria)
         {
             var solution = await GetSolutionAsync().ConfigureAwait(false);
@@ -78,10 +78,10 @@ public async Task FindLiteralReferencesAsync(object value)
             var result = await DeclarationFinder.FindSourceDeclarationsWithNormalQueryInCurrentProcessAsync(
                 project, name, ignoreCase, criteria, CancellationToken).ConfigureAwait(false);
 
-            return result.Select(SerializableSymbolAndProjectId.Dehydrate).ToArray();
+            return result.SelectAsArray(SerializableSymbolAndProjectId.Dehydrate);
         }
 
-        public async Task<SerializableSymbolAndProjectId[]> FindProjectSourceDeclarationsWithPatternAsync(
+        public async Task<ImmutableArray<SerializableSymbolAndProjectId>> FindProjectSourceDeclarationsWithPatternAsync(
             ProjectId projectId, string pattern, SymbolFilter criteria)
         {
             var solution = await GetSolutionAsync().ConfigureAwait(false);
@@ -90,7 +90,7 @@ public async Task FindLiteralReferencesAsync(object value)
             var result = await DeclarationFinder.FindSourceDeclarationsWithPatternInCurrentProcessAsync(
                 project, pattern, criteria, CancellationToken).ConfigureAwait(false);
 
-            return result.Select(SerializableSymbolAndProjectId.Dehydrate).ToArray();
+            return result.SelectAsArray(SerializableSymbolAndProjectId.Dehydrate);
         }
 
         private class FindLiteralReferencesProgressCallback : IStreamingFindLiteralReferencesProgress

src/Workspaces/Remote/ServiceHub/Services/RemoteSymbolSearchUpdateEngine.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Immutable;
 using System.IO;
-using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.SymbolSearch;
 
@@ -26,28 +26,28 @@ public Task UpdateContinuouslyAsync(string sourceName, string localSettingsDirec
             return _updateEngine.UpdateContinuouslyAsync(sourceName, localSettingsDirectory);
         }
 
-        public async Task<PackageWithTypeResult[]> FindPackagesWithTypeAsync(string source, string name, int arity)
+        public async Task<ImmutableArray<PackageWithTypeResult>> FindPackagesWithTypeAsync(string source, string name, int arity)
         {
             var results = await _updateEngine.FindPackagesWithTypeAsync(
                 source, name, arity).ConfigureAwait(false);
-            var serializedResults = results.ToArray();
-            return serializedResults;
+
+            return results;
         }
 
-        public async Task<PackageWithAssemblyResult[]> FindPackagesWithAssemblyAsync(string source, string assemblyName)
+        public async Task<ImmutableArray<PackageWithAssemblyResult>> FindPackagesWithAssemblyAsync(string source, string assemblyName)
         {
             var results = await _updateEngine.FindPackagesWithAssemblyAsync(
                 source, assemblyName).ConfigureAwait(false);
-            var serializedResults = results.ToArray();
-            return serializedResults;
+
+            return results;
         }
 
-        public async Task<ReferenceAssemblyWithTypeResult[]> FindReferenceAssembliesWithTypeAsync(string name, int arity)
+        public async Task<ImmutableArray<ReferenceAssemblyWithTypeResult>> FindReferenceAssembliesWithTypeAsync(string name, int arity)
         {
             var results = await _updateEngine.FindReferenceAssembliesWithTypeAsync(
                 name, arity).ConfigureAwait(false);
-            var serializedResults = results.ToArray();
-            return serializedResults;
+
+            return results;
         }
 
         private class LogService : ISymbolSearchLogService