Copy AsyncBatchingWorkQueue from Roslyn

Roslyn's `AsyncBatchingWorkQueue` is a battle-hardened utility that provides a robust mechanism to do work in batches without blocking.

eng/Versions.props

@@ -151,6 +151,7 @@
     <NuGetSolutionRestoreManagerInteropVersion>4.8.0</NuGetSolutionRestoreManagerInteropVersion>
     <StreamJsonRpcPackageVersion>2.17.11</StreamJsonRpcPackageVersion>
     <SystemRuntimeInteropServicesRuntimePackageVersion>4.3.0</SystemRuntimeInteropServicesRuntimePackageVersion>
+    <SystemThreadingTasksExtensions>4.5.4</SystemThreadingTasksExtensions>
     <Tooling_MicrosoftCodeAnalysisAnalyzersPackageVersion>3.11.0-beta1.24170.2</Tooling_MicrosoftCodeAnalysisAnalyzersPackageVersion>
     <Tooling_MicrosoftCodeAnalysisBannedApiAnalyzersPackageVersion>$(Tooling_MicrosoftCodeAnalysisAnalyzersPackageVersion)</Tooling_MicrosoftCodeAnalysisBannedApiAnalyzersPackageVersion>
     <Tooling_RoslynDiagnosticsAnalyzersPackageVersion>$(Tooling_MicrosoftCodeAnalysisAnalyzersPackageVersion)</Tooling_RoslynDiagnosticsAnalyzersPackageVersion>

src/Razor/src/Microsoft.AspNetCore.Razor.ExternalAccess.RoslynWorkspace/TaskDelayScheduler.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
+using Microsoft.AspNetCore.Razor.Threading;
+
 namespace Microsoft.AspNetCore.Razor.ExternalAccess.RoslynWorkspace;
 
 // Copied from https://github.com/dotnet/project-system/blob/e4db47666e0a49f6c38e701f8630dbc31380fb64/src/Microsoft.VisualStudio.ProjectSystem.Managed/Threading/Tasks/TaskDelayScheduler.cs

src/Razor/src/Microsoft.AspNetCore.Razor.ProjectEngineHost/Microsoft.AspNetCore.Razor.ProjectEngineHost.csproj

@@ -14,6 +14,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.Workspaces.Common" Version="$(MicrosoftCodeAnalysisWorkspacesCommonPackageVersion)" />
     <PackageReference Include="MessagePack" Version="$(MessagePackPackageVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensions)" />
   </ItemGroup>
 
   <ItemGroup>

src/Razor/src/Microsoft.AspNetCore.Razor.ProjectEngineHost/Threading/CancellationSeries.cs

@@ -1,13 +1,31 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
-namespace Microsoft.AspNetCore.Razor.ExternalAccess.RoslynWorkspace;
+using System;
+using System.Threading;
 
-// Copied from https://github.com/dotnet/project-system/blob/e4db47666e0a49f6c38e701f8630dbc31380fb64/src/Microsoft.VisualStudio.ProjectSystem.Managed/Threading/Tasks/CancellationSeries.cs
+namespace Microsoft.AspNetCore.Razor.Threading;
 
+// NOTE: This code is copied from dotnet/roslyn:
+// https://github.com/dotnet/roslyn/blob/98cd097bf122677378692ebe952b71ab6e5bb013/src/Workspaces/Core/Portable/Utilities/CancellationSeries.cs
+//
+// However, it was originally derived from an implementation in dotnet/project-system:
+// https://github.com/dotnet/project-system/blob/bdf69d5420ec8d894f5bf4c3d4692900b7f2479c/src/Microsoft.VisualStudio.ProjectSystem.Managed/Threading/Tasks/CancellationSeries.cs
+//
+// See the commentary in https://github.com/dotnet/roslyn/pull/50156 for notes on incorporating changes made to the
+// reference implementation.
+
+/// <summary>
+/// Produces a series of <see cref="CancellationToken"/> objects such that requesting a new token
+/// causes the previously issued token to be cancelled.
+/// </summary>
+/// <remarks>
+/// <para>Consuming code is responsible for managing overlapping asynchronous operations.</para>
+/// <para>This class has a lock-free implementation to minimise latency and contention.</para>
+/// </remarks>
 internal sealed class CancellationSeries : IDisposable
 {
-    private CancellationTokenSource? _cts = new();
+    private CancellationTokenSource? _cts;
 
     private readonly CancellationToken _superToken;
 
@@ -16,11 +34,21 @@ internal sealed class CancellationSeries : IDisposable
     /// </summary>
     /// <param name="token">An optional cancellation token that, when cancelled, cancels the last
     /// issued token and causes any subsequent tokens to be issued in a cancelled state.</param>
-    public CancellationSeries(CancellationToken token)
+    public CancellationSeries(CancellationToken token = default)
     {
+        // Initialize with a pre-cancelled source to ensure HasActiveToken has the correct state
+        _cts = new CancellationTokenSource();
+        _cts.Cancel();
+
         _superToken = token;
     }
 
+    /// <summary>
+    /// Determines if the cancellation series has an active token which has not been cancelled.
+    /// </summary>
+    public bool HasActiveToken
+        => _cts is { IsCancellationRequested: false };
+
     /// <summary>
     /// Creates the next <see cref="CancellationToken"/> in the series, ensuring the last issued
     /// token (if any) is cancelled first.
@@ -37,7 +65,7 @@ internal sealed class CancellationSeries : IDisposable
     /// </list>
     /// </returns>
     /// <exception cref="ObjectDisposedException">This object has been disposed.</exception>
-    public CancellationToken CreateNext(CancellationToken token)
+    public CancellationToken CreateNext(CancellationToken token = default)
     {
         var nextSource = CancellationTokenSource.CreateLinkedTokenSource(token, _superToken);
 
@@ -46,9 +74,25 @@ internal sealed class CancellationSeries : IDisposable
         // This way we would return a cancelled token, which is reasonable.
         var nextToken = nextSource.Token;
 
-        var priorSource = Interlocked.Exchange(ref _cts, nextSource);
+        // The following block is identical to Interlocked.Exchange, except no replacement is made if the current
+        // field value is null (latch on null). This ensures state is not corrupted if CreateNext is called after
+        // the object is disposed.
+        var priorSource = Volatile.Read(ref _cts);
+        while (priorSource is not null)
+        {
+            var candidate = Interlocked.CompareExchange(ref _cts, nextSource, priorSource);
 
-        if (priorSource is null)
+            if (candidate == priorSource)
+            {
+                break;
+            }
+            else
+            {
+                priorSource = candidate;
+            }
+        }
+
+        if (priorSource == null)
         {
             nextSource.Dispose();
 
@@ -73,7 +117,7 @@ internal sealed class CancellationSeries : IDisposable
     {
         var source = Interlocked.Exchange(ref _cts, null);
 
-        if (source is null)
+        if (source == null)
         {
             // Already disposed
             return;

src/Razor/src/Microsoft.AspNetCore.Razor.ProjectEngineHost/Threading/TaskExtensions.cs

@@ -0,0 +1,73 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Razor.Threading;
+
+internal static class TaskExtensions
+{
+    /// <summary>
+    /// Asserts the <see cref="Task"/> passed has already been completed.
+    /// </summary>
+    /// <remarks>
+    /// This is useful for a specific case: sometimes you might be calling an API that is "sometimes" async, and you're
+    /// calling it from a synchronous method where you know it should have completed synchronously. This is an easy
+    /// way to assert that while silencing any compiler complaints.
+    /// </remarks>
+    public static void VerifyCompleted(this Task task)
+    {
+        Assumed.True(task.IsCompleted);
+
+        // Propagate any exceptions that may have been thrown.
+        task.GetAwaiter().GetResult();
+    }
+
+    /// <summary>
+    /// Asserts the <see cref="Task"/> passed has already been completed.
+    /// </summary>
+    /// <remarks>
+    /// This is useful for a specific case: sometimes you might be calling an API that is "sometimes" async, and you're
+    /// calling it from a synchronous method where you know it should have completed synchronously. This is an easy
+    /// way to assert that while silencing any compiler complaints.
+    /// </remarks>
+    public static TResult VerifyCompleted<TResult>(this Task<TResult> task)
+    {
+        Assumed.True(task.IsCompleted);
+
+        // Propagate any exceptions that may have been thrown.
+        return task.GetAwaiter().GetResult();
+    }
+
+    /// <summary>
+    /// Asserts the <see cref="ValueTask"/> passed has already been completed.
+    /// </summary>
+    /// <remarks>
+    /// This is useful for a specific case: sometimes you might be calling an API that is "sometimes" async, and you're
+    /// calling it from a synchronous method where you know it should have completed synchronously. This is an easy
+    /// way to assert that while silencing any compiler complaints.
+    /// </remarks>
+    public static void VerifyCompleted(this ValueTask task)
+    {
+        Assumed.True(task.IsCompleted);
+
+        // Propagate any exceptions that may have been thrown.
+        task.GetAwaiter().GetResult();
+    }
+
+    /// <summary>
+    /// Asserts the <see cref="ValueTask"/> passed has already been completed.
+    /// </summary>
+    /// <remarks>
+    /// This is useful for a specific case: sometimes you might be calling an API that is "sometimes" async, and you're
+    /// calling it from a synchronous method where you know it should have completed synchronously. This is an easy
+    /// way to assert that while silencing any compiler complaints.
+    /// </remarks>
+    public static TResult VerifyCompleted<TResult>(this ValueTask<TResult> task)
+    {
+        Assumed.True(task.IsCompleted);
+
+        // Propagate any exceptions that may have been thrown.
+        return task.GetAwaiter().GetResult();
+    }
+}

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Utilities/AsyncBatchingWorkQueue.cs

@@ -0,0 +1,27 @@
+// 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.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor;
+
+namespace Microsoft.CodeAnalysis.Razor.Utilities;
+
+// NOTE: This code is copied and modified slightly from dotnet/roslyn:
+// https://github.com/dotnet/roslyn/blob/98cd097bf122677378692ebe952b71ab6e5bb013/src/Workspaces/Core/Portable/Shared/Utilities/AsyncBatchingWorkQueue%600.cs
+
+/// <inheritdoc cref="AsyncBatchingWorkQueue{TItem, TResult}"/>
+internal class AsyncBatchingWorkQueue(
+    TimeSpan delay,
+    Func<CancellationToken, ValueTask> processBatchAsync,
+    CancellationToken cancellationToken) : AsyncBatchingWorkQueue<VoidResult>(delay, Convert(processBatchAsync), EqualityComparer<VoidResult>.Default, cancellationToken)
+{
+    private static Func<ImmutableArray<VoidResult>, CancellationToken, ValueTask> Convert(Func<CancellationToken, ValueTask> processBatchAsync)
+        => (items, ct) => processBatchAsync(ct);
+
+    public void AddWork(bool cancelExistingWork = false)
+        => base.AddWork(default(VoidResult), cancelExistingWork);
+}

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Utilities/AsyncBatchingWorkQueue`1.cs

@@ -0,0 +1,43 @@
+// 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.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor;
+
+namespace Microsoft.CodeAnalysis.Razor.Utilities;
+
+// NOTE: This code is copied and modified slightly from dotnet/roslyn:
+// https://github.com/dotnet/roslyn/blob/98cd097bf122677378692ebe952b71ab6e5bb013/src/Workspaces/Core/Portable/Shared/Utilities/AsyncBatchingWorkQueue%601.cs
+
+/// <inheritdoc cref="AsyncBatchingWorkQueue{TItem, TResult}"/>
+internal class AsyncBatchingWorkQueue<TItem>(
+    TimeSpan delay,
+    Func<ImmutableArray<TItem>, CancellationToken, ValueTask> processBatchAsync,
+    IEqualityComparer<TItem>? equalityComparer,
+    CancellationToken cancellationToken) : AsyncBatchingWorkQueue<TItem, VoidResult>(delay, Convert(processBatchAsync), equalityComparer, cancellationToken)
+{
+    public AsyncBatchingWorkQueue(
+        TimeSpan delay,
+        Func<ImmutableArray<TItem>, CancellationToken, ValueTask> processBatchAsync,
+        CancellationToken cancellationToken)
+        : this(delay,
+               processBatchAsync,
+               equalityComparer: null,
+               cancellationToken)
+    {
+    }
+
+    private static Func<ImmutableArray<TItem>, CancellationToken, ValueTask<VoidResult>> Convert(Func<ImmutableArray<TItem>, CancellationToken, ValueTask> processBatchAsync)
+        => async (items, ct) =>
+        {
+            await processBatchAsync(items, ct).ConfigureAwait(false);
+            return default;
+        };
+
+    public new Task WaitUntilCurrentBatchCompletesAsync()
+        => base.WaitUntilCurrentBatchCompletesAsync();
+}

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Utilities/AsyncBatchingWorkQueue`2.cs

@@ -0,0 +1,292 @@
+// 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.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Razor.PooledObjects;
+using Microsoft.AspNetCore.Razor.Threading;
+using Microsoft.VisualStudio.Threading;
+
+namespace Microsoft.CodeAnalysis.Razor.Utilities;
+
+// NOTE: This code is derived from dotnet/roslyn:
+// https://github.com/dotnet/roslyn/blob/98cd097bf122677378692ebe952b71ab6e5bb013/src/Workspaces/Core/Portable/Shared/Utilities/AsyncBatchingWorkQueue%602.cs
+
+/// <summary>
+/// A queue where items can be added to to be processed in batches after some delay has passed. When processing
+/// happens, all the items added since the last processing point will be passed along to be worked on.  Rounds of
+/// processing happen serially, only starting up after a previous round has completed.
+/// <para>
+/// Failure to complete a particular batch (either due to cancellation or some faulting error) will not prevent
+/// further batches from executing. The only thing that will permanently stop this queue from processing items is if
+/// the <see cref="CancellationToken"/> passed to the constructor switches to <see
+/// cref="CancellationToken.IsCancellationRequested"/>.
+/// </para>
+/// </summary>
+internal class AsyncBatchingWorkQueue<TItem, TResult>
+{
+    /// <summary>
+    /// Delay we wait after finishing the processing of one batch and starting up on then.
+    /// </summary>
+    private readonly TimeSpan _delay;
+
+    /// <summary>
+    /// Equality comparer uses to dedupe items if present.
+    /// </summary>
+    private readonly IEqualityComparer<TItem>? _equalityComparer;
+
+    /// <summary>
+    /// Callback to actually perform the processing of the next batch of work.
+    /// </summary>
+    private readonly Func<ImmutableArray<TItem>, CancellationToken, ValueTask<TResult>> _processBatchAsync;
+
+    /// <summary>
+    /// Cancellation token controlling the entire queue.  Once this is triggered, we don't want to do any more work
+    /// at all.
+    /// </summary>
+    private readonly CancellationToken _entireQueueCancellationToken;
+
+    /// <summary>
+    /// Cancellation series we use so we can cancel individual batches of work if requested.  The client of the
+    /// queue can cancel existing work by either calling <see cref="CancelExistingWork"/> directly, or passing <see
+    /// langword="true"/> to <see cref="AddWork(TItem, bool)"/>.  Work in the queue that has not started will be
+    /// immediately discarded. The cancellation token passed to <see cref="_processBatchAsync"/> will be triggered
+    /// allowing the client callback to cooperatively cancel the current batch of work it is performing.
+    /// </summary>
+    private readonly CancellationSeries _cancellationSeries;
+
+    #region protected by lock
+
+    /// <summary>
+    /// Lock we will use to ensure the remainder of these fields can be accessed in a thread-safe
+    /// manner.  When work is added we'll place the data into <see cref="_nextBatch"/>.
+    /// We'll then kick of a task to process this in the future if we don't already have an
+    /// existing task in flight for that.
+    /// </summary>
+    private readonly object _gate = new();
+
+    /// <summary>
+    /// Data added that we want to process in our next update task.
+    /// </summary>
+    private readonly ImmutableArray<TItem>.Builder _nextBatch = ImmutableArray.CreateBuilder<TItem>();
+
+    /// <summary>
+    /// CancellationToken controlling the next batch of items to execute.
+    /// </summary>
+    private CancellationToken _nextBatchCancellationToken;
+
+    /// <summary>
+    /// Used if <see cref="_equalityComparer"/> is present to ensure only unique items are added to <see
+    /// cref="_nextBatch"/>.
+    /// </summary>
+    private readonly HashSet<TItem> _uniqueItems;
+
+    /// <summary>
+    /// Task kicked off to do the next batch of processing of <see cref="_nextBatch"/>. These
+    /// tasks form a chain so that the next task only processes when the previous one completes.
+    /// </summary>
+    private Task<TResult?> _updateTask = Task.FromResult(default(TResult));
+
+    /// <summary>
+    /// Whether or not there is an existing task in flight that will process the current batch
+    /// of <see cref="_nextBatch"/>.  If there is an existing in flight task, we don't need to
+    /// kick off a new one if we receive more work before it runs.
+    /// </summary>
+    private bool _taskInFlight = false;
+
+    #endregion
+
+    public AsyncBatchingWorkQueue(
+        TimeSpan delay,
+        Func<ImmutableArray<TItem>, CancellationToken, ValueTask<TResult>> processBatchAsync,
+        IEqualityComparer<TItem>? equalityComparer,
+        CancellationToken cancellationToken)
+    {
+        _delay = delay;
+        _processBatchAsync = processBatchAsync;
+        _equalityComparer = equalityComparer;
+        _entireQueueCancellationToken = cancellationToken;
+
+        _uniqueItems = new HashSet<TItem>(equalityComparer);
+
+        // Combine with the queue cancellation token so that any batch is controlled by that token as well.
+        _cancellationSeries = new CancellationSeries(_entireQueueCancellationToken);
+        CancelExistingWork();
+    }
+
+    /// <summary>
+    /// Cancels any outstanding work in this queue.  Work that has not yet started will never run. Work that is in
+    /// progress will request cancellation in a standard best effort fashion.
+    /// </summary>
+    public void CancelExistingWork()
+    {
+        lock (_gate)
+        {
+            // Cancel out the current executing batch, and create a new token for the next batch.
+            _nextBatchCancellationToken = _cancellationSeries.CreateNext();
+
+            // Clear out the existing items that haven't run yet.  There is no point keeping them around now.
+            _nextBatch.Clear();
+            _uniqueItems.Clear();
+        }
+    }
+
+    public void AddWork(TItem item, bool cancelExistingWork = false)
+    {
+        using var _ = ArrayBuilderPool<TItem>.GetPooledObject(out var items);
+        items.Add(item);
+
+        AddWork(items, cancelExistingWork);
+    }
+
+    public void AddWork(IEnumerable<TItem> items, bool cancelExistingWork = false)
+    {
+        // Don't do any more work if we've been asked to shutdown.
+        if (_entireQueueCancellationToken.IsCancellationRequested)
+        {
+            return;
+        }
+
+        lock (_gate)
+        {
+            // if we were asked to cancel the prior set of items, do so now.
+            if (cancelExistingWork)
+            {
+                CancelExistingWork();
+            }
+
+            // add our work to the set we'll process in the next batch.
+            AddItemsToBatch(items);
+
+            if (!_taskInFlight)
+            {
+                // No in-flight task.  Kick one off to process these messages a second from now.
+                // We always attach the task to the previous one so that notifications to the ui
+                // follow the same order as the notification the OOP server sent to us.
+                _updateTask = ContinueAfterDelayAsync(_updateTask);
+                _taskInFlight = true;
+            }
+        }
+
+        return;
+
+        void AddItemsToBatch(IEnumerable<TItem> items)
+        {
+            // no equality comparer.  We want to process all items.
+            if (_equalityComparer == null)
+            {
+                _nextBatch.AddRange(items);
+                return;
+            }
+
+            // We're deduping items.  Only add the item if it's the first time we've seen it.
+            foreach (var item in items)
+            {
+                if (_uniqueItems.Add(item))
+                {
+                    _nextBatch.Add(item);
+                }
+            }
+        }
+
+        async Task<TResult?> ContinueAfterDelayAsync(Task lastTask)
+        {
+            // Await the previous item in the task chain in a non-throwing fashion.  Regardless of whether that last
+            // task completed successfully or not, we want to move onto the next batch.
+            await lastTask.NoThrowAwaitable(captureContext: false);
+
+            // If we were asked to shutdown, immediately transition to the canceled state without doing any more work.
+            _entireQueueCancellationToken.ThrowIfCancellationRequested();
+
+            // Ensure that we always yield the current thread this is necessary for correctness as we are called
+            // inside a lock that _taskInFlight to true.  We must ensure that the work to process the next batch
+            // must be on another thread that runs afterwards, can only grab the thread once we release it and will
+            // then reset that bool back to false
+            await Task.Yield().ConfigureAwait(false);
+            await Task.Delay(_delay, _entireQueueCancellationToken).ConfigureAwait(false);
+            return await ProcessNextBatchAsync().ConfigureAwait(false);
+        }
+    }
+
+    /// <summary>
+    /// Waits until the current batch of work completes and returns the last value successfully computed from <see
+    /// cref="_processBatchAsync"/>.  If the last <see cref="_processBatchAsync"/> canceled or failed, then a
+    /// corresponding canceled or faulted task will be returned that propagates that outwards.
+    /// </summary>
+    public Task<TResult?> WaitUntilCurrentBatchCompletesAsync()
+    {
+        lock (_gate)
+        {
+#pragma warning disable VSTHRD003 // Avoid awaiting foreign Tasks
+            return _updateTask;
+#pragma warning restore VSTHRD003 // Avoid awaiting foreign Tasks
+        }
+    }
+
+    private async ValueTask<TResult?> ProcessNextBatchAsync()
+    {
+        _entireQueueCancellationToken.ThrowIfCancellationRequested();
+        try
+        {
+            var (nextBatch, batchCancellationToken) = GetNextBatchAndResetQueue();
+
+            // We may have no items if the entire batch was canceled (and no new work was added).
+            if (nextBatch.IsEmpty)
+            {
+                return default;
+            }
+
+            var batchResultTask = _processBatchAsync(nextBatch, batchCancellationToken).Preserve();
+            await batchResultTask.NoThrowAwaitable(false);
+
+            if (batchResultTask.IsCompletedSuccessfully)
+            {
+                // The VS threading library analyzers warn here because we're accessing Result
+                // directly, which can be block. However, this is safe because we've already awaited
+                // the task and verified that it completed successfully.
+#pragma warning disable VSTHRD103
+                return batchResultTask.Result;
+#pragma warning restore VSTHRD103
+            }
+            else if (batchResultTask.IsCanceled && !_entireQueueCancellationToken.IsCancellationRequested)
+            {
+                // Don't bubble up cancellation to the queue for the nested batch cancellation.  Just because we decided
+                // to cancel this batch isn't something that should stop processing further batches.
+                return default;
+            }
+            else
+            {
+                // Realize the completed result to force the exception to be thrown.
+                batchResultTask.VerifyCompleted();
+
+                return Assumed.Unreachable<TResult?>();
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // Silently continue to allow the next batch to be processed.
+        }
+
+        return Assumed.Unreachable<TResult?>();
+    }
+
+    private (ImmutableArray<TItem> items, CancellationToken batchCancellationToken) GetNextBatchAndResetQueue()
+    {
+        lock (_gate)
+        {
+            var nextBatch = _nextBatch.ToImmutable();
+
+            // mark there being no existing update task so that the next OOP notification will
+            // kick one off.
+            _nextBatch.Clear();
+            _uniqueItems.Clear();
+            _taskInFlight = false;
+
+            return (nextBatch, _nextBatchCancellationToken);
+        }
+    }
+}

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

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
@@ -9,14 +10,35 @@ namespace Microsoft.AspNetCore.Razor;
 
 internal static class Assumed
 {
+    public static void False(
+        [DoesNotReturnIf(true)] bool condition,
+        [CallerFilePath] string? path = null,
+        [CallerLineNumber] int line = 0)
+    {
+        if (condition)
+        {
+            ThrowInvalidOperation(SR.Expected_condition_to_be_false, path, line);
+        }
+    }
+
+    public static void True(
+        [DoesNotReturnIf(false)] bool condition,
+        [CallerFilePath] string? path = null,
+        [CallerLineNumber] int line = 0)
+    {
+        if (!condition)
+        {
+            ThrowInvalidOperation(SR.Expected_condition_to_be_true, path, line);
+        }
+    }
+
     /// <summary>
     ///  Can be called at points that are assumed to be unreachable at runtime.
     /// </summary>
     /// <exception cref="InvalidOperationException"/>
     [DoesNotReturn]
     public static void Unreachable([CallerFilePath] string? path = null, [CallerLineNumber] int line = 0)
-        => throw new InvalidOperationException(
-            SR.FormatThis_program_location_is_thought_to_be_unreachable_File_0_Line_1(path, line));
+        => ThrowInvalidOperation(SR.This_program_location_is_thought_to_be_unreachable, path, line);
 
     /// <summary>
     ///  Can be called at points that are assumed to be unreachable at runtime.
@@ -24,6 +46,16 @@ internal static class Assumed
     /// <exception cref="InvalidOperationException"/>
     [DoesNotReturn]
     public static T Unreachable<T>([CallerFilePath] string? path = null, [CallerLineNumber] int line = 0)
-        => throw new InvalidOperationException(
-            SR.FormatThis_program_location_is_thought_to_be_unreachable_File_0_Line_1(path, line));
+    {
+        ThrowInvalidOperation(SR.This_program_location_is_thought_to_be_unreachable, path, line);
+        return default;
+    }
+
+    [DebuggerHidden]
+    [DoesNotReturn]
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void ThrowInvalidOperation(string message, string? path, int line)
+    {
+        throw new InvalidOperationException(message);
+    }
 }

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/SR.resx

@@ -126,11 +126,20 @@
   <data name="Destination_is_too_short" xml:space="preserve">
     <value>Destination is too short.</value>
   </data>
+  <data name="Expected_condition_to_be_false" xml:space="preserve">
+    <value>Expected condition to be false.</value>
+  </data>
+  <data name="Expected_condition_to_be_true" xml:space="preserve">
+    <value>Expected condition to be true.</value>
+  </data>
+  <data name="File_0_Line_1" xml:space="preserve">
+    <value> File='{0}', Line={1}</value>
+  </data>
   <data name="Non_negative_number_required" xml:space="preserve">
     <value>Non-negative number required.</value>
   </data>
-  <data name="This_program_location_is_thought_to_be_unreachable_File_0_Line_1" xml:space="preserve">
-    <value>This program location is thought to be unreachable. File='{0}', Line={1}</value>
+  <data name="This_program_location_is_thought_to_be_unreachable" xml:space="preserve">
+    <value>This program location is thought to be unreachable.</value>
   </data>
   <data name="Unsupported_type_0" xml:space="preserve">
     <value>Unsupported type: '{0}'.</value>

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.cs.xlf

@@ -17,14 +17,29 @@
         <target state="translated">Cíl je příliš krátký.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Vyžaduje se nezáporné číslo.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Toto umístění programu se považuje za nedostupné. File={0}, Line={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.de.xlf

@@ -17,14 +17,29 @@
         <target state="translated">Das Ziel ist zu kurz.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Nicht negative Zahl erforderlich.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Dieser Programmspeicherort wird als nicht erreichbar betrachtet. Datei="{0}", Zeile={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.es.xlf

@@ -17,14 +17,29 @@
         <target state="translated">El destino es demasiado corto.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Se requiere un número no negativo.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Se considera que esta ubicación del programa es inaccesible. Archivo=''{0}'', Línea={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.fr.xlf

@@ -17,14 +17,29 @@
         <target state="translated">La destination est trop courte.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Nombre non négatif obligatoire.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Cet emplacement du programme est considéré comme inaccessible. File='{0}', Ligne={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.it.xlf

@@ -17,14 +17,29 @@
         <target state="translated">La destinazione è troppo breve.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Numero non negativo obbligatorio.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Questo percorso del programma è considerato irraggiungibile. File='{0}', Riga={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.ja.xlf

@@ -17,14 +17,29 @@
         <target state="translated">宛先が短すぎます。</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">負でない数値が必要です。</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">このプログラムの場所には到達できないと考えられます。ファイル='{0}'、行={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.ko.xlf

@@ -17,14 +17,29 @@
         <target state="translated">대상이 너무 짧습니다.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">음수가 아닌 수가 필요합니다.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">이 프로그램 위치에 연결할 수 없는 것으로 간주합니다. File=’{0}’, Line={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.pl.xlf

@@ -17,14 +17,29 @@
         <target state="translated">Miejsce docelowe jest zbyt krótkie.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Wymagana jest liczba nieujemna.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Ta lokalizacja programu jest uważana za nieosiągalną. Plik=„{0}”, Linia={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.pt-BR.xlf

@@ -17,14 +17,29 @@
         <target state="translated">O destino é muito curto.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">É necessário um número não negativo.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Este local do programa é considerado inacessível. Arquivo='{0}', Linha={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.ru.xlf

@@ -17,14 +17,29 @@
         <target state="translated">Имя назначения слишком короткое.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Требуется неотрицательное число.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Похоже, что это расположение программы является недоступным. Файл="{0}", строка={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.tr.xlf

@@ -17,14 +17,29 @@
         <target state="translated">Hedef çok kısa.</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">Negatif olmayan sayı gerekiyor.</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">Bu program konumu erişilemez olarak görülüyor. Dosya='{0}', Satır={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.zh-Hans.xlf

@@ -17,14 +17,29 @@
         <target state="translated">目标太短。</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">需要提供非负数。</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">此程序位置被视为无法访问。File='{0}'，Line={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/Resources/xlf/SR.zh-Hant.xlf

@@ -17,14 +17,29 @@
         <target state="translated">目的地太短。</target>
         <note />
       </trans-unit>
+      <trans-unit id="Expected_condition_to_be_false">
+        <source>Expected condition to be false.</source>
+        <target state="new">Expected condition to be false.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Expected_condition_to_be_true">
+        <source>Expected condition to be true.</source>
+        <target state="new">Expected condition to be true.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="File_0_Line_1">
+        <source> File='{0}', Line={1}</source>
+        <target state="new"> File='{0}', Line={1}</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Non_negative_number_required">
         <source>Non-negative number required.</source>
         <target state="translated">需要非負數。</target>
         <note />
       </trans-unit>
-      <trans-unit id="This_program_location_is_thought_to_be_unreachable_File_0_Line_1">
-        <source>This program location is thought to be unreachable. File='{0}', Line={1}</source>
-        <target state="translated">此程式位置被認為無法連接。File='{0}', Line={1}</target>
+      <trans-unit id="This_program_location_is_thought_to_be_unreachable">
+        <source>This program location is thought to be unreachable.</source>
+        <target state="new">This program location is thought to be unreachable.</target>
         <note />
       </trans-unit>
       <trans-unit id="Unsupported_type_0">

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

@@ -0,0 +1,21 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNetCore.Razor;
+
+/// <summary>
+/// Explicitly indicates result is void
+/// </summary>
+internal readonly struct VoidResult : IEquatable<VoidResult>
+{
+    public override bool Equals(object? obj)
+        => obj is VoidResult;
+
+    public override int GetHashCode()
+        => 0;
+
+    public bool Equals(VoidResult other)
+        => true;
+}