Add [RequiresPreviewFeatures] to unsafe APIs

CommunityToolkit.HighPerformance/Extensions/SpinLockExtensions.cs

@@ -4,6 +4,7 @@
 
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
 using System.Threading;
 
 namespace CommunityToolkit.HighPerformance;
@@ -94,6 +95,9 @@ public void Dispose()
     /// <param name="spinLock">The target <see cref="SpinLock"/> to use</param>
     /// <returns>A wrapper type that will release <paramref name="spinLock"/> when its <see cref="System.IDisposable.Dispose"/> method is called.</returns>
     /// <remarks>The returned <see cref="Lock"/> value shouldn't be used directly: use this extension in a <see langword="using"/> block or statement.</remarks>
+    [RequiresPreviewFeatures(
+        "The Lock type has no compiler support to ensure the lifetime of referenced values is respected, and as such using it incorrectly may lead to GC holes.",
+        Url = "https://github.com/dotnet/runtime/issues/46104")]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static Lock Enter(ref this SpinLock spinLock)
     {
@@ -131,6 +135,9 @@ public static Lock Enter(object owner, ref SpinLock spinLock)
     /// A <see langword="struct"/> that is used to enter and hold a <see cref="SpinLock"/> through a <see langword="using"/> block or statement.
     /// </summary>
     [EditorBrowsable(EditorBrowsableState.Never)]
+    [RequiresPreviewFeatures(
+        "The Lock type has no compiler support to ensure the lifetime of referenced values is respected, and as such using it incorrectly may lead to GC holes.",
+        Url = "https://github.com/dotnet/runtime/issues/46104")]
     public readonly ref struct Lock
     {
         /// <summary>

CommunityToolkit.HighPerformance/NullableReadOnlyRef{T}.cs

@@ -7,6 +7,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
 
 namespace CommunityToolkit.HighPerformance;
 
@@ -14,6 +15,9 @@ namespace CommunityToolkit.HighPerformance;
 /// A <see langword="struct"/> that can store an optional readonly reference to a value of a specified type.
 /// </summary>
 /// <typeparam name="T">The type of value to reference.</typeparam>
+[RequiresPreviewFeatures(
+    "The NullableReadOnlyRef<T> type has no compiler support to ensure the lifetime of referenced values is respected, and as such using it incorrectly may lead to GC holes.",
+    Url = "https://github.com/dotnet/runtime/issues/46104")]
 public readonly ref struct NullableReadOnlyRef<T>
 {
     /// <summary>

CommunityToolkit.HighPerformance/NullableRef{T}.cs

@@ -7,6 +7,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
 
 namespace CommunityToolkit.HighPerformance;
 
@@ -14,6 +15,9 @@ namespace CommunityToolkit.HighPerformance;
 /// A <see langword="struct"/> that can store an optional reference to a value of a specified type.
 /// </summary>
 /// <typeparam name="T">The type of value to reference.</typeparam>
+[RequiresPreviewFeatures(
+    "The NullableRef<T> type has no compiler support to ensure the lifetime of referenced values is respected, and as such using it incorrectly may lead to GC holes.",
+    Url = "https://github.com/dotnet/runtime/issues/46104")]
 public readonly ref struct NullableRef<T>
 {
     /// <summary>

CommunityToolkit.HighPerformance/Properties/Polyfills/RequiresPreviewFeaturesAttribute.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#if !NET6_0_OR_GREATER
+
+namespace System.Runtime.Versioning;
+
+/// <summary>
+/// Indicates that an API is in preview.
+/// </summary>
+[AttributeUsage(
+    AttributeTargets.Assembly |
+    AttributeTargets.Module |
+    AttributeTargets.Class |
+    AttributeTargets.Interface |
+    AttributeTargets.Delegate |
+    AttributeTargets.Struct |
+    AttributeTargets.Enum |
+    AttributeTargets.Constructor |
+    AttributeTargets.Method |
+    AttributeTargets.Property |
+    AttributeTargets.Field |
+    AttributeTargets.Event,
+    Inherited = false)]
+internal sealed class RequiresPreviewFeaturesAttribute : Attribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <seealso cref="RequiresPreviewFeaturesAttribute"/> class.
+    /// </summary>
+    public RequiresPreviewFeaturesAttribute()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <seealso cref="RequiresPreviewFeaturesAttribute"/> class with the specified message.
+    /// </summary>
+    /// <param name="message">An optional message associated with this attribute instance.</param>
+    public RequiresPreviewFeaturesAttribute(string? message)
+    {
+        Message = message;
+    }
+
+    /// <summary>
+    /// Returns the optional message associated with this attribute instance.
+    /// </summary>
+    public string? Message { get; }
+
+    /// <summary>
+    /// Returns the optional URL associated with this attribute instance.
+    /// </summary>
+    public string? Url { get; set; }
+}
+
+#endif

CommunityToolkit.HighPerformance/ReadOnlyRef{T}.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
 #if NETSTANDARD2_1_OR_GREATER
 using System.Runtime.InteropServices;
 #else
@@ -16,6 +17,9 @@ namespace CommunityToolkit.HighPerformance;
 /// A <see langword="struct"/> that can store a readonly reference to a value of a specified type.
 /// </summary>
 /// <typeparam name="T">The type of value to reference.</typeparam>
+[RequiresPreviewFeatures(
+    "The ReadOnlyRef<T> type has no compiler support to ensure the lifetime of referenced values is respected, and as such using it incorrectly may lead to GC holes.",
+    Url = "https://github.com/dotnet/runtime/issues/46104")]
 public readonly ref struct ReadOnlyRef<T>
 {
 #if NETSTANDARD2_1_OR_GREATER

CommunityToolkit.HighPerformance/Ref{T}.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
 #if NETSTANDARD2_1_OR_GREATER
 using System.Runtime.InteropServices;
 #else
@@ -16,6 +17,9 @@ namespace CommunityToolkit.HighPerformance;
 /// A <see langword="struct"/> that can store a reference to a value of a specified type.
 /// </summary>
 /// <typeparam name="T">The type of value to reference.</typeparam>
+[RequiresPreviewFeatures(
+    "The Ref<T> type has no compiler support to ensure the lifetime of referenced values is respected, and as such using it incorrectly may lead to GC holes.",
+    Url = "https://github.com/dotnet/runtime/issues/46104")]
 public readonly ref struct Ref<T>
 {
 #if NETSTANDARD2_1_OR_GREATER

tests/CommunityToolkit.HighPerformance.UnitTests/CommunityToolkit.HighPerformance.UnitTests.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>net472;netcoreapp3.1;net6.0</TargetFrameworks>
+    <EnablePreviewFeatures>true</EnablePreviewFeatures>
   </PropertyGroup>
 
   <ItemGroup>