Add [RequiresPreviewFeatures] polyfill

README.md

@@ -32,6 +32,7 @@
   - `[InterpolatedStringHandler]`
   - `[InterpolatedStringHandlerArgument]`
 - `[CallerArgumentExpression]` (see [docs](https://learn.microsoft.com/dotnet/csharp/language-reference/proposals/csharp-10.0/caller-argument-expression))
+- `[RequiresPreviewFeatures]` (needed for [preview features](https://github.com/dotnet/designs/blob/main/accepted/2021/preview-features/preview-features.md))
 
 To leverage them, make sure to bump your C# language version. You can do this by setting the `<LangVersion>` MSBuild property in your project. For instance, by adding `<LangVersion>11.0</LangVersion>` (or your desired C# version) to the first `<PropertyGroup>` of your .csproj file. For more info on this, [see here](https://sergiopedri.medium.com/enabling-and-using-c-9-features-on-older-and-unsupported-runtimes-ce384d8debb), but remember that you don't need to manually copy polyfills anymore: simply adding a reference to **PolySharp** will do this for you automatically.
 

src/PolySharp.SourceGenerators/EmbeddedResources/System.Runtime.Versioning.RequiresPreviewFeaturesAttribute.cs

@@ -0,0 +1,48 @@
+// <auto-generated/>
+#pragma warning disable
+#nullable enable annotations
+
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Runtime.Versioning
+{
+    [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 <see cref="RequiresPreviewFeaturesAttribute"/> class.
+        /// </summary>
+        public RequiresPreviewFeaturesAttribute() { }
+
+        /// <summary>
+        /// Initializes a new instance of the <see 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; }
+    }
+}

tests/PolySharp.Tests/LanguageFeatures.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
 
 namespace PolySharp.Tests;
 
@@ -81,6 +82,11 @@ public bool TakeValue([NotNullWhen(true)] out string? value)
 
         return true;
     }
+
+    [RequiresPreviewFeatures]
+    public void PreviewApi()
+    {
+    }
 }
 
 internal class TestClassWithRequiredMembers