Add [ConstantExpected] polyfill

README.md

@@ -54,6 +54,7 @@ Here's an example of some of the new features that **PolySharp** can enable down
 - `[Experimental]` (needed for [experimental features](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-12.0/experimental-attribute))
 - `[OverloadResolutionPriority]` (needed for [overload resolution priority](https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13#overload-resolution-priority))
 - `[ParamsCollection]` (needed for [params collection](https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13#params-collections))
+- `[ConstantExpected]` (see [proposal](https://github.com/dotnet/runtime/issues/33771))
 
 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>13.0</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.Package/README.md

@@ -52,6 +52,7 @@ Here's an example of some of the new features that **PolySharp** can enable down
 - `[Experimental]` (needed for [experimental features](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-12.0/experimental-attribute))
 - `[OverloadResolutionPriority]` (needed for [overload resolution priority](https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13#overload-resolution-priority))
 - `[ParamsCollection]` (needed for [params collection](https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13#params-collections))
+- `[ConstantExpected]` (see [proposal](https://github.com/dotnet/runtime/issues/33771))
 
 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>13.0</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.Diagnostics.CodeAnalysis.ConstantExpectedAttribute.cs

@@ -0,0 +1,30 @@
+// <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.Diagnostics.CodeAnalysis
+{
+    /// <summary>
+    /// Indicates that the specified method parameter expects a constant.
+    /// </summary>
+    /// <remarks>
+    /// This can be used to inform tooling that a constant should be used as an argument for the annotated parameter.
+    /// </remarks>
+    [global::System.AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
+    [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+    internal sealed class ConstantExpectedAttribute : global::System.Attribute
+    {
+        /// <summary>
+        /// Indicates the minimum bound of the expected constant, inclusive.
+        /// </summary>
+        public object? Min { get; set; }
+
+        /// <summary>
+        /// Indicates the maximum bound of the expected constant, inclusive.
+        /// </summary>
+        public object? Max { get; set; }
+    }
+}

tests/PolySharp.Tests/LanguageFeatures.cs

@@ -285,4 +285,15 @@ public static void TestOverload(int x)
     public static void TestOverload(int x, int y = 0)
     {
     }
-}
+}
+
+internal static class ConstantExpectedTests
+{
+    public static void CpuIntrinsic([ConstantExpected] int value)
+    {
+    }
+
+    public static void AnotherCpuIntrinsic([ConstantExpected(Min = 0, Max = 8)] int value)
+    {
+    }
+}