Policyfill UnscopedRef

Author: stefannikolei

src/ImageSharp/Diagnostics/CodeAnalysis/UnscopedRefAttribute.cs

@@ -0,0 +1,42 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+#if NET6_0
+// 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>
+    /// Used to indicate a byref escapes and is not scoped.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// There are several cases where the C# compiler treats a <see langword="ref"/> as implicitly
+    /// <see langword="scoped"/> - where the compiler does not allow the <see langword="ref"/> to escape the method.
+    /// </para>
+    /// <para>
+    /// For example:
+    /// <list type="number">
+    ///     <item><see langword="this"/> for <see langword="struct"/> instance methods.</item>
+    ///     <item><see langword="ref"/> parameters that refer to <see langword="ref"/> <see langword="struct"/> types.</item>
+    ///     <item><see langword="out"/> parameters.</item>
+    /// </list>
+    /// </para>
+    /// <para>
+    /// This attribute is used in those instances where the <see langword="ref"/> should be allowed to escape.
+    /// </para>
+    /// <para>
+    /// Applying this attribute, in any form, has impact on consumers of the applicable API. It is necessary for
+    /// API authors to understand the lifetime implications of applying this attribute and how it may impact their users.
+    /// </para>
+    /// </remarks>
+    [global::System.AttributeUsage(
+        global::System.AttributeTargets.Method |
+        global::System.AttributeTargets.Property |
+        global::System.AttributeTargets.Parameter,
+        AllowMultiple = false,
+        Inherited = false)]
+    internal sealed class UnscopedRefAttribute : global::System.Attribute
+    {
+    }
+}
+#endif

src/ImageSharp/Primitives/ColorMatrix.Impl.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-#if NET7_0_OR_GREATER
 #pragma warning disable SA1117 // Parameters should be on same line or separate lines
 using System.Diagnostics.CodeAnalysis;
 using System.Numerics;
@@ -205,5 +204,3 @@ public readonly bool Equals(in Impl other) =>
         public override readonly int GetHashCode() => HashCode.Combine(this.X, this.Y, this.Z, this.W, this.V);
     }
 }
-#endif
-