Define UnsupportedOSPlatformAttribute

Author: BCSharp

Src/IronPython/SystemRuntimeVersioning.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the Apache 2.0 license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 namespace System.Runtime.Versioning {
 #if !FEATURE_OSPLATFORMATTRIBUTE
     internal abstract class OSPlatformAttribute : Attribute {
@@ -26,5 +28,27 @@ internal sealed class SupportedOSPlatformAttribute : OSPlatformAttribute {
         public SupportedOSPlatformAttribute(string platformName) : base(platformName) {
         }
     }
+
+    [AttributeUsage(AttributeTargets.Assembly |
+                AttributeTargets.Class |
+                AttributeTargets.Constructor |
+                AttributeTargets.Enum |
+                AttributeTargets.Event |
+                AttributeTargets.Field |
+                AttributeTargets.Method |
+                AttributeTargets.Module |
+                AttributeTargets.Property |
+                AttributeTargets.Struct,
+                AllowMultiple = true, Inherited = false)]
+    internal sealed class UnsupportedOSPlatformAttribute : OSPlatformAttribute {
+        public UnsupportedOSPlatformAttribute(string platformName) : base(platformName) {
+        }
+
+        public UnsupportedOSPlatformAttribute (string platformName, string? message) : base(platformName) {
+            Message = message;
+        }
+
+        public string? Message { get; }
+    }
 #endif
 }