Add RemoveCompilerFeatureRequiredAttribute

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -1406,6 +1406,7 @@ namespace ICSharpCode.Decompiler.CSharp
 								attr.Remove();
 						}
 					}
+					RemoveCompilerFeatureRequiredAttribute(typeDecl, "RefStructs");
 				}
 				if (settings.RequiredMembers)
 				{
@@ -1851,6 +1852,30 @@ namespace ICSharpCode.Decompiler.CSharp
 			return found;
 		}
 
+		internal static bool RemoveCompilerFeatureRequiredAttribute(EntityDeclaration entityDecl, string feature)
+		{
+			bool found = false;
+			foreach (var section in entityDecl.Attributes)
+			{
+				foreach (var attr in section.Attributes)
+				{
+					var symbol = attr.Type.GetSymbol();
+					if (symbol is ITypeDefinition td && td.FullTypeName == KnownAttribute.CompilerFeatureRequired.GetTypeName()
+						&& attr.Arguments.Count == 1 && attr.Arguments.SingleOrDefault() is PrimitiveExpression pe
+						&& pe.Value is string s && s == feature)
+					{
+						attr.Remove();
+						found = true;
+					}
+				}
+				if (section.Attributes.Count == 0)
+				{
+					section.Remove();
+				}
+			}
+			return found;
+		}
+
 		bool FindAttribute(EntityDeclaration entityDecl, KnownAttribute attributeType, out Syntax.Attribute attribute)
 		{
 			attribute = null;

ICSharpCode.Decompiler/TypeSystem/Implementation/KnownAttributes.cs

@@ -33,6 +33,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		None,
 
 		CompilerGenerated,
+		CompilerFeatureRequired,
 		/// <summary>
 		/// Marks a method as extension method; or a class as containing extension methods.
 		/// </summary>
@@ -119,6 +120,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		static readonly TopLevelTypeName[] typeNames = new TopLevelTypeName[Count]{
 			default,
 			new TopLevelTypeName("System.Runtime.CompilerServices", nameof(CompilerGeneratedAttribute)),
+			new TopLevelTypeName("System.Runtime.CompilerServices", "CompilerFeatureRequiredAttribute"),
 			new TopLevelTypeName("System.Runtime.CompilerServices", nameof(ExtensionAttribute)),
 			new TopLevelTypeName("System.Runtime.CompilerServices", nameof(DynamicAttribute)),
 			new TopLevelTypeName("System.Runtime.CompilerServices", nameof(TupleElementNamesAttribute)),