Work on #1204: Add optimized implementation of HasAttribute and GetAttribute to IEntity.

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -1491,7 +1491,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		EnumValueDisplayMode DetectBestEnumValueDisplayMode(ITypeDefinition typeDef, PEFile module)
 		{
-			if (typeDef.HasAttribute(KnownAttribute.Flags, inherit: false))
+			if (typeDef.HasAttribute(KnownAttribute.Flags))
 				return EnumValueDisplayMode.AllHex;
 			bool first = true;
 			long firstValue = 0, previousValue = 0;
@@ -1917,7 +1917,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			type = null;
 			elementCount = 0;
-			IAttribute attr = field.GetAttribute(KnownAttribute.FixedBuffer, inherit: false);
+			IAttribute attr = field.GetAttribute(KnownAttribute.FixedBuffer);
 			if (attr != null && attr.FixedArguments.Length == 2)
 			{
 				if (attr.FixedArguments[0].Value is IType trr && attr.FixedArguments[1].Value is int length)

ICSharpCode.Decompiler/CSharp/Resolver/CSharpOperators.cs

@@ -156,10 +156,9 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				get { return SymbolKind.Operator; }
 			}
 
-			IEnumerable<IAttribute> IEntity.GetAttributes()
-			{
-				return EmptyList<IAttribute>.Instance;
-			}
+			IEnumerable<IAttribute> IEntity.GetAttributes() => EmptyList<IAttribute>.Instance;
+			bool IEntity.HasAttribute(KnownAttribute attribute) => false;
+			IAttribute? IEntity.GetAttribute(KnownAttribute attribute) => null;
 
 			Accessibility IEntity.Accessibility {
 				get { return Accessibility.Public; }

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -1196,7 +1196,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		bool IsFlagsEnum(ITypeDefinition type)
 		{
-			return type.HasAttribute(KnownAttribute.Flags, inherit: false);
+			return type.HasAttribute(KnownAttribute.Flags);
 		}
 
 		Expression ConvertEnumValue(IType type, long val)

ICSharpCode.Decompiler/TypeSystem/ComHelper.cs

@@ -34,7 +34,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		{
 			return typeDefinition != null
 				&& typeDefinition.Kind == TypeKind.Interface
-				&& typeDefinition.HasAttribute(KnownAttribute.ComImport, inherit: false);
+				&& typeDefinition.HasAttribute(KnownAttribute.ComImport);
 		}
 
 		/// <summary>
@@ -46,7 +46,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		{
 			if (typeDefinition == null)
 				return SpecialType.UnknownType;
-			var coClassAttribute = typeDefinition.GetAttribute(KnownAttribute.CoClass, inherit: false);
+			var coClassAttribute = typeDefinition.GetAttribute(KnownAttribute.CoClass);
 			if (coClassAttribute != null && coClassAttribute.FixedArguments.Length == 1)
 			{
 				if (coClassAttribute.FixedArguments[0].Value is IType ty)

ICSharpCode.Decompiler/TypeSystem/IEntity.cs

@@ -68,6 +68,10 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </summary>
 		IEnumerable<IAttribute> GetAttributes();
 
+		bool HasAttribute(KnownAttribute attribute);
+
+		IAttribute? GetAttribute(KnownAttribute attribute);
+
 		/// <summary>
 		/// Gets the accessibility of this entity.
 		/// </summary>

ICSharpCode.Decompiler/TypeSystem/Implementation/AttributeListBuilder.cs

@@ -190,7 +190,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			foreach (var handle in attributes)
 			{
 				var attribute = metadata.GetCustomAttribute(handle);
-				// Attribute types shouldn't be generic (and certainly not open), so we don't need a generic context.
+				// Attribute types shouldn't be open generic, so we don't need a generic context.
 				var ctor = module.ResolveMethod(attribute.Constructor, new GenericContext());
 				var type = ctor.DeclaringType;
 				if (IgnoreAttribute(type, target))
@@ -205,6 +205,11 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		{
 			if (attributeType.DeclaringType != null || attributeType.TypeParameterCount != 0)
 				return false;
+			return IgnoreAttribute(new TopLevelTypeName(attributeType.Namespace, attributeType.Name), target);
+		}
+
+		internal bool IgnoreAttribute(TopLevelTypeName attributeType, SymbolKind target)
+		{
 			switch (attributeType.Namespace)
 			{
 				case "System.Runtime.CompilerServices":
@@ -259,6 +264,39 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			}
 		}
 
+		internal bool HasAttribute(MetadataReader metadata, CustomAttributeHandleCollection customAttributes, KnownAttribute attribute, SymbolKind symbolKind)
+		{
+			Debug.Assert(attribute.IsCustomAttribute());
+			foreach (var h in customAttributes)
+			{
+				var attr = metadata.GetCustomAttribute(h);
+				if (attr.IsKnownAttribute(metadata, attribute))
+				{
+					return !IgnoreAttribute(attribute.GetTypeName(), symbolKind);
+				}
+			}
+
+			return false;
+		}
+
+		internal IAttribute GetAttribute(MetadataReader metadata, CustomAttributeHandleCollection customAttributes, KnownAttribute attribute, SymbolKind symbolKind)
+		{
+			Debug.Assert(attribute.IsCustomAttribute());
+			foreach (var h in customAttributes)
+			{
+				var attr = metadata.GetCustomAttribute(h);
+				if (attr.IsKnownAttribute(metadata, attribute)
+					&& !IgnoreAttribute(attribute.GetTypeName(), symbolKind))
+				{
+					// Attribute types shouldn't be open generic, so we don't need a generic context.
+					var ctor = module.ResolveMethod(attr.Constructor, new GenericContext());
+					return new CustomAttribute(module, ctor, h);
+				}
+			}
+
+			return null;
+		}
+
 		static bool IsMethodLike(SymbolKind kind)
 		{
 			return kind switch {

ICSharpCode.Decompiler/TypeSystem/Implementation/FakeMember.cs

@@ -61,6 +61,8 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		IModule IEntity.ParentModule => DeclaringType?.GetDefinition()?.ParentModule;
 
 		IEnumerable<IAttribute> IEntity.GetAttributes() => EmptyList<IAttribute>.Instance;
+		bool IEntity.HasAttribute(KnownAttribute attribute) => false;
+		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => null;
 
 		public Accessibility Accessibility { get; set; } = Accessibility.Public;
 

ICSharpCode.Decompiler/TypeSystem/Implementation/KnownAttributes.cs

@@ -107,7 +107,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		PreserveBaseOverrides,
 	}
 
-	static class KnownAttributes
+	public static class KnownAttributes
 	{
 		internal const int Count = (int)KnownAttribute.PreserveBaseOverrides + 1;
 
@@ -197,5 +197,30 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			}
 			return KnownAttribute.None;
 		}
+
+		public static bool IsCustomAttribute(this KnownAttribute knownAttribute)
+		{
+			switch (knownAttribute)
+			{
+				case KnownAttribute.Serializable:
+				case KnownAttribute.ComImport:
+				case KnownAttribute.StructLayout:
+				case KnownAttribute.DllImport:
+				case KnownAttribute.PreserveSig:
+				case KnownAttribute.MethodImpl:
+				case KnownAttribute.FieldOffset:
+				case KnownAttribute.NonSerialized:
+				case KnownAttribute.MarshalAs:
+				case KnownAttribute.PermissionSet:
+				case KnownAttribute.Optional:
+				case KnownAttribute.In:
+				case KnownAttribute.Out:
+				case KnownAttribute.IndexerName:
+				case KnownAttribute.SpecialName:
+					return false;
+				default:
+					return true;
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/TypeSystem/Implementation/LocalFunctionMethod.cs

@@ -145,6 +145,8 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		public IType DeclaringType => baseMethod.DeclaringType;
 		public IModule ParentModule => baseMethod.ParentModule;
 		IEnumerable<IAttribute> IEntity.GetAttributes() => baseMethod.GetAttributes();
+		bool IEntity.HasAttribute(KnownAttribute attribute) => baseMethod.HasAttribute(attribute);
+		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => baseMethod.GetAttribute(attribute);
 		IEnumerable<IAttribute> IMethod.GetReturnTypeAttributes() => baseMethod.GetReturnTypeAttributes();
 		bool IMethod.ReturnTypeIsRefReadOnly => baseMethod.ReturnTypeIsRefReadOnly;
 		bool IMethod.ThisIsRefReadOnly => baseMethod.ThisIsRefReadOnly;

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataEvent.cs

@@ -123,6 +123,30 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			b.Add(eventDef.GetCustomAttributes(), SymbolKind.Event);
 			return b.Build();
 		}
+
+		public bool HasAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().Any(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetEventDefinition(handle);
+			return b.HasAttribute(metadata, def.GetCustomAttributes(), attribute, SymbolKind.Event);
+		}
+
+		public IAttribute GetAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().FirstOrDefault(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetEventDefinition(handle);
+			return b.GetAttribute(metadata, def.GetCustomAttributes(), attribute, SymbolKind.Event);
+		}
 		#endregion
 
 		public Accessibility Accessibility => AnyAccessor?.Accessibility ?? Accessibility.None;

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataField.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using System.Reflection;
 using System.Reflection.Metadata;
 using System.Reflection.Metadata.Ecma335;
@@ -164,6 +165,30 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return b.Build();
 		}
 
+		public bool HasAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().Any(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetFieldDefinition(handle);
+			return b.HasAttribute(metadata, def.GetCustomAttributes(), attribute, SymbolKind.Field);
+		}
+
+		public IAttribute GetAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().FirstOrDefault(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetFieldDefinition(handle);
+			return b.GetAttribute(metadata, def.GetCustomAttributes(), attribute, SymbolKind.Field);
+		}
+
 		public string FullName => $"{DeclaringType?.FullName}.{Name}";
 		public string ReflectionName => $"{DeclaringType?.ReflectionName}.{Name}";
 		public string Namespace => DeclaringType?.Namespace ?? string.Empty;

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataMethod.cs

@@ -463,6 +463,30 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 			return b.Build();
 		}
+
+		public bool HasAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().Any(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetMethodDefinition(handle);
+			return b.HasAttribute(metadata, def.GetCustomAttributes(), attribute, symbolKind);
+		}
+
+		public IAttribute GetAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().FirstOrDefault(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetMethodDefinition(handle);
+			return b.GetAttribute(metadata, def.GetCustomAttributes(), attribute, symbolKind);
+		}
 		#endregion
 
 		#region Return type attributes

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataProperty.cs

@@ -33,7 +33,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		const Accessibility InvalidAccessibility = (Accessibility)0xff;
 
 		readonly MetadataModule module;
-		readonly PropertyDefinitionHandle propertyHandle;
+		readonly PropertyDefinitionHandle handle;
 		readonly IMethod getter;
 		readonly IMethod setter;
 		readonly string name;
@@ -49,7 +49,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			Debug.Assert(module != null);
 			Debug.Assert(!handle.IsNil);
 			this.module = module;
-			this.propertyHandle = handle;
+			this.handle = handle;
 
 			var metadata = module.metadata;
 			var prop = metadata.GetPropertyDefinition(handle);
@@ -83,10 +83,10 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		public override string ToString()
 		{
-			return $"{MetadataTokens.GetToken(propertyHandle):X8} {DeclaringType?.ReflectionName}.{Name}";
+			return $"{MetadataTokens.GetToken(handle):X8} {DeclaringType?.ReflectionName}.{Name}";
 		}
 
-		public EntityHandle MetadataToken => propertyHandle;
+		public EntityHandle MetadataToken => handle;
 		public string Name => name;
 
 		public bool CanGet => getter != null;
@@ -122,14 +122,14 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		public bool ReturnTypeIsRefReadOnly {
 			get {
-				var propertyDef = module.metadata.GetPropertyDefinition(propertyHandle);
+				var propertyDef = module.metadata.GetPropertyDefinition(handle);
 				return propertyDef.GetCustomAttributes().HasKnownAttribute(module.metadata, KnownAttribute.IsReadOnly);
 			}
 		}
 
 		private void DecodeSignature()
 		{
-			var propertyDef = module.metadata.GetPropertyDefinition(propertyHandle);
+			var propertyDef = module.metadata.GetPropertyDefinition(handle);
 			var genericContext = new GenericContext(DeclaringType.TypeParameters);
 			IType returnType;
 			IParameter[] parameters;
@@ -201,7 +201,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		{
 			var b = new AttributeListBuilder(module);
 			var metadata = module.metadata;
-			var propertyDef = metadata.GetPropertyDefinition(propertyHandle);
+			var propertyDef = metadata.GetPropertyDefinition(handle);
 			if (IsIndexer && Name != "Item" && !IsExplicitInterfaceImplementation)
 			{
 				b.Add(KnownAttribute.IndexerName, KnownTypeCode.String, Name);
@@ -216,6 +216,30 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			b.Add(propertyDef.GetCustomAttributes(), symbolKind);
 			return b.Build();
 		}
+
+		public bool HasAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().Any(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetPropertyDefinition(handle);
+			return b.HasAttribute(metadata, def.GetCustomAttributes(), attribute, symbolKind);
+		}
+
+		public IAttribute GetAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().FirstOrDefault(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetPropertyDefinition(handle);
+			return b.GetAttribute(metadata, def.GetCustomAttributes(), attribute, symbolKind);
+		}
 		#endregion
 
 		#region Accessibility
@@ -278,14 +302,14 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		{
 			if (obj is MetadataProperty p)
 			{
-				return propertyHandle == p.propertyHandle && module.PEFile == p.module.PEFile;
+				return handle == p.handle && module.PEFile == p.module.PEFile;
 			}
 			return false;
 		}
 
 		public override int GetHashCode()
 		{
-			return 0x32b6a76c ^ module.PEFile.GetHashCode() ^ propertyHandle.GetHashCode();
+			return 0x32b6a76c ^ module.PEFile.GetHashCode() ^ handle.GetHashCode();
 		}
 
 		bool IMember.Equals(IMember obj, TypeVisitor typeNormalization)

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataTypeDefinition.cs

@@ -432,6 +432,30 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			return b.Build();
 		}
 
+		public bool HasAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().Any(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetTypeDefinition(handle);
+			return b.HasAttribute(metadata, def.GetCustomAttributes(), attribute, SymbolKind.TypeDefinition);
+		}
+
+		public IAttribute GetAttribute(KnownAttribute attribute)
+		{
+			if (!attribute.IsCustomAttribute())
+			{
+				return GetAttributes().FirstOrDefault(attr => attr.AttributeType.IsKnownType(attribute));
+			}
+			var b = new AttributeListBuilder(module);
+			var metadata = module.metadata;
+			var def = metadata.GetTypeDefinition(handle);
+			return b.GetAttribute(metadata, def.GetCustomAttributes(), attribute, SymbolKind.TypeDefinition);
+		}
+
 		public string DefaultMemberName {
 			get {
 				string defaultMemberName = LazyInit.VolatileRead(ref this.defaultMemberName);

ICSharpCode.Decompiler/TypeSystem/Implementation/MinimalCorlib.cs

@@ -258,10 +258,9 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				return EmptyList<IMethod>.Instance;
 			}
 
-			IEnumerable<IAttribute> IEntity.GetAttributes()
-			{
-				return EmptyList<IAttribute>.Instance;
-			}
+			IEnumerable<IAttribute> IEntity.GetAttributes() => EmptyList<IAttribute>.Instance;
+			bool IEntity.HasAttribute(KnownAttribute attribute) => false;
+			IAttribute IEntity.GetAttribute(KnownAttribute attribute) => null;
 
 			IEnumerable<IMethod> IType.GetConstructors(Predicate<IMethod> filter, GetMemberOptions options)
 			{

ICSharpCode.Decompiler/TypeSystem/Implementation/SpecializedMember.cs

@@ -162,6 +162,9 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		}
 
 		IEnumerable<IAttribute> IEntity.GetAttributes() => baseMember.GetAttributes();
+		bool IEntity.HasAttribute(KnownAttribute attribute) => baseMember.HasAttribute(attribute);
+		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => baseMember.GetAttribute(attribute);
+
 
 		public IEnumerable<IMember> ExplicitlyImplementedInterfaceMembers {
 			get {

ICSharpCode.Decompiler/TypeSystem/Implementation/SyntheticRangeIndexer.cs

@@ -126,6 +126,8 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		}
 
 		IEnumerable<IAttribute> IEntity.GetAttributes() => underlyingMethod.GetAttributes();
+		bool IEntity.HasAttribute(KnownAttribute attribute) => underlyingMethod.HasAttribute(attribute);
+		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => underlyingMethod.GetAttribute(attribute);
 
 		IEnumerable<IAttribute> IMethod.GetReturnTypeAttributes() => underlyingMethod.GetReturnTypeAttributes();
 

ICSharpCode.Decompiler/TypeSystem/InheritanceHelper.cs

@@ -185,6 +185,20 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			}
 		}
 
+		internal static IAttribute GetAttribute(ITypeDefinition typeDef, KnownAttribute attributeType)
+		{
+			foreach (var baseType in typeDef.GetNonInterfaceBaseTypes().Reverse())
+			{
+				ITypeDefinition baseTypeDef = baseType.GetDefinition();
+				if (baseTypeDef == null)
+					continue;
+				var attr = baseTypeDef.GetAttribute(attributeType);
+				if (attr != null)
+					return attr;
+			}
+			return null;
+		}
+
 		internal static IEnumerable<IAttribute> GetAttributes(IMember member)
 		{
 			HashSet<IMember> visitedMembers = new HashSet<IMember>();
@@ -202,6 +216,24 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				}
 			} while (member.IsOverride && (member = InheritanceHelper.GetBaseMember(member)) != null);
 		}
+
+		internal static IAttribute GetAttribute(IMember member, KnownAttribute attributeType)
+		{
+			HashSet<IMember> visitedMembers = new HashSet<IMember>();
+			do
+			{
+				member = member.MemberDefinition; // it's sufficient to look at the definitions
+				if (!visitedMembers.Add(member))
+				{
+					// abort if we seem to be in an infinite loop (cyclic inheritance)
+					break;
+				}
+				var attr = member.GetAttribute(attributeType);
+				if (attr != null)
+					return attr;
+			} while (member.IsOverride && (member = InheritanceHelper.GetBaseMember(member)) != null);
+			return null;
+		}
 		#endregion
 	}
 }

ICSharpCode.Decompiler/TypeSystem/TypeSystemExtensions.cs

@@ -485,7 +485,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 
 		#region IEntity.GetAttribute
 		/// <summary>
-		/// Gets whether the entity has an attribute of the specified attribute type (or derived attribute types).
+		/// Gets whether the entity has an attribute of the specified attribute type.
 		/// </summary>
 		/// <param name="entity">The entity on which the attributes are declared.</param>
 		/// <param name="attributeType">The attribute type to look for.</param>
@@ -494,13 +494,16 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// (if the given <paramref name="entity"/> in an <c>override</c>)
 		/// should be returned.
 		/// </param>
-		public static bool HasAttribute(this IEntity entity, KnownAttribute attributeType, bool inherit = false)
+		public static bool HasAttribute(this IEntity entity, KnownAttribute attributeType, bool inherit)
 		{
+			if (!inherit)
+				return entity.HasAttribute(attributeType);
+
 			return GetAttribute(entity, attributeType, inherit) != null;
 		}
 
 		/// <summary>
-		/// Gets the attribute of the specified attribute type (or derived attribute types).
+		/// Gets the attribute of the specified attribute type.
 		/// </summary>
 		/// <param name="entity">The entity on which the attributes are declared.</param>
 		/// <param name="attributeType">The attribute type to look for.</param>
@@ -514,9 +517,27 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// If inherit is true, an from the entity itself will be returned if possible;
 		/// and the base entity will only be searched if none exists.
 		/// </returns>
-		public static IAttribute GetAttribute(this IEntity entity, KnownAttribute attributeType, bool inherit = false)
+		public static IAttribute GetAttribute(this IEntity entity, KnownAttribute attributeType, bool inherit)
 		{
-			return GetAttributes(entity, inherit).FirstOrDefault(a => a.AttributeType.IsKnownType(attributeType));
+			if (inherit)
+			{
+				if (entity is ITypeDefinition td)
+				{
+					return InheritanceHelper.GetAttribute(td, attributeType);
+				}
+				else if (entity is IMember m)
+				{
+					return InheritanceHelper.GetAttribute(m, attributeType);
+				}
+				else
+				{
+					throw new NotSupportedException("Unknown entity type");
+				}
+			}
+			else
+			{
+				return entity.GetAttribute(attributeType);
+			}
 		}
 
 		/// <summary>
@@ -559,7 +580,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 
 		#region IParameter.GetAttribute
 		/// <summary>
-		/// Gets whether the parameter has an attribute of the specified attribute type (or derived attribute types).
+		/// Gets whether the parameter has an attribute of the specified attribute type.
 		/// </summary>
 		/// <param name="parameter">The parameter on which the attributes are declared.</param>
 		/// <param name="attributeType">The attribute type to look for.</param>
@@ -569,7 +590,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		}
 
 		/// <summary>
-		/// Gets the attribute of the specified attribute type (or derived attribute types).
+		/// Gets the attribute of the specified attribute type.
 		/// </summary>
 		/// <param name="parameter">The parameter on which the attributes are declared.</param>
 		/// <param name="attributeType">The attribute type to look for.</param>

ICSharpCode.Decompiler/TypeSystem/VarArgInstanceMethod.cs

@@ -118,6 +118,9 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		}
 
 		IEnumerable<IAttribute> IEntity.GetAttributes() => baseMethod.GetAttributes();
+		bool IEntity.HasAttribute(KnownAttribute attribute) => baseMethod.HasAttribute(attribute);
+		IAttribute IEntity.GetAttribute(KnownAttribute attribute) => baseMethod.GetAttribute(attribute);
+
 		IEnumerable<IAttribute> IMethod.GetReturnTypeAttributes() => baseMethod.GetReturnTypeAttributes();
 		bool IMethod.ReturnTypeIsRefReadOnly => baseMethod.ReturnTypeIsRefReadOnly;
 		bool IMethod.ThisIsRefReadOnly => baseMethod.ThisIsRefReadOnly;

ILSpy/Analyzers/Builtin/AttributeAppliedToAnalyzer.cs

@@ -51,26 +51,7 @@ namespace ICSharpCode.ILSpy.Analyzers.Builtin
 		bool IsBuiltinAttribute(ITypeDefinition attributeType, out KnownAttribute knownAttribute)
 		{
 			knownAttribute = attributeType.IsBuiltinAttribute();
-			switch (knownAttribute)
-			{
-				case KnownAttribute.Serializable:
-				case KnownAttribute.ComImport:
-				case KnownAttribute.StructLayout:
-				case KnownAttribute.DllImport:
-				case KnownAttribute.PreserveSig:
-				case KnownAttribute.MethodImpl:
-				case KnownAttribute.FieldOffset:
-				case KnownAttribute.NonSerialized:
-				case KnownAttribute.MarshalAs:
-				case KnownAttribute.PermissionSet:
-				case KnownAttribute.Optional:
-				case KnownAttribute.In:
-				case KnownAttribute.Out:
-				case KnownAttribute.IndexerName:
-					return true;
-				default:
-					return false;
-			}
+			return !knownAttribute.IsCustomAttribute();
 		}
 
 		IEnumerable<IEnumerable<ISymbol>> HandleBuiltinAttribute(KnownAttribute attribute, AnalyzerScope scope, CancellationToken ct)