Fix #3094: look for `[NullableAttribute]` both on the property getter and property itself

ICSharpCode.Decompiler/TypeSystem/ApplyAttributeTypeVisitor.cs

@@ -40,7 +40,8 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			SRM.MetadataReader metadata,
 			TypeSystemOptions options,
 			Nullability nullableContext,
-			bool typeChildrenOnly = false)
+			bool typeChildrenOnly = false,
+			SRM.CustomAttributeHandleCollection? additionalAttributes = null)
 		{
 			bool hasDynamicAttribute = false;
 			bool[] dynamicAttributeData = null;
@@ -57,10 +58,8 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			{
 				nullability = Nullability.Oblivious;
 			}
-			const TypeSystemOptions relevantOptions = TypeSystemOptions.Dynamic | TypeSystemOptions.Tuple | TypeSystemOptions.NullabilityAnnotations | TypeSystemOptions.NativeIntegers;
-			if (attributes != null && (options & relevantOptions) != 0)
-			{
-				foreach (var attrHandle in attributes.Value)
+
+			void ProcessAttribute(SRM.CustomAttributeHandle attrHandle)
 			{
 				var attr = metadata.GetCustomAttribute(attrHandle);
 				var attrType = attr.GetAttributeType(metadata);
@@ -123,6 +122,22 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					}
 				}
 			}
+
+			const TypeSystemOptions relevantOptions = TypeSystemOptions.Dynamic | TypeSystemOptions.Tuple | TypeSystemOptions.NullabilityAnnotations | TypeSystemOptions.NativeIntegers;
+			if (attributes != null && (options & relevantOptions) != 0)
+			{
+				foreach (var attrHandle in attributes.Value)
+				{
+					ProcessAttribute(attrHandle);
+				}
+			}
+			if (additionalAttributes != null && (options & relevantOptions) != 0)
+			{
+				// Note: additional attributes will override the values from the normal attributes.
+				foreach (var attrHandle in additionalAttributes.Value)
+				{
+					ProcessAttribute(attrHandle);
+				}
 			}
 			if (hasDynamicAttribute || hasNativeIntegersAttribute || nullability != Nullability.Oblivious || nullableAttributeData != null
 				|| (options & (TypeSystemOptions.Tuple | TypeSystemOptions.KeepModifiers)) != TypeSystemOptions.KeepModifiers)

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataMethod.cs

@@ -209,13 +209,14 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			MetadataModule module, IParameterizedMember owner,
 			MethodSignature<IType> signature, ParameterHandleCollection? parameterHandles,
 			Nullability nullableContext, TypeSystemOptions typeSystemOptions,
-			CustomAttributeHandleCollection? returnTypeAttributes = null)
+			CustomAttributeHandleCollection? additionalReturnTypeAttributes = null)
 		{
 			var metadata = module.metadata;
 			int i = 0;
 			IParameter[] parameters = new IParameter[signature.RequiredParameterCount
 				+ (signature.Header.CallingConvention == SignatureCallingConvention.VarArgs ? 1 : 0)];
 			IType parameterType;
+			CustomAttributeHandleCollection? returnTypeAttributes = null;
 			if (parameterHandles != null)
 			{
 				foreach (var parameterHandle in parameterHandles)
@@ -225,14 +226,13 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 					{
 						// "parameter" holds return type attributes.
 						// Note: for properties, the attributes normally stored on a method's return type
-						// are instead stored as normal attributes on the property.
-						// So MetadataProperty provides a non-null value for returnTypeAttributes,
-						// which then should be preferred over the attributes on the accessor's parameters.
-						if (returnTypeAttributes == null)
-						{
+						// are instead typically stored as normal attributes on the property.
+						// So MetadataProperty provides a non-null value for additionalReturnTypeAttributes,
+						// which then will be preferred over the attributes on the accessor's parameters.
+						// However if an attribute only exists on the accessor's parameters, we still want
+						// to process it here.
 						returnTypeAttributes = par.GetCustomAttributes();
 					}
-					}
 					else if (i < par.SequenceNumber && par.SequenceNumber <= signature.RequiredParameterCount)
 					{
 						// "Successive rows of the Param table that are owned by the same method shall be

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataProperty.cs

@@ -169,7 +169,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				(returnType, parameters, _) = MetadataMethod.DecodeSignature(
 					module, this, signature,
 					parameterHandles, nullableContext, typeOptions,
-					returnTypeAttributes: propertyDef.GetCustomAttributes());
+					additionalReturnTypeAttributes: propertyDef.GetCustomAttributes());
 			}
 			catch (BadImageFormatException)
 			{