[mono][reflection] ArgumentNullException calling `GetCustomAttributes` on user-defined subtype of `ParameterInfo`

[lambdageek]

The following code works with .NET 8.0 CoreCLR, but throws with Mono:

Program.cs:

using System.Reflection;

public class P {
 public static void Main()
 {
 var propi =typeof(P).GetProperty("Foo");
 var pi = new Retrofit.PropertyAsParameterInfo(propi!);
 IEnumerable<Attribute> cattrs = pi.GetCustomAttributes();
 Console.WriteLine($"Got {cattrs.Count()} attributes");
 foreach (var cattr in cattrs) {
 Console.WriteLine (cattr);
 }
 }

 [Flarg]
 [Blarg]
 public int Foo {get; set;}

 // public static void Foo([Flarg][Blarg]int i) {}
}

[AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property)]
public class FlargAttribute : Attribute {}

[AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property)]
public class BlargAttribute : Attribute {}

PropertyAsParameterInfo.cs:

using System.Reflection;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;

namespace Retrofit;

internal sealed class PropertyAsParameterInfo : ParameterInfo
{
 private readonly PropertyInfo _underlyingProperty;
 private readonly ParameterInfo? _constructionParameterInfo;

 public PropertyAsParameterInfo(PropertyInfo propertyInfo)
 {
 Debug.Assert(propertyInfo != null, "PropertyInfo must be provided.");

 AttrsImpl = (ParameterAttributes)propertyInfo.Attributes;
 NameImpl = propertyInfo.Name;
 MemberImpl = propertyInfo;
 ClassImpl = propertyInfo.PropertyType;

 // It is not a real parameter in the delegate, so,
 // not defining a real position.
 PositionImpl = -1;

 _underlyingProperty = propertyInfo;
 }
 public override bool HasDefaultValue
 => _constructionParameterInfo is not null && _constructionParameterInfo.HasDefaultValue;
 public override object? DefaultValue
 => _constructionParameterInfo?.DefaultValue;
 public override int MetadataToken => _underlyingProperty.MetadataToken;
 public override object? RawDefaultValue
 => _constructionParameterInfo?.RawDefaultValue;

 public override object[] GetCustomAttributes(Type attributeType, bool inherit)
 {
 var constructorAttributes = _constructionParameterInfo?.GetCustomAttributes(attributeType, inherit);

 if (constructorAttributes == null || constructorAttributes is { Length: 0 })
 {
 return _underlyingProperty.GetCustomAttributes(attributeType, inherit);
 }

 var propertyAttributes = _underlyingProperty.GetCustomAttributes(attributeType, inherit);

 var mergedAttributes = new Attribute[constructorAttributes.Length + propertyAttributes.Length];
 Array.Copy(constructorAttributes, mergedAttributes, constructorAttributes.Length);
 Array.Copy(propertyAttributes, 0, mergedAttributes, constructorAttributes.Length, propertyAttributes.Length);

 return mergedAttributes;
 }

 public override object[] GetCustomAttributes(bool inherit)
 {
 var constructorAttributes = _constructionParameterInfo?.GetCustomAttributes(inherit);

 if (constructorAttributes == null || constructorAttributes is { Length: 0 })
 {
 return _underlyingProperty.GetCustomAttributes(inherit);
 }

 var propertyAttributes = _underlyingProperty.GetCustomAttributes(inherit);

 // Since the constructors attributes should take priority we will add them first,
 // as we usually call it as First() or FirstOrDefault() in the argument creation
 var mergedAttributes = new object[constructorAttributes.Length + propertyAttributes.Length];
 Array.Copy(constructorAttributes, mergedAttributes, constructorAttributes.Length);
 Array.Copy(propertyAttributes, 0, mergedAttributes, constructorAttributes.Length, propertyAttributes.Length);

 return mergedAttributes;
 }

 public override IList<CustomAttributeData> GetCustomAttributesData()
 {
 var attributes = new List<CustomAttributeData>(
 _constructionParameterInfo?.GetCustomAttributesData() ?? Array.Empty<CustomAttributeData>());
 attributes.AddRange(_underlyingProperty.GetCustomAttributesData());

 return attributes.AsReadOnly();
 }

 public override Type[] GetOptionalCustomModifiers()
 => _underlyingProperty.GetOptionalCustomModifiers();

 public override Type[] GetRequiredCustomModifiers()
 => _underlyingProperty.GetRequiredCustomModifiers();

 public override bool IsDefined(Type attributeType, bool inherit)
 {
 return (_constructionParameterInfo is not null && _constructionParameterInfo.IsDefined(attributeType, inherit)) ||
 _underlyingProperty.IsDefined(attributeType, inherit);
 }
}

repro.csproj:

<Project Sdk="Microsoft.NET.Sdk">

 <PropertyGroup>
 <OutputType>Exe</OutputType>
 <TargetFramework>net8.0</TargetFramework>
 <ImplicitUsings>enable</ImplicitUsings>
 <Nullable>enable</Nullable>
 </PropertyGroup>
 <PropertyGroup Condition="false">
 <UseMonoRuntime>true</UseMonoRuntime>
 <SelfContained>true</SelfContained>
 </PropertyGroup>
</Project>

Expected output:

$ dotnet run
Got 2 attributes
FlargAttribute
BlargAttribute

Actual output

$ dotnet run
Unhandled Exception:
System.ArgumentNullException: Value cannot be null. (Parameter 'attributeType')
 at System.Reflection.CustomAttribute.GetCustomAttributes(ICustomAttributeProvider obj, Type attributeType, Boolean inherit)
 at System.Reflection.RuntimePropertyInfo.GetCustomAttributes(Type attributeType, Boolean inherit)
 at Retrofit.PropertyAsParameterInfo.GetCustomAttributes(Type attributeType, Boolean inherit) in /private/tmp/parma/PropertyAsParameterInfo.cs:line 42
 at System.Reflection.CustomAttribute.GetCustomAttributesBase(ICustomAttributeProvider obj, Type attributeType, Boolean inheritedOnly)
 at System.Reflection.CustomAttribute.GetCustomAttributes(ICustomAttributeProvider obj, Type attributeType, Boolean inherit)
 at System.Reflection.CustomAttribute.GetCustomAttributes(ICustomAttributeProvider obj, Boolean inherit)
 at System.Attribute.GetCustomAttributes(ParameterInfo element)
 at System.Reflection.CustomAttributeExtensions.GetCustomAttributes(ParameterInfo element)
 at P.Main() in /private/tmp/parma/Program.cs:line 9
[ERROR] FATAL UNHANDLED EXCEPTION: System.ArgumentNullException: Value cannot be null. (Parameter 'attributeType')
 at System.Reflection.CustomAttribute.GetCustomAttributes(ICustomAttributeProvider obj, Type attributeType, Boolean inherit)
 at System.Reflection.RuntimePropertyInfo.GetCustomAttributes(Type attributeType, Boolean inherit)
 at Retrofit.PropertyAsParameterInfo.GetCustomAttributes(Type attributeType, Boolean inherit) in /private/tmp/parma/PropertyAsParameterInfo.cs:line 42
 at System.Reflection.CustomAttribute.GetCustomAttributesBase(ICustomAttributeProvider obj, Type attributeType, Boolean inheritedOnly)
 at System.Reflection.CustomAttribute.GetCustomAttributes(ICustomAttributeProvider obj, Type attributeType, Boolean inherit)
 at System.Reflection.CustomAttribute.GetCustomAttributes(ICustomAttributeProvider obj, Boolean inherit)
 at System.Attribute.GetCustomAttributes(ParameterInfo element)
 at System.Reflection.CustomAttributeExtensions.GetCustomAttributes(ParameterInfo element)
 at P.Main() in /private/tmp/parma/Program.cs:line 9

[lambdageek]

Related to #94437 (comment). this is making aspnetcore tests fail when Mono is used as the runtime.

Also see #94437 (comment)

And in particular:

runtime/src/mono/System.Private.CoreLib/src/System/Reflection/CustomAttribute.cs

Lines 159 to 165 in 952ac21

	// FIXME: GetCustomAttributesBase doesn't like being passed a null attributeType
	if (attributeType == typeof(CustomAttribute))
	attributeType = null!;
	if (attributeType == typeof(Attribute))
	attributeType = null!;
	if (attributeType == typeof(object))
	attributeType = null!;

[lambdageek]

I think probably we shouldn't set attributeType = null as some kind of sentinel value that means "do a lookup without filtering the results". Just use a boolean

[lambdageek]

/cc @SamMonoRT

[tmds]

cc @uweigand @janani66 @Sapana-Khemkar @Swapnali911 @omajid

[janani66]

Can this be ported back to .NET 8 and .NET 7?

[ivanpovazan]

Reopening until all the backports are merged in:

• [release/6.0-staging] [mono] Fix GetCustomAttributes System.Reflection API with a custom attribute provider #94706
• [release/7.0-staging] [mono] Fix GetCustomAttributes System.Reflection API with a custom attribute provider #94708
• [release/8.0-staging] [mono] Fix GetCustomAttributes System.Reflection API with a custom attribute provider #94707