Make DynamicMethod.GetCustomAttributes() return well-typed arrays.

This change makes DynamicMethod.GetCustomAttributes() compatible with
Attribute.GetCustomAttributes().

Fix dotnet#66496

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/DynamicMethod.cs

@@ -624,15 +624,18 @@ public override object Invoke(object? obj, BindingFlags invokeAttr, Binder? bind
  throw new ArgumentException(SR.Argument_MustBeRuntimeMethodInfo, "this");
  }
 
- public override object[] GetCustomAttributes(Type attributeType, bool inherit)
+ public override object[] GetCustomAttributes(Type attributeType!!, bool inherit)
  {
- if (attributeType == null)
- throw new ArgumentNullException(nameof(attributeType));
+ if (attributeType.UnderlyingSystemType is not RuntimeType attributeRuntimeType)
+ throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
 
- if (attributeType.IsAssignableFrom(typeof(MethodImplAttribute)))
- return new object[] { new MethodImplAttribute((MethodImplOptions)GetMethodImplementationFlags()) };
- else
- return Array.Empty<object>();
+ bool includeMethodImplAttribute = attributeType.IsAssignableFrom(typeof(MethodImplAttribute));
+ object[] result = CustomAttribute.CreateAttributeArrayHelper(attributeRuntimeType, includeMethodImplAttribute ? 1 : 0);
+ if (includeMethodImplAttribute)
+ {
+ result[0] = new MethodImplAttribute((MethodImplOptions)GetMethodImplementationFlags());
+ }
+ return result;
  }
 
  public override object[] GetCustomAttributes(bool inherit)

src/libraries/System.Runtime/tests/System/Attributes.cs

@@ -17,6 +17,8 @@
 using System.Reflection;
 using System.Linq;
 using System.Diagnostics;
+using System.Reflection.Emit;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using Xunit;
 
@@ -220,54 +222,74 @@ public static void GetCustomAttributes_Interface()
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ public static void GetCustomAttributes_DynamicMethod()
+ {
+ var dynamicMethod = new DynamicMethod("test", typeof(void), Type.EmptyTypes);
+ dynamicMethod.GetILGenerator().Emit(OpCodes.Ret);
+ var action = (Action)dynamicMethod.CreateDelegate(typeof(Action));
+
+ Attribute[] attributes = Attribute.GetCustomAttributes(action.Method, typeof(NameableAttribute));
+ Assert.Empty(attributes);
+ Assert.IsType<NameableAttribute[]>(attributes);
+
+ attributes = Attribute.GetCustomAttributes(action.Method);
+ Assert.Equal(1, attributes.Length);
+ Assert.IsType<MethodImplAttribute>(attributes[0]);
+
+ attributes = Attribute.GetCustomAttributes(action.Method, typeof(MethodImplAttribute));
+ Assert.Equal(1, attributes.Length);
+ Assert.IsType<MethodImplAttribute[]>(attributes);
+ }
+
+ [Fact]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForType()
  {
  GenericAttributesTestHelper<string>(t => Attribute.GetCustomAttributes(typeof(HasGenericAttribute), t));
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForField()
  {
  FieldInfo field = typeof(HasGenericAttribute).GetField(nameof(HasGenericAttribute.Field), BindingFlags.NonPublic | BindingFlags.Instance);
  GenericAttributesTestHelper<TimeSpan>(t => Attribute.GetCustomAttributes(field, t));
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForConstructor()
  {
  ConstructorInfo method = typeof(HasGenericAttribute).GetConstructor(Type.EmptyTypes);
  GenericAttributesTestHelper<Guid>(t => Attribute.GetCustomAttributes(method, t));
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForMethod()
  {
  MethodInfo method = typeof(HasGenericAttribute).GetMethod(nameof(HasGenericAttribute.Method));
  GenericAttributesTestHelper<long>(t => Attribute.GetCustomAttributes(method, t));
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForParameter()
  {
  ParameterInfo parameter = typeof(HasGenericAttribute).GetMethod(nameof(HasGenericAttribute.Method)).GetParameters()[0];
  GenericAttributesTestHelper<ulong>(t => Attribute.GetCustomAttributes(parameter, t));
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForProperty()
  {
  PropertyInfo property = typeof(HasGenericAttribute).GetProperty(nameof(HasGenericAttribute.Property));
  GenericAttributesTestHelper<List<object>>(t => Attribute.GetCustomAttributes(property, t));
  }
 
  [Fact]
- [ActiveIssue("https://github.com/dotnet/runtime/issues/56887)", TestRuntimes.Mono)]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/56887", TestRuntimes.Mono)]
  public static void GetCustomAttributesWorksWithOpenAndClosedGenericTypesForEvent()
  {
  EventInfo @event = typeof(HasGenericAttribute).GetEvent(nameof(HasGenericAttribute.Event));

src/mono/System.Private.CoreLib/src/System/Reflection/Emit/DynamicMethod.cs

@@ -247,16 +247,17 @@ public override object[] GetCustomAttributes(bool inherit)
  return new object[] { new MethodImplAttribute((MethodImplOptions)GetMethodImplementationFlags()) };
  }
 
- public override object[] GetCustomAttributes(Type attributeType,
- bool inherit)
+ public override object[] GetCustomAttributes(Type attributeType!!, bool inherit)
  {
- if (attributeType == null)
- throw new ArgumentNullException(nameof(attributeType));
-
  if (attributeType.IsAssignableFrom(typeof(MethodImplAttribute)))
- return new object[] { new MethodImplAttribute((MethodImplOptions)GetMethodImplementationFlags()) };
- else
- return Array.Empty<object>();
+ {
+ // avoid calling CreateInstance() in the common case where the type is Attribute
+ object[] result = attributeType == typeof(Attribute) ? new Attribute[1] : (object[])Array.CreateInstance(attributeType, 1);
+ result[0] = new MethodImplAttribute((MethodImplOptions)GetMethodImplementationFlags());
+ return result;
+ }
+
+ return (object[])Array.CreateInstance(attributeType.IsValueType || attributeType.ContainsGenericParameters ? typeof(object) : attributeType, 0);
  }
 
  public DynamicILInfo GetDynamicILInfo()