Avoid Attribute.GetCustomAttributes() returning null for open generic…

… type

* Revert "Revert "Avoid Attribute.GetCustomAttributes() returning null for open generic type (#65237)" (#66508)"

This reverts commit f99ba2e.

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

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

src/coreclr/System.Private.CoreLib/src/System/Attribute.CoreCLR.cs

@@ -434,10 +434,8 @@ private static AttributeUsageAttribute InternalGetAttributeUsage(Type type)
  SR.Format(SR.Format_AttributeUsage, type));
  }
 
- private static Attribute[] CreateAttributeArrayHelper(Type elementType, int elementCount)
- {
- return (Attribute[])Array.CreateInstance(elementType, elementCount);
- }
+ private static Attribute[] CreateAttributeArrayHelper(Type elementType, int elementCount) =>
+ elementType.ContainsGenericParameters ? new Attribute[elementCount] : (Attribute[])Array.CreateInstance(elementType, elementCount);
  #endregion
 
  #endregion
@@ -459,7 +457,7 @@ public static Attribute[] GetCustomAttributes(MemberInfo element!!, Type attribu
  {
  MemberTypes.Property => InternalGetCustomAttributes((PropertyInfo)element, attributeType, inherit),
  MemberTypes.Event => InternalGetCustomAttributes((EventInfo)element, attributeType, inherit),
- _ => (element.GetCustomAttributes(attributeType, inherit) as Attribute[])!,
+ _ => (Attribute[])element.GetCustomAttributes(attributeType, inherit)
  };
  }
 
@@ -474,7 +472,7 @@ public static Attribute[] GetCustomAttributes(MemberInfo element!!, bool inherit
  {
  MemberTypes.Property => InternalGetCustomAttributes((PropertyInfo)element, typeof(Attribute), inherit),
  MemberTypes.Event => InternalGetCustomAttributes((EventInfo)element, typeof(Attribute), inherit),
- _ => (element.GetCustomAttributes(typeof(Attribute), inherit) as Attribute[])!,
+ _ => (Attribute[])element.GetCustomAttributes(typeof(Attribute), inherit)
  };
  }
 
@@ -536,25 +534,23 @@ public static Attribute[] GetCustomAttributes(ParameterInfo element!!, Type attr
  if (element.Member == null)
  throw new ArgumentException(SR.Argument_InvalidParameterInfo, nameof(element));
 
-
  MemberInfo member = element.Member;
  if (member.MemberType == MemberTypes.Method && inherit)
  return InternalParamGetCustomAttributes(element, attributeType, inherit);
 
- return (element.GetCustomAttributes(attributeType, inherit) as Attribute[])!;
+ return (Attribute[])element.GetCustomAttributes(attributeType, inherit);
  }
 
  public static Attribute[] GetCustomAttributes(ParameterInfo element!!, bool inherit)
  {
  if (element.Member == null)
  throw new ArgumentException(SR.Argument_InvalidParameterInfo, nameof(element));
 
-
  MemberInfo member = element.Member;
  if (member.MemberType == MemberTypes.Method && inherit)
  return InternalParamGetCustomAttributes(element, null, inherit);
 
- return (element.GetCustomAttributes(typeof(Attribute), inherit) as Attribute[])!;
+ return (Attribute[])element.GetCustomAttributes(typeof(Attribute), inherit);
  }
 
  public static bool IsDefined(ParameterInfo element, Type attributeType)

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/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeCustomAttributeData.cs

@@ -899,7 +899,7 @@ internal static object[] GetCustomAttributes(RuntimeType type, RuntimeType caTyp
  Debug.Assert(caType is not null);
 
  if (type.GetElementType() is not null)
- return (caType.IsValueType) ? Array.Empty<object>() : CreateAttributeArrayHelper(caType, 0);
+ return CreateAttributeArrayHelper(caType, 0);
 
  if (type.IsGenericType && !type.IsGenericTypeDefinition)
  type = (type.GetGenericTypeDefinition() as RuntimeType)!;
@@ -919,8 +919,6 @@ internal static object[] GetCustomAttributes(RuntimeType type, RuntimeType caTyp
 
  RuntimeType.ListBuilder<object> result = default;
  bool mustBeInheritable = false;
- bool useObjectArray = (caType.IsValueType || caType.ContainsGenericParameters);
- RuntimeType arrayType = useObjectArray ? (RuntimeType)typeof(object) : caType;
 
  for (int i = 0; i < pcas.Count; i++)
  result.Add(pcas[i]);
@@ -932,7 +930,7 @@ internal static object[] GetCustomAttributes(RuntimeType type, RuntimeType caTyp
  type = (type.BaseType as RuntimeType)!;
  }
 
- object[] typedResult = CreateAttributeArrayHelper(arrayType, result.Count);
+ object[] typedResult = CreateAttributeArrayHelper(caType, result.Count);
  for (int i = 0; i < result.Count; i++)
  {
  typedResult[i] = result[i];
@@ -963,8 +961,6 @@ internal static object[] GetCustomAttributes(RuntimeMethodInfo method, RuntimeTy
 
  RuntimeType.ListBuilder<object> result = default;
  bool mustBeInheritable = false;
- bool useObjectArray = (caType.IsValueType || caType.ContainsGenericParameters);
- RuntimeType arrayType = useObjectArray ? (RuntimeType)typeof(object) : caType;
 
  for (int i = 0; i < pcas.Count; i++)
  result.Add(pcas[i]);
@@ -976,7 +972,7 @@ internal static object[] GetCustomAttributes(RuntimeMethodInfo method, RuntimeTy
  method = method.GetParentDefinition()!;
  }
 
- object[] typedResult = CreateAttributeArrayHelper(arrayType, result.Count);
+ object[] typedResult = CreateAttributeArrayHelper(caType, result.Count);
  for (int i = 0; i < result.Count; i++)
  {
  typedResult[i] = result[i];
@@ -1123,16 +1119,13 @@ private static bool IsCustomAttributeDefined(
  }
 
  private static object[] GetCustomAttributes(
- RuntimeModule decoratedModule, int decoratedMetadataToken, int pcaCount, RuntimeType? attributeFilterType)
+ RuntimeModule decoratedModule, int decoratedMetadataToken, int pcaCount, RuntimeType attributeFilterType)
  {
  RuntimeType.ListBuilder<object> attributes = default;
 
  AddCustomAttributes(ref attributes, decoratedModule, decoratedMetadataToken, attributeFilterType, false, default);
 
- bool useObjectArray = attributeFilterType is null || attributeFilterType.IsValueType || attributeFilterType.ContainsGenericParameters;
- RuntimeType arrayType = useObjectArray ? (RuntimeType)typeof(object) : attributeFilterType!;
-
- object[] result = CreateAttributeArrayHelper(arrayType, attributes.Count + pcaCount);
+ object[] result = CreateAttributeArrayHelper(attributeFilterType, attributes.Count + pcaCount);
  for (int i = 0; i < attributes.Count; i++)
  {
  result[i] = attributes[i];
@@ -1439,6 +1432,42 @@ internal static AttributeUsageAttribute GetAttributeUsage(RuntimeType decoratedA
 
  return attributeUsageAttribute ?? AttributeUsageAttribute.Default;
  }
+
+ internal static object[] CreateAttributeArrayHelper(RuntimeType caType, int elementCount)
+ {
+ bool useAttributeArray = false;
+ bool useObjectArray = false;
+
+ if (caType == typeof(Attribute))
+ {
+ useAttributeArray = true;
+ }
+ else if (caType.IsValueType)
+ {
+ useObjectArray = true;
+ }
+ else if (caType.ContainsGenericParameters)
+ {
+ if (caType.IsSubclassOf(typeof(Attribute)))
+ {
+ useAttributeArray = true;
+ }
+ else
+ {
+ useObjectArray = true;
+ }
+ }
+
+ if (useAttributeArray)
+ {
+ return elementCount == 0 ? Array.Empty<Attribute>() : new Attribute[elementCount];
+ }
+ if (useObjectArray)
+ {
+ return elementCount == 0 ? Array.Empty<object>() : new object[elementCount];
+ }
+ return elementCount == 0 ? caType.GetEmptyArray() : (object[])Array.CreateInstance(caType, elementCount);
+ }
  #endregion
 
  #region Private Static FCalls
@@ -1476,17 +1505,6 @@ private static void GetPropertyOrFieldData(
  module, &pBlobStart, (byte*)blobEnd, out name, out isProperty, out type, out value);
  blobStart = (IntPtr)pBlobStart;
  }
-
- private static object[] CreateAttributeArrayHelper(RuntimeType elementType, int elementCount)
- {
- // If we have 0 elements, don't allocate a new array
- if (elementCount == 0)
- {
- return elementType.GetEmptyArray();
- }
-
- return (object[])Array.CreateInstance(elementType, elementCount);
- }
  #endregion
  }
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeParameterInfo.cs

@@ -509,12 +509,12 @@ public override object[] GetCustomAttributes(bool inherit)
 
  public override object[] GetCustomAttributes(Type attributeType!!, bool inherit)
  {
- if (MdToken.IsNullToken(m_tkParamDef))
- return Array.Empty<object>();
-
  if (attributeType.UnderlyingSystemType is not RuntimeType attributeRuntimeType)
  throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
 
+ if (MdToken.IsNullToken(m_tkParamDef))
+ return CustomAttribute.CreateAttributeArrayHelper(attributeRuntimeType, 0);
+
  return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType);
  }
 

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Attribute.CoreRT.cs

@@ -141,19 +141,9 @@ private static Attribute[] Instantiate(IEnumerable<CustomAttributeData> cads, Ty
  attributes.Add(instantiatedAttribute);
  }
  int count = attributes.Count;
- Attribute[] result;
- try
- {
- result = (Attribute[])Array.CreateInstance(actualElementType, count);
- }
- catch (NotSupportedException) when (actualElementType.ContainsGenericParameters)
- {
- // This is here for desktop compatibility (using try-catch as control flow to avoid slowing down the mainline case.)
- // GetCustomAttributes() normally returns an array of the exact attribute type requested except when
- // the requested type is an open type. Its ICustomAttributeProvider counterpart would return an Object[] array but that's
- // not possible with this api's return type so it returns null instead.
- return null;
- }
+ Attribute[] result = actualElementType.ContainsGenericParameters
+ ? new Attribute[count]
+ : (Attribute[])Array.CreateInstance(actualElementType, count);
  attributes.CopyTo(result, 0);
  return result;
  }

src/libraries/System.Reflection/tests/ParameterInfoTests.cs

@@ -245,6 +245,14 @@ public void CustomAttributesInheritanceTest(int paramIndex, bool exists, int exp
  Assert.Equal(expectedMyAttributeValue, exists ? myAttribute.Value : expectedMyAttributeValue);
  }
 
+ [Fact]
+ public static void GetCustomAttributesOnParameterWithNullMetadataTokenReturnsArrayOfCorrectType()
+ {
+ var parameterWithNullMetadataToken = typeof(int[]).GetProperty(nameof(Array.Length)).GetMethod.ReturnParameter;
+ Assert.Equal(typeof(Attribute[]), Attribute.GetCustomAttributes(parameterWithNullMetadataToken).GetType());
+ Assert.Equal(typeof(MyAttribute[]), Attribute.GetCustomAttributes(parameterWithNullMetadataToken, typeof(MyAttribute)).GetType());
+ }
+
  [Fact]
  public void VerifyGetCustomAttributesData()
  {