Respecting EnumMemberAttribute in AOT'd applications

[eerhardt]

I'd like to NativeAOT compile a library that respects the EnumMemberAttribute. This attribute can be applied to enum fields to rename what the field name is used when serializing values of an enum.

The issue is, I can't statically know all the enum types that will be passed into my code. So I need to write code like this:

https://github.com/microsoft/kiota-abstractions-dotnet/blob/02afdff08829667ad7411e87b9dfa797809243a0/src/RequestInformation.cs#L187-L210

        private static object ReplaceEnumValueByStringRepresentation(object source)
        {
            if(source is Enum enumValue && GetEnumName(enumValue) is string enumValueName)
            {
                return enumValueName;
            }
            
            return source;
        }
        private static string? GetEnumName<T>(T value) where T : Enum
        {
            var type = value.GetType();

            if(Enum.GetName(type, value) is not { } name)
                throw new ArgumentException($"Invalid Enum value {value} for enum of type {type}");

            if(type.GetField(name)?.GetCustomAttribute<EnumMemberAttribute>() is { } attribute)
                return attribute.Value;

            return name.ToFirstCharacterLowerCase();

But I am getting a warning on value.GetType() and using it to call type.GetField(name).

In talking with @MichalStrehovsky and @agocke, one recommendation is that since enum fields cannot be trimmed, we can suppress this warning.

We should document this so people can justify suppressing this warning.

Additionally, it would be great if the analysis tooling understood that since T : Enum, and we are calling GetField on a System.Type that is guaranteed to be an enum, we shouldn't warn.

Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas
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Issue Details

---

I'd like to NativeAOT compile a library that respects the EnumMemberAttribute. This attribute can be applied to enum fields to rename what the field name is used when serializing values of an enum.

The issue is, I can't statically know all the enum types that will be passed into my code. So I need to write code like this:

https://github.com/microsoft/kiota-abstractions-dotnet/blob/02afdff08829667ad7411e87b9dfa797809243a0/src/RequestInformation.cs#L187-L210

        private static object ReplaceEnumValueByStringRepresentation(object source)
        {
            if(source is Enum enumValue && GetEnumName(enumValue) is string enumValueName)
            {
                return enumValueName;
            }
            
            return source;
        }
        private static string? GetEnumName<T>(T value) where T : Enum
        {
            var type = value.GetType();

            if(Enum.GetName(type, value) is not { } name)
                throw new ArgumentException($"Invalid Enum value {value} for enum of type {type}");

            if(type.GetField(name)?.GetCustomAttribute<EnumMemberAttribute>() is { } attribute)
                return attribute.Value;

            return name.ToFirstCharacterLowerCase();

But I am getting a warning on value.GetType() and using it to call type.GetField(name).

In talking with @MichalStrehovsky and @agocke, one recommendation is that since enum fields cannot be trimmed, we can suppress this warning.

We should document this so people can justify suppressing this warning.

Additionally, it would be great if the analysis tooling understood that since T : Enum, and we are calling GetField on a System.Type that is guaranteed to be an enum, we shouldn't warn.

Author:	eerhardt
Assignees:	-
Labels:	untriaged, area-NativeAOT-coreclr
Milestone:	-

[teo-tsirpanis]

I think that instead of type.GetValue() it should be using typeof(T). There is also a generic overload of Enum.GetName in modern frameworks.

[eerhardt]

I think that instead of type.GetValue() it should be using typeof(T). There is also a generic overload of Enum.GetName in modern frameworks.

Initially I agreed, until I saw the code in the top method:

        private static object ReplaceEnumValueByStringRepresentation(object source)
        {
            if(source is Enum enumValue && GetEnumName(enumValue) is string enumValueName)

here is a call to GetEnumName<System.Enum>(enumValue). So when this call happens, typeof(T) == typeof(System.Enum), which doesn't have the field, nor will it work with Enum.GetName.

The issue is, I can't statically know all the enum types that will be passed into my code.