[API Proposal]: Add option to specify JsonNamingPolicy for enum serialization on JsonSourceGenerationOptions

[ithline]

Background and motivation

Recently there has been added UseStringEnumConverter flag to JsonSourceGenerationOptions, but there is no way to configure naming policy for these converters.

The Converters property accepts Type[]? array, so it cannot be used either.

API Proposal

namespace System.Text.Json.Serialization;

public partial class JsonSourceGenerationOptionsAttribute : JsonAttribute
{
    public JsonKnownNamingPolicy EnumNamingPolicy { get; set; }
}

API Usage

[JsonSourceGenerationOptions(
    UseStringEnumConverter = true,
    EnumNamingPolicy = JsonKnownNamingPolicy.CamelCase)]
internal sealed partial class MyJsonContext : JsonSerializerContext
{
}

Alternative Designs

No response

Risks

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis See info in area-owners.md if you want to be subscribed.

Issue Details

---

### Background and motivation Recently there has been added `UseStringEnumConverter` flag to `JsonSourceGenerationOptions`, but there is no way to configure naming policy for these converters. The `Converters` property accepts `Type[]?` array, so it cannot be used either. ### API Proposal ```csharp namespace System.Text.Json.Serialization; public partial class JsonSourceGenerationOptionsAttribute : JsonAttribute { public JsonKnownNamingPolicy EnumNamingPolicy { get; set; } } ``` ### API Usage ```csharp [JsonSourceGenerationOptions( UseStringEnumConverter = true, EnumNamingPolicy = JsonKnownNamingPolicy.CamelCase)] internal sealed partial class MyJsonContext : JsonSerializerContext { } ``` ### Alternative Designs _No response_ ### Risks _No response_

Author:	ithline
Assignees:	-
Labels:	`api-suggestion`, `area-System.Text.Json`
Milestone:	-

[eiriktsarpalis]

Sounds reasonable.

[eiriktsarpalis]

The Converters property accepts Type[]? array, so it cannot be used either.

You can always try extending the converter class with a custom naming policy and specify that in the Converters property:

public enum MyEnum { A, B, C };

[JsonSourceGenerationOptions(Converters = new[] { typeof(CamelCaseJsonStringEnumConverter<MyEnum>)})]
[JsonSerializable(typeof(MyEnum))]
public partial class MyContext : JsonSerializerContext { }

public class CamelCaseJsonStringEnumConverter<TEnum>() 
    : JsonStringEnumConverter<TEnum>(JsonNamingPolicy.CamelCase) where TEnum : struct, Enum;

[alexanderdibenedetto]

This would solve a lot of issues with the fact that the JsonStringEnumConverter locks you into CamelCase, and some of us need snake or kebob case instead for certain enumerations.

[Pentadome]

The Converters property accepts Type[]? array, so it cannot be used either.

You can always try extending the converter class with a custom naming policy and specify that in the Converters property:

public enum MyEnum { A, B, C };

[JsonSourceGenerationOptions(Converters = new[] { typeof(CamelCaseJsonStringEnumConverter<MyEnum>)})]
[JsonSerializable(typeof(MyEnum))]
public partial class MyContext : JsonSerializerContext { }

public class CamelCaseJsonStringEnumConverter<TEnum>() 
    : JsonStringEnumConverter<TEnum>(JsonNamingPolicy.CamelCase) where TEnum : struct, Enum;

Or you can make a factory to support all enums.

internal sealed class JsonStringEnumCamelCaseConverter : JsonConverterFactory
{
    public override bool CanConvert(Type typeToConvert)
    {
        return typeToConvert.IsEnum;
    }

    public override JsonConverter? CreateConverter(
        Type typeToConvert,
        JsonSerializerOptions options
    )
    {
        if (!typeToConvert.IsEnum)
            throw new ArgumentException("Type should be enum.", nameof(typeToConvert));

        var constructedType = typeof(JsonStringEnumConverter<>).MakeGenericType(typeToConvert);
        return (JsonConverter)
            Activator.CreateInstance(
                constructedType,
                BindingFlags.Default,
                null,
                [JsonNamingPolicy.CamelCase, true],
                null
            )!;
    }
}