Enum class struct props serialized differently to enum values

[qaisjp]

Input

→ View on sorbet.run

# typed: true
extend T::Sig

class Kind < T::Enum
  enums do
    X = new
    Y = new
  end
end

class Foo < T::Struct
  prop :type, Kind
end

class Bar < T::Struct
  prop :type, Kind::X, default: Kind::X
end

a = Foo.new(type: Kind::X).serialize # {"type"=>"x"}
b = Bar.new.serialize # {"type"=>#<Foo::X>}

# $ a == b
# true
#
# Which makes sense, because Kind::X == "x"

Observed output

a = Foo.new(type: Kind::X).serialize # {"type"=>"x"}
b = Bar.new.serialize # {"type"=>#<Foo::X>}

Expected behavior

Bar should be serialized identically to Foo. The only difference that Bar has to Foo, is that Bar only allows Kind::X to be passed, whereas Foo allows any value in Kind.

a = Foo.new(type: Kind::X).serialize # {"type"=>"x"}
b = Bar.new.serialize # {"type"=>"x"}

[jez]

It looks like we only do handle_custom_type for the T::Types::Simple case. Sorbet stores the Kind::X types as T::Types::TEnum types, which are not T::Types::Simple

https://github.com/sorbet/sorbet/blob/master/gems/sorbet-runtime/lib/types/props/private/serde_transform.rb#L64-L79

So we need to add a case for T::Types::TEnum, and call handle_custom_type in it.

Also worth noting: I'm not 100% sure that the above file is the only place that the serde code lives in sorbet-runtime right now—it might be duplicated in both the dynamically-generated serde methods as well as another, equivalent place that doesn't use eval, so we would want to double check that.