Recent fix to orjson serialization breaks unions

[orinatic]

• cattrs version: 22.1.0.dev0
• Python version: 3.7
• Operating System: Ubuntu 16.04

Description

Orjson doesn't like it when classes have union types as entries. It doesn't always happen, but it does in the case I'm actually working on.

What I Did

Unfortunately, I've been unable to come up with a small example for this one, but I can explain the error:

in orjson.py, there is the section:

        if args:
            if (issubclass(args[0], str) and issubclass(args[0], Enum)):

                def key_handler(v):
                    return v.value

I have managed to get args[0] to be a typing.Union type, which means that this crashes, since issubclass only works on type objects, and typing.Union is not a type object.

This can be fixed by changing it to

        if args:
            if (isinstance(args[0], type) and
                issubclass(args[0], str) and
                issubclass(args[0], Enum)):

                def key_handler(v):
                    return v.value

I suspect this might be the case in other converters as well, but since I'm using orjson, that's the one I ran into it in

[Tinche]

Ugh, I've been bitten by the unsafe issubclass builtin in another project. I think the easiest solution is just to create our own is_subclass, which eats any exceptions and just returns false.