Deprecate strawberry.union('name', types=(A, B)) in favour of using Annoted

[patrick91]

So, I though having our own way of defining union type was a good idea, but turns out it is quite hard to make a mypy plugin that understands this syntax:

Result = strawberry.union("Result", (A, B))

also this won't really be supported in other type checkers, so the alternative is this:

Result = Annotated[Union[A, B], strawberry.union("Result")]

which is not that bad, also this allows to define named unions on fields directly:

@strawberry.type
class X:
     result: Annotated[Union[A, B], strawberry.union("Result")]

which isn't the best thing to ready, but might be useful in some cases :D

[BryceBeagle]

turns out it is quite hard to make a mypy plugin that understands this syntax:

Result = strawberry.union("Result", (A, B))

what about this requires a mypy extension? Or does the usage of Result cause problems?

[patrick91]

@BryceBeagle so, we need the plugin to tell mypy that result now is a Type, more specifically a TypeAlias so that you can do things like A: Result.

Unfortunately our current plugin seems to break in some cases, and I'm having a hard time finding a solution, basically here:

https://github.com/strawberry-graphql/strawberry/blob/master/strawberry/ext/mypy_plugin.py#L55

one of the type breaks api.named_type(expr.name), but I have no idea why, from what I've seen it seems that mypy things the type is coming from a variable, but well, it comes from an import 🤷

[BryceBeagle]

Does PEP-613 not work for this case?

Result: TypeAlias = strawberry.union("Result", (A, B, C))

[patrick91]

@BryceBeagle didn't know about that one! I think the problem would still be that mypy doesn't know the actual type of Result :(

[patrick91]

Oh well, turns out we can't do this for now, as mypy doesn't support it, from python/mypy#9315

Because A = Annotated[int, Positive] works, and so does x: Annotated[int, Positive()], but indeed B = Annotated[int, Positive()] does not.

[patrick91]

We might not deprecate strawberry.union, but we might introduce support for the annotated version, when the next release of mypy gets released :)

[rmzr7]

@patrick91 has a new annotated version been released yet or is Result = strawberry.union("Result", (A, B)) still the preferred way of using union types?

[patrick91]

@patrick91 has a new annotated version been released yet or is Result = strawberry.union("Result", (A, B)) still the preferred way of using union types?

we are keeping strawberry.union 😊

[jkimbo]

Can we close this issue then @patrick91 ?

[patrick91]

let's close for now, maybe we'll come back to it in future 😊