[Pitch] Generalize `conformance` macros as `extension` macros

[taylorswift]

@beccadax

@jaredh159

apologies if this is a dumb question, but after looking over the pitch, i'm still not clear on one thing: will extension macros be able to declare conformances, and then implement them while still having access to the type members?

Yes. In the signature Holly mentioned:

okay, i know the proposal has been accepted already, but i’m running into a similar problem with extension macros, where i have a huge list of names i’m currently passing directly to the attached macro attribute, and i would really rather the list of names live elsewhere, preferably in an extension block in a different file.

as far as i can tell, the attachedTo:some DeclGroupSyntax argument only contains the main declaration block the attribute is attached to, and the attribute itself can only be attached to the main declaration block.

as far as i understand, there is nowhere this giant list of constant data can live, except inline at the top of the main declaration of the type it’s attached to, which is pretty much the worst possible place it could be.