Adds support for targeting an async method's internal MoveNext method

[Banane9]

As the title says. This is particularly interesting for targeting an async method with a transpiler, whether using Attributes or manually finding it with the added AsyncMoveNext method in AccessTools.

I'm not sure where the tests should go / how they should look, but I did test it on a game that I write mods for.
Works perfectly, although trying to use IAsyncStateMachine as the type for the __instance parameter causes a FormatException for invalid IL on the call to the patch method (that took a while to figure out).

[pardeike]

What’s the difference to MethodType.Enumerator ?

[Banane9]

Well, with MethodType.Enumerator it fails to find the method to patch, as it looks for a newobj opcode - but the actual contents of async methods don't use that.

Looking at an iterator method, those are also decorated with an IteratorStateMachineAttribute, which contains a reference to the type. They both share the StateMachineAttribute as a parent, so I suppose it could be merged together into a StateMachine one too (though that wouldn't be backwards compatible, I guess).

[Banane9]

Anything that would have to be changed/added for this? 👀

A game I'm working with has quite a few async methods, so it would be nice to target them more easily.

[pardeike]

I would still like to see if we can merge this with the existing api. You mentioned that this would break backwards compatibility, in what way would that be a problem?

[Banane9]

I just mentioned it as a consideration - I don't know how you handle that sort of thing for Harmony.

Funnily enough, the way I understand it, renaming the MethodType.Enumerator enum value to something like MethodType.StateMachine and handling both through that would keep it binary compatible (as enum values are embedded directly as their numeric values), but code using it would have to be changed.

Though even that could be avoided by defining it as a second entry in the enum with the same underlying value and marking the old one as obsolete / removing it with a major version release - though I don't know if you care about keeping that sort of compatibility.

[pardeike]

Just that one tiny cleanup