Zig breaking change – Initial Writergate

I maintain the zigler library, and one thing that was useful about the old async "colored-but-not-really" functions was that they implicitly tolerate having internal suspend points (detail: https://www.youtube.com/watch?v=lDfjdGva3NE&t=1819s) -- I'm not sure if having IO be a passed parameter will still let me do that? Can users build their own functions with yield points? And will you be able to jump out of the frame of a function and give control back to the executor, to let it resume later?

As you're aware, that feature of the language ("stackless coroutines", "generators", "rewriting function logic into a state machine") was regressed. At first, this new IO interface won't have that capability.

However, as a followup issue, I'd like to reintroduce it, potentially in more low-level manner, for use inside IO implementations. Combined with restricted function pointers, this will allow functions that can suspend to pass through runtime-known function pointer boundaries - something that was terribly clunky before to the point that it compromised the entire design. This means that, again, the same IO interface usage code will be able to be reused, including when the implementation uses suspend points, and the automatic calling convention rewriting will be able to propagate through the interface into the usage code.

The issue to track is: https://github.com/ziglang/zig/issues/23446

I'll add that I'm still keen on the previous suspend/resume keywords and semantics as a solution to this issue.