Still reproducible with Xcode 13.1 (downloaded as 13.1 RC)

I would add that this kind of issue is particularly time-consuming to encounter, given Swift's propensity for long compile times: at first I have to assume this is one of these cases, and therefore attempt to reduce inference complexity among other sources of long compiles, before I am allowed to conclude this is an infinite loop in the compiler. In fact, every time I have to reproduce it I have to make sure this isn't the case; in pratice I let the build spin for one hour (60 minutes) before I can conclude I have reproduced the problem. Needless to say, this doe not help testcase reduction either.

Reproducible on Xcode 13.2 beta, for what it’s worth.

Reproducible on Xcode 13.2 beta 2, for what it's worth.

Still reproducible on Xcode 13.2.1 (13C100)

Breakthrough! I have figured out the bug occurs in a specific situation: when a function that actually captures state refers to itself in a non-escaping manner (e.g. passed as a non-escaping parameter to another function); the function may also need to be async, but that I have no way of knowing.

• I know the function needs to actually capture state to reproduce the issue because there is no issue with function iteratePossibleLeftNodesFakeDispatchAsync(), which is also async and also refers to itself in a non-escaping manner, but does not actually capture state (it is top level).

• I know the function needs to refer to itself in a non-escaping manner, because there is no issue with function iteratePossibleLeftNodes(), which is also async and also captures state, but refers to itself only in an escaping manner.

And why do I know the issue is not with these functions? Because I found a workaround that I only needed to apply to function iteratePossibleLeftNodesDispatch(), which matched the description before I applied the workaround. The workaround, such as it is, consists of creating a iteratePossibleLeftNodesDispatchLoop15() that refers to iteratePossibleLeftNodesDispatchLoop14(), a iteratePossibleLeftNodesDispatchLoop14() that refers to iteratePossibleLeftNodesDispatchLoop13(), and so forth, until I get to iteratePossibleLeftNodesDispatchLoop0() which goes into fatalError rather than refer to anything else. Otherwise, all with identical bodies of course.

In my whole carrier, I can't remember ever having to write so seemingly pointless code in order to satisfy a compiler; and remember I used to write BASIC on the APPLE ][e.

AsyncCountdown.zip

Attaching the latest version of the project so you can look at the workaround in context.

While no one has gotten back to me, I no longer reproduce the issue with Xcode 14.2, so it was fixed some time between 13.2 (excluded) and that version (sorry I can't be more accurate, I haven't been very diligent on checking this issue). If I had to guess, I would say this was fixed by #41826