Teach #isolation to respect the flow-sensitive nature of actor initializers
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…ializers Actor initializers have a flow-sensitive property where they are isolated to the actor being initialized only after the actor instance itself is fully-initialized. However, this behavior was not being reflected in the expansion of `#isolation`, which was always expanding to `self`, even before `self` is fully formed. This led to a source compatibility issue with code that used the async for..in loop within an actor initializer *prior* to the point where the actor was fully initialized, because the type checker is introducing the `#isolation` (SE-0421) but Definite Initialization properly rejects the use of `self` before it is initialized. Address this issue by delaying the expansion of `#isolation` until after the actor is fully initialized. In SILGen, we introduce a new builtin for this case (and *just* this case) called `flowSensitiveSelfIsolation`, which takes in `self` as its argument and produces an `(any Actor)?`. Definite initialization does not treat this as a use of `self`. Rather, it tracks these builtins and replaces them either with `self` (if it is fully-initialized at this point) or `nil` (if it is not fully-initialized at this point), mirroring the flow-sensitive isolation semantics described in SE-0327. Fixes rdar://127080037.
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Distributed actors can be treated as actors by accessing the `asLocalActor` property. When lowering `#isolation` in a distributed actor initializer, use a separate builtin `flowSensitiveDistributedSelfIsolation` to capture the conformance to `DistributedActor`, and have Definite Initialization introduce the call to the `asLocalActor` getter when needed.
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Actor initializers have a flow-sensitive property where they are isolated to the actor being initialized only after the actor instance itself is fully-initialized. However, this behavior was not being reflected in the expansion of
#isolation, which was always expanding toself, even beforeselfis fully formed.This led to a source compatibility issue with code that used the async for..in loop within an actor initializer prior to the point where the actor was fully initialized, because the type checker is introducing the
#isolation(SE-0421) but Definite Initialization properly rejects the use ofselfbefore it is initialized.Address this issue by delaying the expansion of
#isolationuntil after the actor is fully initialized. In SILGen, we introduce a new builtin for this case (and just this case) calledflowSensitiveSelfIsolation, which takes inselfas its argument and produces an(any Actor)?. Definite initialization does not treat this as a use ofself. Rather, it tracks these builtins and replaces them either withself(if it is fully-initialized at this point) ornil(if it is not fully-initialized at this point), mirroring the flow-sensitive isolation semantics described in SE-0327.Fixes rdar://127080037.