Remove Sendable constraint for AsyncChain2Sequence (apple#213)

FranzBusch · web-flow · commit be681c12e3a4 · 2022-10-14T08:41:25.000-07:00
# Motivation
We want to remove any `Sendable` constraints on iterators since they ought to not be passed between `Task`s.

# Modification
Explicitly mark the `AsyncChain2Sequence` to be not `Sendable`.

# Result
Nobody can make this `Sendable`.
diff --git a/Sources/AsyncAlgorithms/AsyncChain2Sequence.swift b/Sources/AsyncAlgorithms/AsyncChain2Sequence.swift
@@ -80,4 +80,6 @@ extension AsyncChain2Sequence: AsyncSequence {
 }
 
 extension AsyncChain2Sequence: Sendable where Base1: Sendable, Base2: Sendable { }
-extension AsyncChain2Sequence.Iterator: Sendable where Base1.AsyncIterator: Sendable, Base2.AsyncIterator: Sendable { }
+
+@available(*, unavailable)
+extension AsyncChain2Sequence.Iterator: Sendable { }

Original file line number	Diff line number	Diff line change
`@@ -80,4 +80,6 @@ extension AsyncChain2Sequence: AsyncSequence {`
`80`	`80`	`}`
`81`	`81`
`82`	`82`	`extension AsyncChain2Sequence: Sendable where Base1: Sendable, Base2: Sendable { }`
`83`		`-extension AsyncChain2Sequence.Iterator: Sendable where Base1.AsyncIterator: Sendable, Base2.AsyncIterator: Sendable { }`
	`83`	`+`
	`84`	`+@available(*, unavailable)`
	`85`	`+extension AsyncChain2Sequence.Iterator: Sendable { }`