Remove Sendability from all Iterators (#219)

FranzBusch · tcldr · commit 3b8967d664e6 · 2022-11-03T15:27:08.000Z
# Motivation
We have been discussing this a lot in the other PRs, but in general said that an `AsyncIterator` is the connection between the consuming task and the `AsyncSequence`. If an `AsyncIterator` would be `Sendable` then we don't have that relationship anymore. Therefore, no iterator of an `AsyncIterator` should be `Sendable`.

# Modification
Remove all `Sendable` conformances of the iterators even the conditional ones. We can always add them back later.
diff --git a/Sources/AsyncAlgorithms/AsyncAlgorithms.docc/Guides/Effects.md b/Sources/AsyncAlgorithms/AsyncAlgorithms.docc/Guides/Effects.md
@@ -1,59 +1,59 @@
 | Type                                                | Throws       | Sendability |
 |-----------------------------------------------------|--------------|-------------|
 | `AsyncAdjacentPairsSequence`                        | rethrows     | Conditional |
-| `AsyncBufferedByteIterator`                         | throws       | Sendable    |
+| `AsyncBufferedByteIterator`                         | throws       | Not Sendable|
 | `AsyncBufferSequence`                               | rethrows     | Conditional |
-| `AsyncBufferSequence.Iterator`                      | rethrows     | Conditional |
+| `AsyncBufferSequence.Iterator`                      | rethrows     | Not Sendable|
 | `AsyncChain2Sequence`                               | rethrows     | Conditional |
-| `AsyncChain2Sequence.Iterator`                      | rethrows     | Conditional |
+| `AsyncChain2Sequence.Iterator`                      | rethrows     | Not Sendable|
 | `AsyncChain3Sequence`                               | rethrows     | Conditional |
-| `AsyncChain3Sequence.Iterator`                      | rethrows     | Conditional |
+| `AsyncChain3Sequence.Iterator`                      | rethrows     | Not Sendable|
 | `AsyncChannel`                                      | non-throwing | Sendable    |
-| `AsyncChannel.Iterator`                             | non-throwing | Sendable    |
+| `AsyncChannel.Iterator`                             | non-throwing | Not Sendable|
 | `AsyncChunkedByGroupSequence`                       | rethrows     | Conditional |
-| `AsyncChunkedByGroupSequence.Iterator`              | rethrows     | Conditional |
+| `AsyncChunkedByGroupSequence.Iterator`              | rethrows     | Not Sendable|
 | `AsyncChunkedOnProjectionSequence`                  | rethrows     | Conditional |
-| `AsyncChunkedOnProjectionSequence.Iterator`         | rethrows     | Conditional |
+| `AsyncChunkedOnProjectionSequence.Iterator`         | rethrows     | Not Sendable|
 | `AsyncChunksOfCountOrSignalSequence`                | rethrows     | Sendable    |
-| `AsyncChunksOfCountOrSignalSequence.Iterator`       | rethrows     | Sendable    |
+| `AsyncChunksOfCountOrSignalSequence.Iterator`       | rethrows     | Not Sendable|
 | `AsyncChunksOfCountSequence`                        | rethrows     | Conditional |
-| `AsyncChunksOfCountSequence.Iterator`               | rethrows     | Conditional |
+| `AsyncChunksOfCountSequence.Iterator`               | rethrows     | Not Sendable|
 | `AsyncCombineLatest2Sequence`                       | rethrows     | Sendable    |
-| `AsyncCombineLatest2Sequence.Iterator`              | rethrows     | Sendable    |
+| `AsyncCombineLatest2Sequence.Iterator`              | rethrows     | Not Sendable|
 | `AsyncCombineLatest3Sequence`                       | rethrows     | Sendable    |
-| `AsyncCombineLatest3Sequence.Iterator`              | rethrows     | Sendable    |
+| `AsyncCombineLatest3Sequence.Iterator`              | rethrows     | Not Sendable|
 | `AsyncCompactedSequence`                            | rethrows     | Conditional |
-| `AsyncCompactedSequence.Iterator`                   | rethrows     | Conditional |
+| `AsyncCompactedSequence.Iterator`                   | rethrows     | Not Sendable|
 | `AsyncDebounceSequence`                             | rethrows     | Sendable    |
-| `AsyncDebounceSequence.Iterator`                    | rethrows     | Sendable    |
+| `AsyncDebounceSequence.Iterator`                    | rethrows     | Not Sendable|
 | `AsyncExclusiveReductionsSequence`                  | rethrows     | Conditional |
-| `AsyncExclusiveReductionsSequence.Iterator`         | rethrows     | Conditional |
+| `AsyncExclusiveReductionsSequence.Iterator`         | rethrows     | Not Sendable|
 | `AsyncInclusiveReductionsSequence`                  | rethrows     | Conditional |
-| `AsyncInclusiveReductionsSequence.Iterator`         | rethrows     | Conditional |
+| `AsyncInclusiveReductionsSequence.Iterator`         | rethrows     | Not Sendable|
 | `AsyncInterspersedSequence`                         | rethrows     | Conditional |
-| `AsyncInterspersedSequence.Iterator`                | rethrows     | Conditional |
+| `AsyncInterspersedSequence.Iterator`                | rethrows     | Not Sendable|
 | `AsyncJoinedSequence`                               | rethrows     | Conditional |
-| `AsyncJoinedSequence.Iterator`                      | rethrows     | Conditional |
+| `AsyncJoinedSequence.Iterator`                      | rethrows     | Not Sendable|
 | `AsyncLazySequence`                                 | non-throwing | Conditional |
-| `AsyncLazySequence.Iterator`                        | non-throwing | Conditional |
+| `AsyncLazySequence.Iterator`                        | non-throwing | Not Sendable|
 | `AsyncLimitBuffer`                                  | non-throwing | Sendable    |
 | `AsyncMerge2Sequence`                               | rethrows     | Sendable    |
-| `AsyncMerge2Sequence.Iterator`                      | rethrows     | Sendable    |
+| `AsyncMerge2Sequence.Iterator`                      | rethrows     | Not Sendable|
 | `AsyncMerge3Sequence`                               | rethrows     | Sendable    |
-| `AsyncMerge3Sequence.Iterator`                      | rethrows     | Sendable    |
+| `AsyncMerge3Sequence.Iterator`                      | rethrows     | Not Sendable|
 | `AsyncRemoveDuplicatesSequence`                     | rethrows     | Conditional |
-| `AsyncRemoveDuplicatesSequence.Iterator`            | rethrows     | Conditional |
+| `AsyncRemoveDuplicatesSequence.Iterator`            | rethrows     | Not Sendable|
 | `AsyncThrottleSequence`                             | rethrows     | Conditional |
-| `AsyncThrottleSequence.Iterator`                    | rethrows     | Conditional |
+| `AsyncThrottleSequence.Iterator`                    | rethrows     | Not Sendable|
 | `AsyncThrowingChannel`                              | throws       | Sendable    |
-| `AsyncThrowingChannel.Iterator`                     | throws       | Sendable    |
+| `AsyncThrowingChannel.Iterator`                     | throws       | Not Sendable|
 | `AsyncThrowingExclusiveReductionsSequence`          | throws       | Conditional |
-| `AsyncThrowingExclusiveReductionsSequence.Iterator` | throws       | Conditional |
+| `AsyncThrowingExclusiveReductionsSequence.Iterator` | throws       | Not Sendable|
 | `AsyncThrowingInclusiveReductionsSequence`          | throws       | Conditional |
-| `AsyncThrowingInclusiveReductionsSequence.Iterator` | throws       | Conditional |
+| `AsyncThrowingInclusiveReductionsSequence.Iterator` | throws       | Not Sendable|
 | `AsyncTimerSequence`                                | non-throwing | Sendable    |
-| `AsyncTimerSequence.Iterator`                       | non-throwing | Sendable    |
+| `AsyncTimerSequence.Iterator`                       | non-throwing | Not Sendable|
 | `AsyncZip2Sequence`                                 | rethrows     | Sendable    |
-| `AsyncZip2Sequence.Iterator`                        | rethrows     | Sendable    |
+| `AsyncZip2Sequence.Iterator`                        | rethrows     | Not Sendable|
 | `AsyncZip3Sequence`                                 | rethrows     | Sendable    |
-| `AsyncZip3Sequence.Iterator`                        | rethrows     | Sendable    |
+| `AsyncZip3Sequence.Iterator`                        | rethrows     | Not Sendable|
diff --git a/Sources/AsyncAlgorithms/AsyncBufferSequence.swift b/Sources/AsyncAlgorithms/AsyncBufferSequence.swift
@@ -235,7 +235,6 @@ public struct AsyncBufferSequence<Base: AsyncSequence, Buffer: AsyncBuffer> wher
 }
 
 extension AsyncBufferSequence: Sendable where Base: Sendable { }
-extension AsyncBufferSequence.Iterator: Sendable where Base: Sendable { }
 
 extension AsyncBufferSequence: AsyncSequence {
   public typealias Element = Buffer.Output
diff --git a/Sources/AsyncAlgorithms/AsyncChain3Sequence.swift b/Sources/AsyncAlgorithms/AsyncChain3Sequence.swift
@@ -95,4 +95,3 @@ extension AsyncChain3Sequence: AsyncSequence {
 }
 
 extension AsyncChain3Sequence: Sendable where Base1: Sendable, Base2: Sendable, Base3: Sendable { }
-extension AsyncChain3Sequence.Iterator: Sendable where Base1.AsyncIterator: Sendable, Base2.AsyncIterator: Sendable, Base3.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncCompactedSequence.swift b/Sources/AsyncAlgorithms/AsyncCompactedSequence.swift
@@ -69,4 +69,3 @@ extension AsyncSequence {
 }
 
 extension AsyncCompactedSequence: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
-extension AsyncCompactedSequence.Iterator: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncExclusiveReductionsSequence.swift b/Sources/AsyncAlgorithms/AsyncExclusiveReductionsSequence.swift
@@ -112,4 +112,3 @@ extension AsyncExclusiveReductionsSequence: AsyncSequence {
 }
 
 extension AsyncExclusiveReductionsSequence: Sendable where Base: Sendable, Element: Sendable { }
-extension AsyncExclusiveReductionsSequence.Iterator: Sendable where Base.AsyncIterator: Sendable, Element: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncInclusiveReductionsSequence.swift b/Sources/AsyncAlgorithms/AsyncInclusiveReductionsSequence.swift
@@ -85,4 +85,3 @@ extension AsyncInclusiveReductionsSequence: AsyncSequence {
 }
 
 extension AsyncInclusiveReductionsSequence: Sendable where Base: Sendable { }
-extension AsyncInclusiveReductionsSequence.Iterator: Sendable where Base.AsyncIterator: Sendable, Base.Element: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncInterspersedSequence.swift b/Sources/AsyncAlgorithms/AsyncInterspersedSequence.swift
@@ -100,5 +100,3 @@ extension AsyncInterspersedSequence: AsyncSequence {
 }
 
 extension AsyncInterspersedSequence: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
-extension AsyncInterspersedSequence.Iterator: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
-extension AsyncInterspersedSequence.Iterator.State: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncJoinedBySeparatorSequence.swift b/Sources/AsyncAlgorithms/AsyncJoinedBySeparatorSequence.swift
@@ -142,9 +142,3 @@ public struct AsyncJoinedBySeparatorSequence<Base: AsyncSequence, Separator: Asy
 
 extension AsyncJoinedBySeparatorSequence: Sendable
 where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Separator: Sendable { }
-extension AsyncJoinedBySeparatorSequence.Iterator: Sendable
-where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Base.AsyncIterator: Sendable, Separator: Sendable, Separator.AsyncIterator: Sendable, Base.Element.AsyncIterator: Sendable { }
-extension AsyncJoinedBySeparatorSequence.Iterator.State: Sendable
-where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Base.AsyncIterator: Sendable, Separator: Sendable, Separator.AsyncIterator: Sendable, Base.Element.AsyncIterator: Sendable { }
-extension AsyncJoinedBySeparatorSequence.Iterator.State.SeparatorState: Sendable
-where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Base.AsyncIterator: Sendable, Separator: Sendable, Separator.AsyncIterator: Sendable, Base.Element.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncJoinedSequence.swift b/Sources/AsyncAlgorithms/AsyncJoinedSequence.swift
@@ -92,7 +92,3 @@ public struct AsyncJoinedSequence<Base: AsyncSequence>: AsyncSequence where Base
 
 extension AsyncJoinedSequence: Sendable
 where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Base.AsyncIterator: Sendable, Base.Element.AsyncIterator: Sendable { }
-extension AsyncJoinedSequence.Iterator: Sendable
-where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Base.AsyncIterator: Sendable, Base.Element.AsyncIterator: Sendable { }
-extension AsyncJoinedSequence.Iterator.State: Sendable
-where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Base.AsyncIterator: Sendable, Base.Element.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncLazySequence.swift b/Sources/AsyncAlgorithms/AsyncLazySequence.swift
@@ -67,4 +67,3 @@ public struct AsyncLazySequence<Base: Sequence>: AsyncSequence {
 }
 
 extension AsyncLazySequence: Sendable where Base: Sendable { }
-extension AsyncLazySequence.Iterator: Sendable where Base.Iterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncRemoveDuplicatesSequence.swift b/Sources/AsyncAlgorithms/AsyncRemoveDuplicatesSequence.swift
@@ -86,7 +86,6 @@ public struct AsyncRemoveDuplicatesSequence<Base: AsyncSequence>: AsyncSequence
 }
 
 extension AsyncRemoveDuplicatesSequence: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
-extension AsyncRemoveDuplicatesSequence.Iterator: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
 
 
 /// An asynchronous sequence that omits repeated elements by testing them with an error-throwing predicate.
@@ -145,4 +144,3 @@ public struct AsyncThrowingRemoveDuplicatesSequence<Base: AsyncSequence>: AsyncS
 }
 
 extension AsyncThrowingRemoveDuplicatesSequence: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
-extension AsyncThrowingRemoveDuplicatesSequence.Iterator: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncThrottleSequence.swift b/Sources/AsyncAlgorithms/AsyncThrottleSequence.swift
@@ -102,6 +102,3 @@ extension AsyncThrottleSequence: AsyncSequence {
 
 @available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
 extension AsyncThrottleSequence: Sendable where Base: Sendable, Element: Sendable { }
-
-@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
-extension AsyncThrottleSequence.Iterator: Sendable where Base.AsyncIterator: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncThrowingExclusiveReductionsSequence.swift b/Sources/AsyncAlgorithms/AsyncThrowingExclusiveReductionsSequence.swift
@@ -119,4 +119,3 @@ extension AsyncThrowingExclusiveReductionsSequence: AsyncSequence {
 }
 
 extension AsyncThrowingExclusiveReductionsSequence: Sendable where Base: Sendable, Element: Sendable { }
-extension AsyncThrowingExclusiveReductionsSequence.Iterator: Sendable where Base.AsyncIterator: Sendable, Element: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncThrowingInclusiveReductionsSequence.swift b/Sources/AsyncAlgorithms/AsyncThrowingInclusiveReductionsSequence.swift
@@ -89,4 +89,3 @@ extension AsyncThrowingInclusiveReductionsSequence: AsyncSequence {
 }
 
 extension AsyncThrowingInclusiveReductionsSequence: Sendable where Base: Sendable { }
-extension AsyncThrowingInclusiveReductionsSequence.Iterator: Sendable where Base.AsyncIterator: Sendable, Base.Element: Sendable { }
diff --git a/Sources/AsyncAlgorithms/AsyncTimerSequence.swift b/Sources/AsyncAlgorithms/AsyncTimerSequence.swift
@@ -89,6 +89,3 @@ extension AsyncTimerSequence where C == SuspendingClock {
 
 @available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
 extension AsyncTimerSequence: Sendable { }
-
-@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
-extension AsyncTimerSequence.Iterator: Sendable { }
diff --git a/Tests/AsyncAlgorithmsTests/Support/GatedSequence.swift b/Tests/AsyncAlgorithmsTests/Support/GatedSequence.swift
@@ -52,4 +52,3 @@ extension GatedSequence: AsyncSequence {
 }
 
 extension GatedSequence: Sendable where Element: Sendable { }
-extension GatedSequence.Iterator: Sendable where Element: Sendable { }

Original file line number	Diff line number	Diff line change
`@@ -235,7 +235,6 @@ public struct AsyncBufferSequence<Base: AsyncSequence, Buffer: AsyncBuffer> wher`
`235`	`235`	`}`
`236`	`236`
`237`	`237`	`extension AsyncBufferSequence: Sendable where Base: Sendable { }`
`238`		`-extension AsyncBufferSequence.Iterator: Sendable where Base: Sendable { }`
`239`	`238`
`240`	`239`	`extension AsyncBufferSequence: AsyncSequence {`
`241`	`240`	`public typealias Element = Buffer.Output`
Original file line number	Diff line number	Diff line change
`@@ -95,4 +95,3 @@ extension AsyncChain3Sequence: AsyncSequence {`
`95`	`95`	`}`
`96`	`96`
`97`	`97`	`extension AsyncChain3Sequence: Sendable where Base1: Sendable, Base2: Sendable, Base3: Sendable { }`
`98`		`-extension AsyncChain3Sequence.Iterator: Sendable where Base1.AsyncIterator: Sendable, Base2.AsyncIterator: Sendable, Base3.AsyncIterator: Sendable { }`
Original file line number	Diff line number	Diff line change
`@@ -69,4 +69,3 @@ extension AsyncSequence {`
`69`	`69`	`}`
`70`	`70`
`71`	`71`	`extension AsyncCompactedSequence: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }`
`72`		`-extension AsyncCompactedSequence.Iterator: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }`
Original file line number	Diff line number	Diff line change
`@@ -112,4 +112,3 @@ extension AsyncExclusiveReductionsSequence: AsyncSequence {`
`112`	`112`	`}`
`113`	`113`
`114`	`114`	`extension AsyncExclusiveReductionsSequence: Sendable where Base: Sendable, Element: Sendable { }`
`115`		`-extension AsyncExclusiveReductionsSequence.Iterator: Sendable where Base.AsyncIterator: Sendable, Element: Sendable { }`
Original file line number	Diff line number	Diff line change
`@@ -85,4 +85,3 @@ extension AsyncInclusiveReductionsSequence: AsyncSequence {`
`85`	`85`	`}`
`86`	`86`
`87`	`87`	`extension AsyncInclusiveReductionsSequence: Sendable where Base: Sendable { }`
`88`		`-extension AsyncInclusiveReductionsSequence.Iterator: Sendable where Base.AsyncIterator: Sendable, Base.Element: Sendable { }`
Original file line number	Diff line number	Diff line change
`@@ -100,5 +100,3 @@ extension AsyncInterspersedSequence: AsyncSequence {`
`100`	`100`	`}`
`101`	`101`
`102`	`102`	`extension AsyncInterspersedSequence: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }`
`103`		`-extension AsyncInterspersedSequence.Iterator: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }`
`104`		`-extension AsyncInterspersedSequence.Iterator.State: Sendable where Base: Sendable, Base.Element: Sendable, Base.AsyncIterator: Sendable { }`
Original file line number	Diff line number	Diff line change
`@@ -67,4 +67,3 @@ public struct AsyncLazySequence<Base: Sequence>: AsyncSequence {`
`67`	`67`	`}`
`68`	`68`
`69`	`69`	`extension AsyncLazySequence: Sendable where Base: Sendable { }`
`70`		`-extension AsyncLazySequence.Iterator: Sendable where Base.Iterator: Sendable { }`