Build failure with swift-nightly-main: region-isolation errors in MultiProducerSingleConsumerAsyncChannel

[sebsto]

swift-async-algorithms 1.1.3 fails to compile with the current swift-nightly-main toolchain.

All errors are in MultiProducerSingleConsumerAsyncChannel+Internal.swift and look like this:

error: '$0.enqueueContinuation' cannot be returned
note: returning '$0.enqueueContinuation' risks concurrent access to 'inout sending' parameter '$0'
      as caller assumes '$0' and result can be sent to different isolation domains

Same pattern repeats for enqueueProducer, cancelProducer, finish, next, suspendNext, and cancelNext.

To reproduce:

docker run --rm swiftlang/swift:nightly-main-jammy \
  bash -cl "git clone https://github.com/apple/swift-async-algorithms.git && cd swift-async-algorithms && swift build"

Looks like the nightly compiler tightened region-isolation checks around values returned from Mutex.withLock closures that use inout sending parameters.

[sebsto]

This was caught by our CI at awslabs/swift-aws-lambda-runtime#668

[NotTheNHK]

This should be fixed with #419.