Why this kind of isolation pattern is allowed?

Using Swift
,
1

This code is compiled and have no warning.

even though State is shared between different actor which is unSendable and even not makred as sending.


func bar(isolation actor: isolated any Actor = #isolation) async {
    var value = 0

// this is allowed because we are taking copy of Sendable?
    await foo(isolation: MainActor.shared) {
        return 100
    } body: { mutableNumber in
        mutableNumber += 100
        value += 100
    }
    // NonSendable is shared between, MainActor and current Actor
    await foo(isolation: MainActor.shared) {
        return NonSendable()
    } body: { unSendable in
        value += 100
        unSendable.doUnsafe()
        unSendable = NonSendable()
    }
    // mutate TaskGroup from MainActor and current Actor
    await foo2 (isolation: MainActor.shared) { group in
        value += 100
        group.addTask {
            
        }
    }
}


func foo<T:~Copyable>(
    isolation actor: isolated any Actor = #isolation,
    provider: @Sendable () -> sending T,
    body: (inout T) async -> Void
) async ->  Void {
    var ref = provider()
    await body(&ref)
}


func foo2(
    isolation actor: isolated any Actor = #isolation,
    body: (inout TaskGroup<Void>) async -> Void
) async ->  Void {
    await withTaskGroup(of: Void.self) { group in
        // this is actor context
        group.addTask {
            
        }
        // body is caller's context ( actor != caller )
        await body(&group)
    }
   
}


struct NonSendable: ~Copyable { }

@available(*, unavailable)
extension NonSendable: Sendable {
    
}

for now NonSendable state is shared in Swift 6.
At least in the code above there is no data race in runtime.
I think pattern like above could potentionally make data race, or did I miss something?

Above pattern is inspired by new TaskGroup implementation

Edited for to use valid case since Actor instance method somehow not works

2

Still xcode 16 beta 4 prevents this kind of pattern partially. (not fully!)

func bar(isolation actor: isolated any Actor = #isolation) async {
    var value = 0

// this is allowed because we are taking copy of Sendable?
    await foo(isolation: MainActor.shared) {
        return 100
    } body: { mutableNumber in
     /// why this is allowd?
        mutableNumber += 100
        value += 100
    }
    // NonSendable is shared between, MainActor and current Actor
    await foo(isolation: MainActor.shared) {
        return NonSendable()
    } body: { unSendable in
        value += 100
        unSendable.doUnsafe()
        unSendable = NonSendable()
    }
    // taskGroup is created from MainActor and passed to #actor ?
    await foo2 (isolation: MainActor.shared) { group in
        value += 100
///Sending 'actor'-isolated value of type '(inout TaskGroup<Void>) async -> Void' with later accesses to main actor-isolated context risks causing data races
        let _ = actor
        group.addTask {
            
        }
    }
}

parameter of foo2 is protected by the MainActor. but local mutable variable value which is isolated to the actor can be accessed within MainActor without any error.