nonisolated property wrappers

[mattmassicotte]

Motivation

This isn't an area I understand very well. But it seems like nonisolated property wrappers should be possible if the underlying wrapper type is Sendable.

@propertyWrapper
struct Wrapped<T: Sendable>: Sendable {
	var wrappedValue: T

	init(wrappedValue: T) {
		self.wrappedValue = wrappedValue
	}
}

actor MyActor {
	// if you can write this...
	nonisolated var computedValue: Int {
		get {
			0
		}
		set {
			// ... even if it tricky to implement
		}
	}

	// shouldn't you be able to write this
	// if the wrapper is Sendable?
	@Wrapped nonisolated var wrappedValue: Int = 0
}

Proposed solution

I think this code should be accepted. As is, it produces an error:

error: 'nonisolated' is not supported on properties with property wrappers

Alternatives considered

No response

Additional information

No response

[jamieQ]

some historical context of possible relevance:

1. PR comment thread addressing the root problem
2. related forums thread (also links to other related pitches/discussions)

[mattmassicotte]

@jamieQ thank you! Looks like a non-trivial problem :)

[ryanbooker]

I think this issue makes it impossible to conform to AppIntent when your intent has @Parameter or @Dependency properties, and your app target has Swift 6, Strict Concurrency Checking: Complete, and Default Actor Isolation: MainActor set.