actor's lazy var with closure expression results in isolation error

[mattmassicotte]

Description

I'm honestly not sure I understand exactly what is going on here. And it is possible this is related to #79060

I would expect this code to compile. I also think the diagnostic message could use a little work, but I cannot come up with another scenario that produces the same error.

Reproduction

func doStuff(work: () async -> Int?) -> Int {
	0
}

actor MyActor {
	func action() {
	}

	// error: Actor-isolated default value in a actor-isolated context
	private lazy var bad = doStuff(work: {
		self.action()

		return nil
	})

	private lazy var good = runDoStuff()

	func runDoStuff() -> Int {
		doStuff(work: {
			self.action()

			return nil
		})
	}
}

Expected behavior

It seems to me like these two things should be equivalent, no?

Environment

Apple Swift version 6.1-dev (LLVM a321a98f4e5b06a, Swift 7a0a6e7)
Target: arm64-apple-macosx15.0

Additional information

No response

[mattmassicotte]

Figured something out for the diagnostic: #79077