incorrect warning "'nonisolated(unsafe)' has no effect on property, consider using 'nonisolated'"

[lukaskollmer]

Description

the program below compiles fine, but with a warning saying that "'nonisolated(unsafe)' has no effect on property 'value', consider using 'nonisolated'".

this is false: replacing the nonisolated(unsafe) with just nonisolated will result in the compiler (correctly) rejecting the program.

Reproduction

import Observation

@Observable
final class Foo: Sendable {
    nonisolated(unsafe) var value: Int? // warning: 'nonisolated(unsafe)' has no effect on property 'value', consider using 'nonisolated'
}

Expected behavior

the compiler should not emit this warning for this program

Environment

swift-driver version: 1.120.5 Apple Swift version 6.1.2 (swiftlang-6.1.2.1.2 clang-1700.0.13.5)
Target: arm64-apple-macosx15.0

Additional information

removing the @Observable macro causes the warning to disappear