Error type access level not enforced for property getters

[lawrence-forooghian]

Description

Given a protocol that has a property getter which throws a typed error, the compiler does not check whether the access level of the error type is compatible with that of the protocol.

Reproduction

internal enum MyError: Error {}

public protocol MyProtocol {
    var foo: String { get throws(MyError) }
}

Expected behavior

I expected a compiler error telling me that the property cannot be declared public because its thrown error uses an internal type. However, instead the code compiles without error.

If I switch the property to a function, then I get the expected error:

internal enum MyError: Error {}

public protocol MyProtocol {
    func bar() throws(MyError) -> String
}

gives "method cannot be declared public because its thrown error uses an internal type".

Environment

Tried with the following:

Xcode 16.1:

swift-driver version: 1.115 Apple Swift version 6.0.2 (swiftlang-6.0.2.1.2 clang-1600.0.26.4)
Target: arm64-apple-macosx15.0

Xcode 16.3 Beta 2:

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.109.103 clang-1700.0.13.2)
Target: arm64-apple-macosx15.0

Additional information

No response