Comment by Michael Verges (JIRA)

It seems the intended behavior of functions declared 'rethrows' is to only propagate Errors thrown from the parameter. The parameter '_ fs' is an array, not a closure, so the rethrowing function is not responsible for error handling.

Here is a more explicit example:

struct Unit: Error {}

class Alpha {
    func foo() throws {
        throw Unit()
    }
}

func bar(function: () throws -> Void, alpha: Alpha) rethrows {
    try alpha.foo()
    // ERROR: Call can throw, but the error is not handled; a function declared 'rethrows' may only throw if its parameter does
}

Maybe this bug should be resolved by better diagnosing, like in my example where it explicitly states "a function declared 'rethrows' may only throw if its parameter does".

Yeah, I don't think this is supposed to be accepted, as useful as it would be. cc @xedin