Why is `self` considered used-after-consume in coroutine accessors?

[rayx (Huan Xiong)]

@CrystDragon

If I didn't do that, there would be a different error, which also confused me:

_modify {
    var wrapper = Wrapper(consume self)  // <- missing reinitialization of closure capture 'wrapper' after consume
    defer {
        self = wrapper.get()
    }

    yield &wrapper
}

It's a limitation of the current implementation, documented in "Noncopyable variables captured by escaping closures" section of SE-0390. The following tests use consuming parameter, instead of non-copyable value, for simplicity. Test 1 is similar to the example in SE-0399. Test 2 emulates your usage.

func test1(x: consuming String) {
    _ = consume x // error: missing reinitialization of inout parameter 'x' after consume while accessing memory
    x = "abc"
    let fn: () -> Void = { print(x) }
    fn()
}

func test2(x: consuming String) {
    let fn: () -> Void = { _ = consume x } // error: missing reinitialization of inout parameter 'x' after consume while accessing memory
    fn()
}

PS: I think "inout parameter" in these error messages are incorrect.
PS2: As non-escaping closure doesn't have this issue, it appears that a variable referenced in defer code is considered captured by an escaping closure (that's my intuition too).