References to local variables are considered to need dropping if a local variable does

[tmiasko]

For example, function f is rejected with an error that a needs dropping, while g succeeds even though it should use more conservative qualification because it uses an opaque function id:

pub const fn id<T>(t: T) -> T { t }

pub const fn f() -> String {
    let s = String::new();
    let mut a: (Option<String>, Option<&String>) = (None, None);
    a.1 = Some(&s);
    s
}

pub const fn g() -> String {
    let s = String::new();
    let mut a: (Option<String>, Option<&String>) = (None, None);
    a.1 = Some(id(&s));
    s
}

@rustbot label +A-const-eval +A-const-fn

[oli-obk]

I guess the needs drop flag should not be carried through Rvalue::Ref?