rust/tests/ui/span/issue-24805-dropck-child-has-items-via-parent.rs

// Check that child trait who only has items via its *parent* trait
// does cause dropck to inject extra region constraints.

#![allow(non_camel_case_types)]

trait Parent { fn foo(&self); }
trait Child: Parent { }

impl Parent for i32 { fn foo(&self) { } }
impl<'a> Parent for &'a D_Child<i32> {
    fn foo(&self) {
        println!("accessing child value: {}", self.0);
    }
}

impl Child for i32 { }
impl<'a> Child for &'a D_Child<i32> { }

struct D_Child<T:Child>(T);
impl <T:Child> Drop for D_Child<T> { fn drop(&mut self) { self.0.foo() } }

fn f_child() {
    // `_d` and `d1` are assigned the *same* lifetime by region inference ...
    let (_d, d1);

    d1 = D_Child(1);
    // ... we store a reference to `d1` within `_d` ...
    _d = D_Child(&d1);
    //~^ ERROR `d1` does not live long enough

    // ... dropck *should* complain, because Drop of _d could (and
    // does) access the already dropped `d1` via the `foo` method.
}

fn main() {
    f_child();
}