src/test/ui/span/dropck-object-cycle.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // This test used to be part of a run-pass test, but revised outlives
  12 // rule means that it no longer compiles.
  13
  14 #![allow(unused_variables)]
  15
  16 trait Trait<'a> {
  17     fn long(&'a self) -> isize;
  18     fn short<'b>(&'b self) -> isize;
  19 }
  20
  21 fn object_invoke1<'d>(x: &'d Trait<'d>) -> (isize, isize) { loop { } }
  22
  23 trait MakerTrait {
  24     fn mk() -> Self;
  25 }
  26
  27 fn make_val<T:MakerTrait>() -> T {
  28     MakerTrait::mk()
  29 }
  30
  31 impl<'t> MakerTrait for Box<Trait<'t>+'static> {
  32     fn mk() -> Box<Trait<'t>+'static> { loop { } }
  33 }
  34
  35 pub fn main() {
  36     let m : Box<Trait+'static> = make_val();
  37     assert_eq!(object_invoke1(&*m), (4,5));
  38     //~^ NOTE borrow occurs here
  39
  40     // the problem here is that the full type of `m` is
  41     //
  42     //   Box<Trait<'m>+'static>
  43     //
  44     // Here `'m` must be exactly the lifetime of the variable `m`.
  45     // This is because of two requirements:
  46     // 1. First, the basic type rules require that the
  47     //    type of `m`'s value outlives the lifetime of `m`. This puts a lower
  48     //    bound `'m`.
  49     //
  50     // 2. Meanwhile, the signature of `object_invoke1` requires that
  51     //    we create a reference of type `&'d Trait<'d>` for some `'d`.
  52     //    `'d` cannot outlive `'m`, so that forces the lifetime to be `'m`.
  53     //
  54     // This then conflicts with the dropck rules, which require that
  55     // the type of `m` *strictly outlives* `'m`. Hence we get an
  56     // error.
  57 }
  58 //~^ ERROR `*m` does not live long enough
  59 //~| NOTE `*m` dropped here while still borrowed
  60 //~| NOTE values in a scope are dropped in the opposite order they are created
  61