src/test/ui/regions/regions-trait-object-subtyping.rs

   1 // revisions: base nll
   2 // ignore-compare-mode-nll
   3 //[nll] compile-flags: -Z borrowck=mir
   4
   5 trait Dummy { fn dummy(&self); }
   6
   7 fn foo1<'a:'b,'b>(x: &'a mut (dyn Dummy+'a)) -> &'b mut (dyn Dummy+'b) {
   8     // Here, we are able to coerce
   9     x
  10 }
  11
  12 fn foo2<'a:'b,'b>(x: &'b mut (dyn Dummy+'a)) -> &'b mut (dyn Dummy+'b) {
  13     // Here, we are able to coerce
  14     x
  15 }
  16
  17 fn foo3<'a,'b>(x: &'a mut dyn Dummy) -> &'b mut dyn Dummy {
  18     // Without knowing 'a:'b, we can't coerce
  19     x
  20     //[base]~^ ERROR lifetime bound not satisfied
  21     //[base]~| ERROR cannot infer an appropriate lifetime
  22     //[nll]~^^^ ERROR lifetime may not live long enough
  23 }
  24
  25 struct Wrapper<T>(T);
  26 fn foo4<'a:'b,'b>(x: Wrapper<&'a mut dyn Dummy>) -> Wrapper<&'b mut dyn Dummy> {
  27     // We can't coerce because it is packed in `Wrapper`
  28     x
  29     //[base]~^ ERROR mismatched types
  30     //[nll]~^^ ERROR lifetime may not live long enough
  31 }
  32
  33 fn main() {}