src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unrelated.rs

   1 // edition:2018
   2
   3 trait Trait<'a, 'b> {}
   4 impl<T> Trait<'_, '_> for T {}
   5
   6 // `Ordinary<'a> <: Ordinary<'b>` if `'a: 'b`, as with most types.
   7 //
   8 // I am purposefully avoiding the terms co- and contra-variant because
   9 // their application to regions depends on how you interpreted Rust
  10 // regions. -nikomatsakis
  11 struct Ordinary<'a>(&'a u8);
  12
  13 // Here we get an error because none of our choices (either `'d` nor `'e`) are outlived
  14 // by both `'a` and `'b`.
  15
  16 fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'d, 'e>
  17 //~^ ERROR hidden type for `impl Trait` captures lifetime that does not appear in bounds
  18 where
  19     'a: 'e,
  20     'b: 'd,
  21 {
  22     // Hidden type `Ordinary<'0>` with constraints:
  23     //
  24     // ```
  25     // 'a: '0
  26     // 'b: '0
  27     // 'a in ['d, 'e]
  28     // ```
  29     if condition() { a } else { b }
  30 }
  31
  32 fn condition() -> bool {
  33     true
  34 }
  35
  36 fn main() {}