src/test/ui/hr-subtype/hr-subtype.rs

   1 // Targeted tests for the higher-ranked subtyping code.
   2
   3 #![feature(rustc_attrs)]
   4 #![allow(dead_code)]
   5
   6 // revisions: bound_a_vs_bound_a
   7 // revisions: bound_a_vs_bound_b
   8 // revisions: bound_inv_a_vs_bound_inv_b
   9 // revisions: bound_co_a_vs_bound_co_b
  10 // revisions: bound_a_vs_free_x
  11 // revisions: free_x_vs_free_x
  12 // revisions: free_x_vs_free_y
  13 // revisions: free_inv_x_vs_free_inv_y
  14 // revisions: bound_a_b_vs_bound_a
  15 // revisions: bound_co_a_b_vs_bound_co_a
  16 // revisions: bound_contra_a_contra_b_ret_co_a
  17 // revisions: bound_co_a_co_b_ret_contra_a
  18 // revisions: bound_inv_a_b_vs_bound_inv_a
  19 // revisions: bound_a_b_ret_a_vs_bound_a_ret_a
  20
  21 fn gimme<T>(_: Option<T>) {}
  22
  23 struct Inv<'a> {
  24     x: *mut &'a u32,
  25 }
  26
  27 struct Co<'a> {
  28     x: fn(&'a u32),
  29 }
  30
  31 struct Contra<'a> {
  32     x: &'a u32,
  33 }
  34
  35 macro_rules! check {
  36     ($rev:ident: ($t1:ty, $t2:ty)) => {
  37         #[cfg($rev)]
  38         fn subtype<'x, 'y: 'x, 'z: 'y>() {
  39             gimme::<$t2>(None::<$t1>);
  40             //[free_inv_x_vs_free_inv_y]~^ ERROR
  41         }
  42
  43         #[cfg($rev)]
  44         fn supertype<'x, 'y: 'x, 'z: 'y>() {
  45             gimme::<$t1>(None::<$t2>);
  46             //[bound_a_vs_free_x]~^ ERROR
  47             //[free_x_vs_free_y]~^^ ERROR
  48             //[bound_inv_a_b_vs_bound_inv_a]~^^^ ERROR
  49             //[bound_a_b_ret_a_vs_bound_a_ret_a]~^^^^ ERROR
  50             //[free_inv_x_vs_free_inv_y]~^^^^^ ERROR
  51             //[bound_a_b_vs_bound_a]~^^^^^^ ERROR mismatched types
  52             //[bound_contra_a_contra_b_ret_co_a]~^^^^^^^ ERROR
  53         }
  54     };
  55 }
  56
  57 // If both have bound regions, they are equivalent, regardless of
  58 // variant.
  59 check! { bound_a_vs_bound_a: (for<'a> fn(&'a u32),
  60 for<'a> fn(&'a u32)) }
  61 check! { bound_a_vs_bound_b: (for<'a> fn(&'a u32),
  62 for<'b> fn(&'b u32)) }
  63 check! { bound_inv_a_vs_bound_inv_b: (for<'a> fn(Inv<'a>),
  64 for<'b> fn(Inv<'b>)) }
  65 check! { bound_co_a_vs_bound_co_b: (for<'a> fn(Co<'a>),
  66 for<'b> fn(Co<'b>)) }
  67
  68 // Bound is a subtype of free.
  69 check! { bound_a_vs_free_x: (for<'a> fn(&'a u32),
  70 fn(&'x u32)) }
  71
  72 // Two free regions are relatable if subtyping holds.
  73 check! { free_x_vs_free_x: (fn(&'x u32),
  74 fn(&'x u32)) }
  75 check! { free_x_vs_free_y: (fn(&'x u32),
  76 fn(&'y u32)) }
  77 check! { free_inv_x_vs_free_inv_y: (fn(Inv<'x>),
  78 fn(Inv<'y>)) }
  79
  80 // Somewhat surprisingly, a fn taking two distinct bound lifetimes and
  81 // a fn taking one bound lifetime can be interchangeable, but only if
  82 // we are co- or contra-variant with respect to both lifetimes.
  83 //
  84 // The reason is:
  85 // - if we are covariant, then 'a and 'b can be set to the call-site
  86 //   intersection;
  87 // - if we are contravariant, then 'a can be inferred to 'static.
  88 check! { bound_a_b_vs_bound_a: (for<'a,'b> fn(&'a u32, &'b u32),
  89 for<'a>    fn(&'a u32, &'a u32)) }
  90 check! { bound_co_a_b_vs_bound_co_a: (for<'a,'b> fn(Co<'a>, Co<'b>),
  91 for<'a>    fn(Co<'a>, Co<'a>)) }
  92 check! { bound_contra_a_contra_b_ret_co_a: (for<'a,'b> fn(Contra<'a>, Contra<'b>) -> Co<'a>,
  93 for<'a>    fn(Contra<'a>, Contra<'a>) -> Co<'a>) }
  94 check! { bound_co_a_co_b_ret_contra_a: (for<'a,'b> fn(Co<'a>, Co<'b>) -> Contra<'a>,
  95 for<'a>    fn(Co<'a>, Co<'a>) -> Contra<'a>) }
  96
  97 // If we make those lifetimes invariant, then the two types are not interchangeable.
  98 check! { bound_inv_a_b_vs_bound_inv_a: (for<'a,'b> fn(Inv<'a>, Inv<'b>),
  99 for<'a>    fn(Inv<'a>, Inv<'a>)) }
 100 check! { bound_a_b_ret_a_vs_bound_a_ret_a: (for<'a,'b> fn(&'a u32, &'b u32) -> &'a u32,
 101 for<'a>    fn(&'a u32, &'a u32) -> &'a u32) }
 102
 103 #[rustc_error]
 104 fn main() {
 105     //[bound_a_vs_bound_a]~^ ERROR fatal error triggered by #[rustc_error]
 106     //[bound_a_vs_bound_b]~^^ ERROR fatal error triggered by #[rustc_error]
 107     //[bound_inv_a_vs_bound_inv_b]~^^^ ERROR fatal error triggered by #[rustc_error]
 108     //[bound_co_a_vs_bound_co_b]~^^^^ ERROR fatal error triggered by #[rustc_error]
 109     //[free_x_vs_free_x]~^^^^^ ERROR fatal error triggered by #[rustc_error]
 110     //[bound_co_a_b_vs_bound_co_a]~^^^^^^ ERROR
 111     //[bound_co_a_co_b_ret_contra_a]~^^^^^^^ ERROR
 112 }