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Diffstat (limited to 'tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-contravariant.rs')
-rw-r--r-- | tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-contravariant.rs | 36 |
1 files changed, 0 insertions, 36 deletions
diff --git a/tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-contravariant.rs b/tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-contravariant.rs deleted file mode 100644 index 921061916..000000000 --- a/tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-contravariant.rs +++ /dev/null @@ -1,36 +0,0 @@ -// Test a case where variance and higher-ranked types interact in surprising ways. -// -// In particular, we test this pattern in trait solving, where it is not connected -// to any part of the source code. - -trait Trait<T> {} - -fn foo<T>() -where - T: Trait<for<'b> fn(&'b u32)>, -{ -} - -impl<'a> Trait<fn(&'a u32)> for () {} - -fn main() { - // Here, proving that `(): Trait<for<'b> fn(&'b u32)>` uses the impl: - // - // - The impl provides the clause `forall<'a> { (): Trait<fn(&'a u32)> }` - // - We instantiate `'a` existentially to get `(): Trait<fn(&?a u32)>` - // - We unify `fn(&?a u32)` with `for<'b> fn(&'b u32)` -- this does a - // "bidirectional" subtyping check, so we wind up with: - // - `fn(&?a u32) <: for<'b> fn(&'b u32)` :- - // - `&'!b u32 <: &?a u32` - // - `!'b: ?a` -- solveable if `?a` is inferred to `'empty` - // - `for<'b> fn(&'b u32) <: fn(&?a u32)` :- - // - `&?a u32 u32 <: &?b u32` - // - `?a: ?b` -- solveable if `?b` is also inferred to `'empty` - // - So the subtyping check succeeds, somewhat surprisingly. - // This is because we can use `'empty`. - // - // NB. *However*, the reinstated leak-check gives an error here. - - foo::<()>(); - //~^ ERROR implementation of `Trait` is not general enough -} |