diff options
Diffstat (limited to 'tests/ui/traits/new-solver/alias-bound-preference.rs')
-rw-r--r-- | tests/ui/traits/new-solver/alias-bound-preference.rs | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/tests/ui/traits/new-solver/alias-bound-preference.rs b/tests/ui/traits/new-solver/alias-bound-preference.rs new file mode 100644 index 000000000..e4e0f634e --- /dev/null +++ b/tests/ui/traits/new-solver/alias-bound-preference.rs @@ -0,0 +1,39 @@ +// revisions: old next +//[next] compile-flags: -Ztrait-solver=next +// run-pass + +// A test for https://github.com/rust-lang/trait-system-refactor-initiative/issues/45. + +trait Trait { + type Assoc: Into<u32>; +} +impl<T: Into<u32>> Trait for T { + type Assoc = T; +} +fn prefer_alias_bound_projection<T: Trait>(x: T::Assoc) { + // There are two possible types for `x`: + // - `u32` by using the "alias bound" of `<T as Trait>::Assoc` + // - `<T as Trait>::Assoc`, i.e. `u16`, by using `impl<T> From<T> for T` + // + // We infer the type of `x` to be `u32` here as it is highly likely + // that this is expected by the user. + let x = x.into(); + assert_eq!(std::mem::size_of_val(&x), 4); +} + +fn impl_trait() -> impl Into<u32> { + 0u16 +} + +fn main() { + // There are two possible types for `x`: + // - `u32` by using the "alias bound" of `impl Into<u32>` + // - `impl Into<u32>`, i.e. `u16`, by using `impl<T> From<T> for T` + // + // We infer the type of `x` to be `u32` here as it is highly likely + // that this is expected by the user. + let x = impl_trait().into(); + assert_eq!(std::mem::size_of_val(&x), 4); + + prefer_alias_bound_projection::<u16>(1); +} |