1fd13fddba
After reviewing all tests with `?Sized` and discussing with lcnr, these tests seem like they could probably benefit from `#![rustc_no_implicit_bounds]`.
72 lines
1.8 KiB
Rust
72 lines
1.8 KiB
Rust
//@ compile-flags: -Znext-solver
|
|
//@ check-pass
|
|
#![feature(rustc_attrs)]
|
|
#![rustc_no_implicit_bounds]
|
|
|
|
// A test showcasing that using a provisional cache can differ
|
|
// from only tracking stack entries.
|
|
//
|
|
// Without a provisional cache, we have the following proof tree:
|
|
//
|
|
// - (): A
|
|
// - (): B
|
|
// - (): A (coinductive cycle)
|
|
// - (): C
|
|
// - (): B (coinductive cycle)
|
|
// - (): C
|
|
// - (): B
|
|
// - (): A (coinductive cycle)
|
|
// - (): C (coinductive cycle)
|
|
//
|
|
// While with the current provisional cache implementation we get:
|
|
//
|
|
// - (): A
|
|
// - (): B
|
|
// - (): A (coinductive cycle)
|
|
// - (): C
|
|
// - (): B (coinductive cycle)
|
|
// - (): C
|
|
// - (): B (provisional cache hit)
|
|
//
|
|
// Note that if even if we were to expand the provisional cache hit,
|
|
// the proof tree would still be different:
|
|
//
|
|
// - (): A
|
|
// - (): B
|
|
// - (): A (coinductive cycle)
|
|
// - (): C
|
|
// - (): B (coinductive cycle)
|
|
// - (): C
|
|
// - (): B (provisional cache hit, expanded)
|
|
// - (): A (coinductive cycle)
|
|
// - (): C
|
|
// - (): B (coinductive cycle)
|
|
//
|
|
// Theoretically, this can result in observable behavior differences
|
|
// due to incompleteness. However, this would require a very convoluted
|
|
// example and would still be sound. The difference is determinstic
|
|
// and can not be observed outside of the cycle itself as we don't move
|
|
// non-root cycle participants into the global cache.
|
|
//
|
|
// For an example of how incompleteness could impact the observable behavior here, see
|
|
//
|
|
// tests/ui/traits/next-solver/cycles/coinduction/incompleteness-unstable-result.rs
|
|
#[rustc_coinductive]
|
|
trait A {}
|
|
|
|
#[rustc_coinductive]
|
|
trait B {}
|
|
|
|
#[rustc_coinductive]
|
|
trait C {}
|
|
|
|
impl<T: B + C> A for T {}
|
|
impl<T: A + C> B for T {}
|
|
impl<T: B> C for T {}
|
|
|
|
fn impls_a<T: A>() {}
|
|
|
|
fn main() {
|
|
impls_a::<()>();
|
|
}
|