rust/tests/ui/nll/ty-outlives/projection-one-region-trait-bound-static-closure.rs
2024-02-16 20:02:50 +00:00

89 lines
2.3 KiB
Rust

// Test cases where we constrain `<T as Anything<'b>>::AssocType` to
// outlive `'static`. In this case, we don't get any errors, and in fact
// we don't even propagate constraints from the closures to the callers.
//@ compile-flags:-Zverbose-internals
//@ check-pass
#![allow(warnings)]
#![feature(rustc_attrs)]
use std::cell::Cell;
trait Anything<'a> {
type AssocType: 'static;
}
fn with_signature<'a, T, F>(cell: Cell<&'a ()>, t: T, op: F)
where
F: FnOnce(Cell<&'a ()>, T),
{
op(cell, t)
}
fn require<'a, 'b, T>(_cell: Cell<&'a ()>, _t: T)
where
T: Anything<'b>,
T::AssocType: 'a,
{
}
#[rustc_regions]
fn no_relationships_late<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
where
T: Anything<'b>,
{
with_signature(cell, t, |cell, t| require(cell, t));
}
#[rustc_regions]
fn no_relationships_early<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
where
T: Anything<'b>,
'a: 'a,
{
with_signature(cell, t, |cell, t| require(cell, t));
}
#[rustc_regions]
fn projection_outlives<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
where
T: Anything<'b>,
T::AssocType: 'a,
{
// This error is unfortunate. This code ought to type-check: we
// are projecting `<T as Anything<'b>>::AssocType`, and we know
// that this outlives `'a` because of the where-clause. However,
// the way the region checker works, we don't register this
// outlives obligation, and hence we get an error: this is because
// what we see is a projection like `<T as
// Anything<'?0>>::AssocType`, and we don't yet know if `?0` will
// equal `'b` or not, so we ignore the where-clause. Obviously we
// can do better here with a more involved verification step.
with_signature(cell, t, |cell, t| require(cell, t));
}
#[rustc_regions]
fn elements_outlive<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
where
T: Anything<'b>,
'b: 'a,
{
with_signature(cell, t, |cell, t| require(cell, t));
}
#[rustc_regions]
fn one_region<'a, T>(cell: Cell<&'a ()>, t: T)
where
T: Anything<'a>,
{
// Note that in this case the closure still propagates an external
// requirement between two variables in its signature, but the
// creator maps both those two region variables to `'a` on its
// side.
with_signature(cell, t, |cell, t| require(cell, t));
}
fn main() {}