mirror
/
rustc-dev-guide
mirror of https://github.com/rust-lang/rustc-dev-guide.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

consider `explicit_implied_const_bounds`

This commit is contained in:
Deadbeef 2025-03-08 16:38:44 +08:00
parent 4f88394545
commit 79e42cfb0b
1 changed files with 30 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
src/effects.md
View File

@ -112,6 +112,34 @@ are revalidated again in [`Checker::revalidate_conditional_constness`].
[`wfcheck::check_impl`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir_analysis/check/wfcheck/fn.check_impl.html
[`Checker::revalidate_conditional_constness`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_const_eval/check_consts/check/struct.Checker.html#method.revalidate_conditional_constness
## `explicit_implied_const_bounds` on associated types and traits
Bounds on associated types, opaque types, and supertraits such as
```rust
trait Foo: ~const PartialEq {
type X: ~const PartialEq;
}
fn foo() -> impl ~const PartialEq {
// ^ unimplemented syntax
}
```
Have their bounds represented differently. Unlike `const_conditions` which need
to be proved for callers, and can be assumed inside the definition (e.g. trait
bounds on functions), these bounds need to be proved at definition (at the impl,
or when returning the opaque) but can be assumed for callers. The non-const
equivalent of these bounds are called [`explicit_item_bounds`].
These bounds are checked in [`compare_impl_item::check_type_bounds`] for HIR
typeck, [`evaluate_host_effect_from_item_bounds`] in the old solver and
[`consider_additional_alias_assumptions`] in the new solver.
[`explicit_item_bounds`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html#method.explicit_item_bounds
[`compare_impl_item::check_type_bounds`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir_analysis/check/compare_impl_item/fn.check_type_bounds.html
[`evaluate_host_effect_from_item_bounds`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/traits/effects/fn.evaluate_host_effect_from_item_bounds.html
[`consider_additional_alias_assumptions`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_next_trait_solver/solve/assembly/trait.GoalKind.html#tymethod.consider_additional_alias_assumptions
## Proving `HostEffectPredicate`s
`HostEffectPredicate`s are implemented both in the [old solver] and the [new
@ -120,7 +148,8 @@ these conditions are met:
* The predicate can be assumed from caller bounds;
* The type has a `const` `impl` for the trait, *and* that const conditions on
the impl holds; or
the impl holds, *and* that the `explicit_implied_const_bounds` on the trait
holds; or
* The type has a built-in implementation for the trait in const contexts. For
example, `Fn` may be implemented by function items if their const conditions
are satisfied, or `Destruct` is implemented in const contexts if the type can