Struct rustc_infer::infer::outlives::verify::VerifyBoundCx

pub struct VerifyBoundCx<'cx, 'tcx> {
    tcx: TyCtxt<'tcx>,
    region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
    implicit_region_bound: Option<Region<'tcx>>,
    param_env: ParamEnv<'tcx>,
}

The TypeOutlives struct has the job of “lowering” a T: 'a obligation into a series of 'a: 'b constraints and “verifys”, as described on the module comment. The final constraints are emitted via a “delegate” of type D – this is usually the infcx, which accrues them into the region_obligations code, but for NLL we use something else.

Fields

tcx: TyCtxt<'tcx>

region_bound_pairs: &'cx RegionBoundPairs<'tcx>

implicit_region_bound: Option<Region<'tcx>>

During borrowck, if there are no outlives bounds on a generic parameter T, we assume that T: 'in_fn_body holds.

Outside of borrowck the only way to prove T: '?0 is by setting '?0 to 'empty.

param_env: ParamEnv<'tcx>

Implementations

impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx>

pub fn new(
    tcx: TyCtxt<'tcx>,
    region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
    implicit_region_bound: Option<Region<'tcx>>,
    param_env: ParamEnv<'tcx>
) -> Self

pub fn generic_bound(&self, generic: GenericKind<'tcx>) -> VerifyBound<'tcx>

Returns a “verify bound” that encodes what we know about generic and the regions it outlives.

fn param_bound(&self, param_ty: ParamTy) -> VerifyBound<'tcx>

pub fn projection_approx_declared_bounds_from_env(
    &self,
    projection_ty: ProjectionTy<'tcx>
) -> Vec<Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>

Given a projection like T::Item, searches the environment for where-clauses like T::Item: 'a. Returns the set of regions 'a that it finds.

This is an “approximate” check – it may not find all applicable bounds, and not all the bounds it returns can be relied upon. In particular, this check ignores region identity. So, for example, if we have <T as Trait<'0>>::Item where '0 is a region variable, and the user has <T as Trait<'a>>::Item: 'b in the environment, then the clause from the environment only applies if '0 = 'a, which we don’t know yet. But we would still include 'b in this list.

pub fn projection_declared_bounds_from_trait(
    &self,
    projection_ty: ProjectionTy<'tcx>
) -> impl Iterator<Item = Region<'tcx>> + 'cx + Captures<'tcx>

Searches the where-clauses in scope for regions that projection_ty is known to outlive. Currently requires an exact match.

pub fn projection_bound(
    &self,
    projection_ty: ProjectionTy<'tcx>,
    visited: &mut SsoHashSet<GenericArg<'tcx>>
) -> VerifyBound<'tcx>

fn bound_from_components(
    &self,
    components: &[Component<'tcx>],
    visited: &mut SsoHashSet<GenericArg<'tcx>>
) -> VerifyBound<'tcx>

fn bound_from_single_component(
    &self,
    component: &Component<'tcx>,
    visited: &mut SsoHashSet<GenericArg<'tcx>>
) -> VerifyBound<'tcx>

fn declared_generic_bounds_from_env(
    &self,
    param_ty: ParamTy
) -> Vec<Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>

Searches the environment for where-clauses like G: 'a where G is either some type parameter T or a projection like T::Item. Returns a vector of the 'a bounds it can find.

This is a conservative check – it may not find all applicable bounds, but all the bounds it returns can be relied upon.

fn declared_generic_bounds_from_env_for_erased_ty(
    &self,
    erased_ty: Ty<'tcx>
) -> Vec<Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>

Searches the environment to find all bounds that apply to erased_ty. Obviously these must be approximate – they are in fact both over and and under approximated:

• Over-approximated because we erase regions, so
• Under-approximated because we look for syntactic equality and so for complex types like <T as Foo<fn(&u32, &u32)>>::Item or whatever we may fail to figure out all the subtleties.

In some cases, such as when erased_ty represents a ty::Param, however, the result is precise.

fn declared_projection_bounds_from_trait(
    &self,
    projection_ty: ProjectionTy<'tcx>
) -> impl Iterator<Item = Region<'tcx>> + 'cx + Captures<'tcx>

Given a projection like <T as Foo<'x>>::Bar, returns any bounds declared in the trait definition. For example, if the trait were

trait Foo<'a> {
    type Bar: 'a;
}

then this function would return 'x. This is subject to the limitations around higher-ranked bounds described in region_bounds_declared_on_associated_item.

fn region_bounds_declared_on_associated_item(
    &self,
    assoc_item_def_id: DefId
) -> impl Iterator<Item = Region<'tcx>>

Given the DefId of an associated item, returns any region bounds attached to that associated item from the trait definition.

For example:

trait Foo<'a> {
    type Bar: 'a;
}

If we were given the DefId of Foo::Bar, we would return 'a. You could then apply the substitutions from the projection to convert this into your namespace. This also works if the user writes where <Self as Foo<'a>>::Bar: 'a on the trait. In fact, it works by searching for just such a where-clause.

It will not, however, work for higher-ranked bounds like:

trait Foo<'a, 'b>
where for<'x> <Self as Foo<'x, 'b>>::Bar: 'x
{
    type Bar;
}

This is for simplicity, and because we are not really smart enough to cope with such bounds anywhere.

fn collect_outlives_from_predicate_list(
    &self,
    erased_ty: Ty<'tcx>,
    predicates: impl Iterator<Item = Predicate<'tcx>>
) -> impl Iterator<Item = Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>

Searches through a predicate list for a predicate T: 'a.

Careful: does not elaborate predicates, and just uses == when comparing ty for equality, so ty must be something that does not involve inference variables and where you otherwise want a precise match.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference’s “Type Layout” chapter for details on type layout guarantees.

Size: 32 bytes