pub struct VerifyBoundCx<'cx, 'tcx> {
    tcx: TyCtxt<'tcx>,
    region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
    implicit_region_bound: Option<Region<'tcx>>,
    caller_bounds: &'cx [PolyTypeOutlivesPredicate<'tcx>],
}
Expand description

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.

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§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.

§caller_bounds: &'cx [PolyTypeOutlivesPredicate<'tcx>]

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

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pub fn new( tcx: TyCtxt<'tcx>, region_bound_pairs: &'cx RegionBoundPairs<'tcx>, implicit_region_bound: Option<Region<'tcx>>, caller_bounds: &'cx [PolyTypeOutlivesPredicate<'tcx>] ) -> Self

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pub fn param_or_placeholder_bound(&self, ty: Ty<'tcx>) -> VerifyBound<'tcx>

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pub fn approx_declared_bounds_from_env( &self, alias_ty: AliasTy<'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.

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pub fn alias_bound( &self, alias_ty: AliasTy<'tcx>, visited: &mut SsoHashSet<GenericArg<'tcx>> ) -> VerifyBound<'tcx>

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

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

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fn declared_generic_bounds_from_env( &self, generic_ty: Ty<'tcx> ) -> 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.

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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.

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pub fn declared_bounds_from_definition( &self, alias_ty: AliasTy<'tcx> ) -> impl Iterator<Item = Region<'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;
}

If we were given the DefId of Foo::Bar, we would return 'a. You could then apply the instantiations 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:

```ignore(this does compile today, previously was marked as compile_fail,E0311) 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.

Auto Trait Implementations§

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

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

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impl<'cx, 'tcx> !RefUnwindSafe for VerifyBoundCx<'cx, 'tcx>

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impl<'cx, 'tcx> !Send for VerifyBoundCx<'cx, 'tcx>

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impl<'cx, 'tcx> !Sync for VerifyBoundCx<'cx, 'tcx>

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

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impl<'cx, 'tcx> !UnwindSafe for VerifyBoundCx<'cx, 'tcx>

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Size: 40 bytes