Struct rustc_infer::infer::outlives::verify::VerifyBoundCx
source · pub struct VerifyBoundCx<'cx, 'tcx> {
tcx: TyCtxt<'tcx>,
region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
implicit_region_bound: Option<Region<'tcx>>,
param_env: ParamEnv<'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.
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§
source§impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx>
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 param_bound(&self, param_ty: ParamTy) -> VerifyBound<'tcx>
sourcepub fn approx_declared_bounds_from_env(
&self,
alias_ty: AliasTy<'tcx>
) -> Vec<Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>
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.
pub fn alias_bound( &self, alias_ty: AliasTy<'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>
sourcefn declared_generic_bounds_from_env(
&self,
param_ty: ParamTy
) -> Vec<Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'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.
sourcefn declared_generic_bounds_from_env_for_erased_ty(
&self,
erased_ty: Ty<'tcx>
) -> Vec<Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>
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.
sourcepub fn declared_bounds_from_definition(
&self,
alias_ty: AliasTy<'tcx>
) -> impl Iterator<Item = Region<'tcx>>
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 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:
```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.
sourcefn collect_outlives_from_clause_list(
&self,
erased_ty: Ty<'tcx>,
clauses: impl Iterator<Item = Clause<'tcx>>
) -> impl Iterator<Item = Binder<'tcx, OutlivesPredicate<Ty<'tcx>, Region<'tcx>>>>
fn collect_outlives_from_clause_list( &self, erased_ty: Ty<'tcx>, clauses: impl Iterator<Item = Clause<'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.
Auto Trait Implementations§
impl<'cx, 'tcx> !RefUnwindSafe for VerifyBoundCx<'cx, 'tcx>
impl<'cx, 'tcx> !Send for VerifyBoundCx<'cx, 'tcx>
impl<'cx, 'tcx> !Sync for VerifyBoundCx<'cx, 'tcx>
impl<'cx, 'tcx> Unpin for VerifyBoundCx<'cx, 'tcx>
impl<'cx, 'tcx> !UnwindSafe for VerifyBoundCx<'cx, 'tcx>
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
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