pub struct RegionConstraintCollector<'a, 'tcx> {
storage: &'a mut RegionConstraintStorage<'tcx>,
undo_log: &'a mut InferCtxtUndoLogs<'tcx>,
}
Fields
storage: &'a mut RegionConstraintStorage<'tcx>
undo_log: &'a mut InferCtxtUndoLogs<'tcx>
Implementations
sourceimpl<'tcx> RegionConstraintCollector<'_, 'tcx>
impl<'tcx> RegionConstraintCollector<'_, 'tcx>
sourcepub fn leak_check(
&mut self,
tcx: TyCtxt<'tcx>,
overly_polymorphic: bool,
max_universe: UniverseIndex,
snapshot: &CombinedSnapshot<'_, 'tcx>
) -> RelateResult<'tcx, ()>
pub fn leak_check(
&mut self,
tcx: TyCtxt<'tcx>,
overly_polymorphic: bool,
max_universe: UniverseIndex,
snapshot: &CombinedSnapshot<'_, 'tcx>
) -> RelateResult<'tcx, ()>
Searches new universes created during snapshot
, looking for
placeholders that may “leak” out from the universes they are contained
in. If any leaking placeholders are found, then an Err
is returned
(typically leading to the snapshot being reversed).
The leak check used to be the only way we had to handle higher-ranked obligations. Now that we have integrated universes into the region solvers, this is no longer the case, but we retain the leak check for backwards compatibility purposes. In particular, it lets us make “early” decisions about whether a region error will be reported that are used in coherence and elsewhere – see #56105 and #59490 for more details. The eventual fate of the leak checker is not yet settled.
The leak checker works by searching for the following error patterns:
- P1: P2, where P1 != P2
- P1: R, where R is in some universe that cannot name P1
The idea here is that each of these patterns represents something that
the region solver would eventually report as an error, so we can detect
the error early. There is a fly in the ointment, though, in that this is
not entirely true. In particular, in the future, we may extend the
environment with implied bounds or other info about how placeholders
relate to regions in outer universes. In that case, P1: R
for example
might become solvable.
Summary of the implementation
The leak checks as follows. First, we construct a graph where R2: R1
implies R2 -> R1
, and we compute the SCCs.
For each SCC S, we compute:
- what placeholder P it must be equal to, if any
- if there are multiple placeholders that must be equal, report an error because
P1: P2
- if there are multiple placeholders that must be equal, report an error because
- the minimum universe of its constituents
Then we walk the SCCs in dependency order and compute
- what placeholder they must outlive transitively
- if they must also be equal to a placeholder, report an error because
P1: P2
- if they must also be equal to a placeholder, report an error because
- minimum universe U of all SCCs they must outlive
- if they must also be equal to a placeholder P, and U cannot name P, report an error, as that
indicates
P: R
andR
is in an incompatible universe
- if they must also be equal to a placeholder P, and U cannot name P, report an error, as that
indicates
Historical note
Older variants of the leak check used to report errors for these patterns, but we no longer do:
- R: P1, even if R cannot name P1, because R = ’static is a valid sol’n
- R: P1, R: P2, as above
sourceimpl<'tcx> RegionConstraintCollector<'_, 'tcx>
impl<'tcx> RegionConstraintCollector<'_, 'tcx>
pub fn num_region_vars(&self) -> usize
pub fn region_constraint_data(&self) -> &RegionConstraintData<'tcx>
sourcepub fn into_infos_and_data(self) -> (VarInfos, RegionConstraintData<'tcx>)
pub fn into_infos_and_data(self) -> (VarInfos, RegionConstraintData<'tcx>)
Once all the constraints have been gathered, extract out the final data.
Not legal during a snapshot.
sourcepub fn take_and_reset_data(&mut self) -> RegionConstraintData<'tcx>
pub fn take_and_reset_data(&mut self) -> RegionConstraintData<'tcx>
Takes (and clears) the current set of constraints. Note that the set of variables remains intact, but all relationships between them are reset. This is used during NLL checking to grab the set of constraints that arose from a particular operation.
We don’t want to leak relationships between variables between
points because just because (say) r1 == r2
was true at some
point P in the graph doesn’t imply that it will be true at
some other point Q, in NLL.
Not legal during a snapshot.
pub(super) fn data(&self) -> &RegionConstraintData<'tcx>
pub(super) fn start_snapshot(&mut self) -> RegionSnapshot
pub(super) fn rollback_to(&mut self, snapshot: RegionSnapshot)
pub(super) fn new_region_var(
&mut self,
universe: UniverseIndex,
origin: RegionVariableOrigin
) -> RegionVid
sourcepub(super) fn var_universe(&self, vid: RegionVid) -> UniverseIndex
pub(super) fn var_universe(&self, vid: RegionVid) -> UniverseIndex
Returns the universe for the given variable.
sourcepub(super) fn var_origin(&self, vid: RegionVid) -> RegionVariableOrigin
pub(super) fn var_origin(&self, vid: RegionVid) -> RegionVariableOrigin
Returns the origin for the given variable.
fn add_constraint(
&mut self,
constraint: Constraint<'tcx>,
origin: SubregionOrigin<'tcx>
)
fn add_verify(&mut self, verify: Verify<'tcx>)
pub(super) fn add_given(&mut self, sub: Region<'tcx>, sup: RegionVid)
pub(super) fn make_eqregion(
&mut self,
origin: SubregionOrigin<'tcx>,
sub: Region<'tcx>,
sup: Region<'tcx>
)
pub(super) fn member_constraint(
&mut self,
key: OpaqueTypeKey<'tcx>,
definition_span: Span,
hidden_ty: Ty<'tcx>,
member_region: Region<'tcx>,
choice_regions: &Lrc<Vec<Region<'tcx>>>
)
pub(super) fn make_subregion(
&mut self,
origin: SubregionOrigin<'tcx>,
sub: Region<'tcx>,
sup: Region<'tcx>
)
pub(super) fn verify_generic_bound(
&mut self,
origin: SubregionOrigin<'tcx>,
kind: GenericKind<'tcx>,
sub: Region<'tcx>,
bound: VerifyBound<'tcx>
)
pub(super) fn lub_regions(
&mut self,
tcx: TyCtxt<'tcx>,
origin: SubregionOrigin<'tcx>,
a: Region<'tcx>,
b: Region<'tcx>
) -> Region<'tcx>
pub(super) fn glb_regions(
&mut self,
tcx: TyCtxt<'tcx>,
origin: SubregionOrigin<'tcx>,
a: Region<'tcx>,
b: Region<'tcx>
) -> Region<'tcx>
sourcepub(super) fn opportunistic_resolve_var(&mut self, rid: RegionVid) -> RegionVid
pub(super) fn opportunistic_resolve_var(&mut self, rid: RegionVid) -> RegionVid
Resolves the passed RegionVid to the root RegionVid in the unification table
sourcepub fn opportunistic_resolve_region(
&mut self,
tcx: TyCtxt<'tcx>,
region: Region<'tcx>
) -> Region<'tcx>
pub fn opportunistic_resolve_region(
&mut self,
tcx: TyCtxt<'tcx>,
region: Region<'tcx>
) -> Region<'tcx>
If the Region is a ReVar
, then resolves it either to the root value in
the unification table, if it exists, or to the root ReVar
in the table.
If the Region is not a ReVar
, just returns the Region itself.
fn combine_map(
&mut self,
t: CombineMapType
) -> &mut FxHashMap<TwoRegions<'tcx>, RegionVid>
fn combine_vars(
&mut self,
tcx: TyCtxt<'tcx>,
t: CombineMapType,
a: Region<'tcx>,
b: Region<'tcx>,
origin: SubregionOrigin<'tcx>
) -> Region<'tcx>
pub fn universe(&self, region: Region<'tcx>) -> UniverseIndex
pub fn vars_since_snapshot(
&self,
value_count: usize
) -> (Range<RegionVid>, Vec<RegionVariableOrigin>)
sourcepub fn region_constraints_added_in_snapshot(
&self,
mark: &Snapshot<'tcx>
) -> Option<bool>
pub fn region_constraints_added_in_snapshot(
&self,
mark: &Snapshot<'tcx>
) -> Option<bool>
See InferCtxt::region_constraints_added_in_snapshot
.
fn unification_table(
&mut self
) -> UnificationTable<InPlace<RegionVidKey<'tcx>, &'_ mut UnificationStorage<RegionVidKey<'tcx>>, &'_ mut InferCtxtUndoLogs<'tcx>>>
Methods from Deref<Target = RegionConstraintStorage<'tcx>>
pub(crate) fn with_log<'a>(
&'a mut self,
undo_log: &'a mut InferCtxtUndoLogs<'tcx>
) -> RegionConstraintCollector<'a, 'tcx>
fn rollback_undo_entry(&mut self, undo_entry: UndoLog<'tcx>)
Trait Implementations
sourceimpl<'tcx> Deref for RegionConstraintCollector<'_, 'tcx>
impl<'tcx> Deref for RegionConstraintCollector<'_, 'tcx>
type Target = RegionConstraintStorage<'tcx>
type Target = RegionConstraintStorage<'tcx>
sourcefn deref(&self) -> &RegionConstraintStorage<'tcx>
fn deref(&self) -> &RegionConstraintStorage<'tcx>
sourceimpl<'tcx> DerefMut for RegionConstraintCollector<'_, 'tcx>
impl<'tcx> DerefMut for RegionConstraintCollector<'_, 'tcx>
sourcefn deref_mut(&mut self) -> &mut RegionConstraintStorage<'tcx>
fn deref_mut(&mut self) -> &mut RegionConstraintStorage<'tcx>
Auto Trait Implementations
impl<'a, 'tcx> !RefUnwindSafe for RegionConstraintCollector<'a, 'tcx>
impl<'a, 'tcx> !Send for RegionConstraintCollector<'a, 'tcx>
impl<'a, 'tcx> !Sync for RegionConstraintCollector<'a, 'tcx>
impl<'a, 'tcx> Unpin for RegionConstraintCollector<'a, 'tcx>where
'tcx: 'a,
impl<'a, 'tcx> !UnwindSafe for RegionConstraintCollector<'a, 'tcx>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
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: 16 bytes