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§
source§impl<'tcx> RegionConstraintCollector<'_, 'tcx>
impl<'tcx> RegionConstraintCollector<'_, 'tcx>
sourcepub fn leak_check(
&mut self,
tcx: TyCtxt<'tcx>,
outer_universe: UniverseIndex,
max_universe: UniverseIndex,
only_consider_snapshot: Option<&CombinedSnapshot<'tcx>>,
) -> Result<(), TypeError<TyCtxt<'tcx>>>
pub fn leak_check( &mut self, tcx: TyCtxt<'tcx>, outer_universe: UniverseIndex, max_universe: UniverseIndex, only_consider_snapshot: Option<&CombinedSnapshot<'tcx>>, ) -> Result<(), TypeError<TyCtxt<'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). This algorithm
only looks at placeholders which cannot be named by outer_universe
,
as this is the universe we’re currently checking for a leak.
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
To improve performance and for the old trait solver caching to be sound, this takes
an optional snapshot in which case we only look at region constraints added in that
snapshot. If we were to not do that the leak_check
during evaluation can rely on
region constraints added outside of that evaluation. As that is not reflected in the
cache key this would be unsound.
§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
source§impl<'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,
) -> (IndexVec<RegionVid, RegionVariableInfo>, RegionConstraintData<'tcx>)
pub fn into_infos_and_data( self, ) -> (IndexVec<RegionVid, RegionVariableInfo>, 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 fn data(&self) -> &RegionConstraintData<'tcx>
sourcepub fn opportunistic_resolve_var(
&mut self,
tcx: TyCtxt<'tcx>,
vid: RegionVid,
) -> Region<'tcx>
pub fn opportunistic_resolve_var( &mut self, tcx: TyCtxt<'tcx>, vid: RegionVid, ) -> Region<'tcx>
Resolves a region var to its value in the unification table, if it exists.
Otherwise, it is resolved to the root ReVar
in the table.
pub fn probe_value( &mut self, vid: RegionVid, ) -> Result<Region<'tcx>, UniverseIndex>
pub fn universe(&mut 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>,
) -> bool
pub fn region_constraints_added_in_snapshot( &self, mark: &Snapshot<'tcx>, ) -> bool
See InferCtxt::region_constraints_added_in_snapshot
.
Trait Implementations§
source§impl<'tcx> Deref for RegionConstraintCollector<'_, 'tcx>
impl<'tcx> Deref for RegionConstraintCollector<'_, 'tcx>
§type Target = RegionConstraintStorage<'tcx>
type Target = RegionConstraintStorage<'tcx>
source§fn deref(&self) -> &RegionConstraintStorage<'tcx>
fn deref(&self) -> &RegionConstraintStorage<'tcx>
source§impl<'tcx> DerefMut for RegionConstraintCollector<'_, 'tcx>
impl<'tcx> DerefMut for RegionConstraintCollector<'_, 'tcx>
source§fn deref_mut(&mut self) -> &mut RegionConstraintStorage<'tcx>
fn deref_mut(&mut self) -> &mut RegionConstraintStorage<'tcx>
Auto Trait Implementations§
impl<'a, 'tcx> Freeze for RegionConstraintCollector<'a, 'tcx>
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>
impl<'a, 'tcx> !UnwindSafe for RegionConstraintCollector<'a, 'tcx>
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Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...)
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Size: 16 bytes