Struct rustc::traits::project::ProjectionCache [−][src]
pub struct ProjectionCache<'tcx> { map: SnapshotMap<ProjectionCacheKey<'tcx>, ProjectionCacheEntry<'tcx>>, }
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The projection cache. Unlike the standard caches, this can include infcx-dependent type variables - therefore, we have to roll the cache back each time we roll a snapshot back, to avoid assumptions on yet-unresolved inference variables. Types with skolemized regions also have to be removed when the respective snapshot ends.
Because of that, projection cache entries can be "stranded" and left inaccessible when type variables inside the key are resolved. We make no attempt to recover or remove "stranded" entries, but rather let them be (for the lifetime of the infcx).
Entries in the projection cache might contain inference variables that will be resolved by obligations on the projection cache entry - e.g. when a type parameter in the associated type is constrained through an "RFC 447" projection on the impl.
When working with a fulfillment context, the derived obligations of each projection cache entry will be registered on the fulfillcx, so any users that can wait for a fulfillcx fixed point need not care about this. However, users that don't wait for a fixed point (e.g. trait evaluation) have to resolve the obligations themselves to make sure the projected result is ok and avoid issues like #43132.
If that is done, after evaluation the obligations, it is a good idea to
call ProjectionCache::complete
to make sure the obligations won't be
re-evaluated and avoid an exponential worst-case.
FIXME: we probably also want some sort of cross-infcx cache here to reduce the amount of duplication. Let's see what we get with the Chalk reforms.
Fields
map: SnapshotMap<ProjectionCacheKey<'tcx>, ProjectionCacheEntry<'tcx>>
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Methods
impl<'tcx> ProjectionCache<'tcx>
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impl<'tcx> ProjectionCache<'tcx>
pub fn new() -> Self
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pub fn new() -> Self
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pub fn clear(&mut self)
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pub fn clear(&mut self)
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pub fn snapshot(&mut self) -> ProjectionCacheSnapshot
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pub fn snapshot(&mut self) -> ProjectionCacheSnapshot
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pub fn rollback_to(&mut self, snapshot: ProjectionCacheSnapshot)
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pub fn rollback_to(&mut self, snapshot: ProjectionCacheSnapshot)
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pub fn rollback_skolemized(&mut self, snapshot: &ProjectionCacheSnapshot)
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pub fn rollback_skolemized(&mut self, snapshot: &ProjectionCacheSnapshot)
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pub fn commit(&mut self, snapshot: ProjectionCacheSnapshot)
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pub fn commit(&mut self, snapshot: ProjectionCacheSnapshot)
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fn try_start(
&mut self,
key: ProjectionCacheKey<'tcx>
) -> Result<(), ProjectionCacheEntry<'tcx>>
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fn try_start(
&mut self,
key: ProjectionCacheKey<'tcx>
) -> Result<(), ProjectionCacheEntry<'tcx>>
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Try to start normalize key
; returns an error if
normalization already occurred (this error corresponds to a
cache hit, so it's actually a good thing).
fn insert_ty(
&mut self,
key: ProjectionCacheKey<'tcx>,
value: Normalized<'tcx, Ty<'tcx>>
)
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fn insert_ty(
&mut self,
key: ProjectionCacheKey<'tcx>,
value: Normalized<'tcx, Ty<'tcx>>
)
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Indicates that key
was normalized to value
.
pub fn complete(&mut self, key: ProjectionCacheKey<'tcx>)
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pub fn complete(&mut self, key: ProjectionCacheKey<'tcx>)
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Mark the relevant projection cache key as having its derived obligations complete, so they won't have to be re-computed (this is OK to do in a snapshot - if the snapshot is rolled back, the obligations will be marked as incomplete again).
pub fn complete_normalized(
&mut self,
key: ProjectionCacheKey<'tcx>,
ty: &Normalized<'tcx, Ty<'tcx>>
)
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pub fn complete_normalized(
&mut self,
key: ProjectionCacheKey<'tcx>,
ty: &Normalized<'tcx, Ty<'tcx>>
)
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A specialized version of complete
for when the key's value is known
to be a NormalizedTy.
fn ambiguous(&mut self, key: ProjectionCacheKey<'tcx>)
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fn ambiguous(&mut self, key: ProjectionCacheKey<'tcx>)
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Indicates that trying to normalize key
resulted in
ambiguity. No point in trying it again then until we gain more
type information (in which case, the "fully resolved" key will
be different).
fn error(&mut self, key: ProjectionCacheKey<'tcx>)
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fn error(&mut self, key: ProjectionCacheKey<'tcx>)
🔬 This is a nightly-only experimental API. (rustc_private
)
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Indicates that trying to normalize key
resulted in
error.
Auto Trait Implementations
impl<'tcx> !Send for ProjectionCache<'tcx>
impl<'tcx> !Send for ProjectionCache<'tcx>
impl<'tcx> !Sync for ProjectionCache<'tcx>
impl<'tcx> !Sync for ProjectionCache<'tcx>