Struct rustc_mir_build::build::matches::Candidate
source · struct Candidate<'pat, 'tcx> {
match_pairs: Vec<MatchPairTree<'pat, 'tcx>>,
subcandidates: Vec<Candidate<'pat, 'tcx>>,
has_guard: bool,
extra_data: PatternExtraData<'tcx>,
or_span: Option<Span>,
pre_binding_block: Option<BasicBlock>,
otherwise_block: Option<BasicBlock>,
false_edge_start_block: Option<BasicBlock>,
}
Expand description
Candidates are a generalization of (a) top-level match arms, and
(b) sub-branches of or-patterns, allowing the match-lowering process to handle
them both in a mostly-uniform way. For example, the list of candidates passed
to Builder::match_candidates
will often contain a mixture of top-level
candidates and or-pattern subcandidates.
At the start of match lowering, there is one candidate for each match arm. During match lowering, arms with or-patterns will be expanded into a tree of candidates, where each “leaf” candidate represents one of the ways for the arm pattern to successfully match.
Fields§
§match_pairs: Vec<MatchPairTree<'pat, 'tcx>>
For the candidate to match, all of these must be satisfied…
Initially contains a list of match pairs created by FlatPat
, but is
subsequently mutated (in a queue-like way) while lowering the match tree.
When this list becomes empty, the candidate is fully matched and becomes
a leaf (see Builder::select_matched_candidate
).
Key mutations include:
- When a match pair is fully satisfied by a test, it is removed from the
list, and its subpairs are added instead (see
Builder::sort_candidate
). - During or-pattern expansion, any leading or-pattern is removed, and is
converted into subcandidates (see
Builder::expand_and_match_or_candidates
). - After a candidate’s subcandidates have been lowered, a copy of any remaining
or-patterns is added to each leaf subcandidate
(see
Builder::test_remaining_match_pairs_after_or
).
Invariants:
- All
TestCase::Irrefutable
patterns have been removed by simplification. - All or-patterns (
TestCase::Or
) have been sorted to the end.
subcandidates: Vec<Candidate<'pat, 'tcx>>
…and if this is non-empty, one of these subcandidates also has to match…
Initially a candidate has no subcandidates; they are added (and then immediately lowered) during or-pattern expansion. Their main function is to serve as output of match tree lowering, allowing later steps to see the leaf candidates that represent a match of the entire match arm.
A candidate no subcandidates is either incomplete (if it has match pairs left), or is a leaf in the match tree. A candidate with one or more subcandidates is an internal node in the match tree.
Invariant: at the end of match tree lowering, this must not contain an
is_never
candidate, because that would break binding consistency.
has_guard: bool
…and if there is a guard it must be evaluated; if it’s false
then branch to otherwise_block
.
For subcandidates, this is copied from the parent candidate, so it indicates whether the enclosing match arm has a guard.
extra_data: PatternExtraData<'tcx>
Holds extra pattern data that was prepared by FlatPat
, including bindings and
ascriptions that must be established if this candidate succeeds.
or_span: Option<Span>
When setting self.subcandidates
, we store here the span of the or-pattern they came from.
Invariant: it is None
iff subcandidates.is_empty()
.
- FIXME: We sometimes don’t unset this when clearing
subcandidates
.
pre_binding_block: Option<BasicBlock>
The block before the bindings
have been established.
After the match tree has been lowered, Builder::lower_match_arms
will use this as the start point for lowering bindings and guards, and
then jump to a shared block containing the arm body.
otherwise_block: Option<BasicBlock>
The block to branch to if the guard or a nested candidate fails to match.
false_edge_start_block: Option<BasicBlock>
The earliest block that has only candidates >= this one as descendents. Used for false
edges, see the doc for Builder::match_expr
.
Implementations§
source§impl<'tcx, 'pat> Candidate<'pat, 'tcx>
impl<'tcx, 'pat> Candidate<'pat, 'tcx>
fn new( place: PlaceBuilder<'tcx>, pattern: &'pat Pat<'tcx>, has_guard: HasMatchGuard, cx: &mut Builder<'_, 'tcx>, ) -> Self
sourcefn from_flat_pat(flat_pat: FlatPat<'pat, 'tcx>, has_guard: bool) -> Self
fn from_flat_pat(flat_pat: FlatPat<'pat, 'tcx>, has_guard: bool) -> Self
Incorporates an already-simplified FlatPat
into a new candidate.
sourcefn starts_with_or_pattern(&self) -> bool
fn starts_with_or_pattern(&self) -> bool
Returns whether the first match pair of this candidate is an or-pattern.
sourcefn visit_leaves<'a>(&'a mut self, visit_leaf: impl FnMut(&'a mut Self))
fn visit_leaves<'a>(&'a mut self, visit_leaf: impl FnMut(&'a mut Self))
Visit the leaf candidates (those with no subcandidates) contained in this candidate.
sourcefn visit_leaves_rev<'a>(&'a mut self, visit_leaf: impl FnMut(&'a mut Self))
fn visit_leaves_rev<'a>(&'a mut self, visit_leaf: impl FnMut(&'a mut Self))
Visit the leaf candidates in reverse order.
Trait Implementations§
Auto Trait Implementations§
impl<'pat, 'tcx> Freeze for Candidate<'pat, 'tcx>
impl<'pat, 'tcx> !RefUnwindSafe for Candidate<'pat, 'tcx>
impl<'pat, 'tcx> !Send for Candidate<'pat, 'tcx>
impl<'pat, 'tcx> !Sync for Candidate<'pat, 'tcx>
impl<'pat, 'tcx> Unpin for Candidate<'pat, 'tcx>
impl<'pat, 'tcx> !UnwindSafe for Candidate<'pat, '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
source§impl<T, R> CollectAndApply<T, R> for T
impl<T, R> CollectAndApply<T, R> for T
source§impl<T> Filterable for T
impl<T> Filterable for T
source§fn filterable(
self,
filter_name: &'static str,
) -> RequestFilterDataProvider<T, fn(_: DataRequest<'_>) -> bool>
fn filterable( self, filter_name: &'static str, ) -> RequestFilterDataProvider<T, fn(_: DataRequest<'_>) -> bool>
source§impl<T> Instrument for T
impl<T> Instrument for T
source§fn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
source§fn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
source§impl<T> IntoEither for T
impl<T> IntoEither for T
source§fn into_either(self, into_left: bool) -> Either<Self, Self>
fn into_either(self, into_left: bool) -> Either<Self, Self>
self
into a Left
variant of Either<Self, Self>
if into_left
is true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read moresource§fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
self
into a Left
variant of Either<Self, Self>
if into_left(&self)
returns true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read moresource§impl<P> IntoQueryParam<P> for P
impl<P> IntoQueryParam<P> for P
fn into_query_param(self) -> P
source§impl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
source§impl<I, T, U> Upcast<I, U> for Twhere
U: UpcastFrom<I, T>,
impl<I, T, U> Upcast<I, U> for Twhere
U: UpcastFrom<I, T>,
source§impl<I, T> UpcastFrom<I, T> for T
impl<I, T> UpcastFrom<I, T> for T
fn upcast_from(from: T, _tcx: I) -> T
source§impl<Tcx, T> Value<Tcx> for Twhere
Tcx: DepContext,
impl<Tcx, T> Value<Tcx> for Twhere
Tcx: DepContext,
default fn from_cycle_error( tcx: Tcx, cycle_error: &CycleError, _guar: ErrorGuaranteed, ) -> T
source§impl<T> WithSubscriber for T
impl<T> WithSubscriber for T
source§fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
source§fn with_current_subscriber(self) -> WithDispatch<Self>
fn with_current_subscriber(self) -> WithDispatch<Self>
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
impl<T> ErasedDestructor for Twhere
T: 'static,
impl<T> MaybeSendSync for 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: 144 bytes