Struct rustc_mir_build::build::matches::Candidate

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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.

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§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:

Invariants:

§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§

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impl<'tcx, 'pat> Candidate<'pat, 'tcx>

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fn new( place: PlaceBuilder<'tcx>, pattern: &'pat Pat<'tcx>, has_guard: HasMatchGuard, cx: &mut Builder<'_, 'tcx>, ) -> Self

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fn from_flat_pat(flat_pat: FlatPat<'pat, 'tcx>, has_guard: bool) -> Self

Incorporates an already-simplified FlatPat into a new candidate.

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fn starts_with_or_pattern(&self) -> bool

Returns whether the first match pair of this candidate is an or-pattern.

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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.

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fn visit_leaves_rev<'a>(&'a mut self, visit_leaf: impl FnMut(&'a mut Self))

Visit the leaf candidates in reverse order.

Trait Implementations§

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impl<'pat, 'tcx> Debug for Candidate<'pat, 'tcx>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

Auto Trait Implementations§

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impl<'pat, 'tcx> Freeze for Candidate<'pat, 'tcx>

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impl<'pat, 'tcx> !RefUnwindSafe for Candidate<'pat, 'tcx>

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impl<'pat, 'tcx> !Send for Candidate<'pat, 'tcx>

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impl<'pat, 'tcx> !Sync for Candidate<'pat, 'tcx>

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impl<'pat, 'tcx> Unpin for Candidate<'pat, 'tcx>

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impl<'pat, 'tcx> !UnwindSafe for Candidate<'pat, 'tcx>

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Size: 144 bytes