Use the correct span for simplifying or-patterns

We have to make sure we set it everywhere that we set `subcandidates`.

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -1006,6 +1006,10 @@ struct Candidate<'pat, 'tcx> {
  /// If the candidate matches, bindings and ascriptions must be established.
  extra_data: PatternExtraData<'tcx>,
 
+ /// If we filled `self.subcandidate`, we store here the span of the or-pattern they came from.
+ // Invariant: it is `None` iff `subcandidates.is_empty()`.
+ or_span: Option<Span>,
+
  /// The block before the `bindings` have been established.
  pre_binding_block: Option<BasicBlock>,
  /// The pre-binding block of the next candidate.
@@ -1028,6 +1032,7 @@ impl<'tcx, 'pat> Candidate<'pat, 'tcx> {
  extra_data: flat_pat.extra_data,
  has_guard,
  subcandidates: Vec::new(),
+ or_span: None,
  otherwise_block: None,
  pre_binding_block: None,
  next_candidate_pre_binding_block: None,
@@ -1277,7 +1282,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  //
  // only generates a single switch.
  candidate.subcandidates = self.create_or_subcandidates(pats, candidate.has_guard);
- candidate.match_pairs.pop();
+ let first_match_pair = candidate.match_pairs.pop().unwrap();
+ candidate.or_span = Some(first_match_pair.pattern.span);
  split_or_candidate = true;
  }
  }
@@ -1531,16 +1537,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  &mut or_candidate_refs,
  );
  candidate.subcandidates = or_candidates;
- self.merge_trivial_subcandidates(candidate, self.source_info(or_span));
+ candidate.or_span = Some(or_span);
+ self.merge_trivial_subcandidates(candidate);
  }
 
  /// Try to merge all of the subcandidates of the given candidate into one.
  /// This avoids exponentially large CFGs in cases like `(1 | 2, 3 | 4, ...)`.
- fn merge_trivial_subcandidates(
- &mut self,
- candidate: &mut Candidate<'_, 'tcx>,
- source_info: SourceInfo,
- ) {
+ fn merge_trivial_subcandidates(&mut self, candidate: &mut Candidate<'_, 'tcx>) {
  if candidate.subcandidates.is_empty() || candidate.has_guard {
  // FIXME(or_patterns; matthewjasper) Don't give up if we have a guard.
  return;
@@ -1550,7 +1553,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
  // Not `Iterator::all` because we don't want to short-circuit.
  for subcandidate in &mut candidate.subcandidates {
- self.merge_trivial_subcandidates(subcandidate, source_info);
+ self.merge_trivial_subcandidates(subcandidate);
 
  // FIXME(or_patterns; matthewjasper) Try to be more aggressive here.
  can_merge &=
@@ -1559,6 +1562,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
  if can_merge {
  let any_matches = self.cfg.start_new_block();
+ let or_span = candidate.or_span.take().unwrap();
+ let source_info = self.source_info(or_span);
  for subcandidate in mem::take(&mut candidate.subcandidates) {
  let or_block = subcandidate.pre_binding_block.unwrap();
  self.cfg.goto(or_block, source_info, any_matches);

compiler/rustc_mir_build/src/build/matches/simplify.rs

@@ -82,7 +82,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  &*candidate.match_pairs
  {
  candidate.subcandidates = self.create_or_subcandidates(pats, has_guard);
- candidate.match_pairs.pop();
+ let first_match_pair = candidate.match_pairs.pop().unwrap();
+ candidate.or_span = Some(first_match_pair.pattern.span);
  }
  candidate
  })