reverse binding order in matches to allow the subbinding of copyable fields in bindings after @

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

@@ -44,6 +44,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  candidate: &mut Candidate<'pat, 'tcx>,
  ) -> bool {
  // repeatedly simplify match pairs until fixed point is reached
+ debug!("simplify_candidate(candidate={:?})", candidate);
+ let mut new_bindings = Vec::new();
  loop {
  let match_pairs = mem::take(&mut candidate.match_pairs);
 
@@ -56,7 +58,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
  let mut changed = false;
  for match_pair in match_pairs {
- match self.simplify_match_pair(match_pair, candidate) {
+ match self.simplify_match_pair(match_pair, candidate, &mut new_bindings) {
  Ok(()) => {
  changed = true;
  }
@@ -65,13 +67,31 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  }
  }
  }
+ // issue #69971: the binding order should be right to left if there are more
+ // bindings after `@` to please the borrow checker
+ // Ex
+ // struct NonCopyStruct {
+ // copy_field: u32,
+ // }
+ //
+ // fn foo1(x: NonCopyStruct) {
+ // let y @ NonCopyStruct { copy_field: z } = x;
+ // // the above should turn into
+ // let z = x.copy_field;
+ // let y = x;
+ // }
+ new_bindings.extend_from_slice(&candidate.bindings);
+ mem::swap(&mut candidate.bindings, &mut new_bindings);
+ new_bindings.clear();
+
  if !changed {
  // Move or-patterns to the end, because they can result in us
  // creating additional candidates, so we want to test them as
  // late as possible.
  candidate
  .match_pairs
  .sort_by_key(|pair| matches!(*pair.pattern.kind, PatKind::Or { .. }));
+ debug!("simplify_candidate: simplifed {:?}", candidate);
  return false; // if we were not able to simplify any, done.
  }
  }
@@ -104,6 +124,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  &mut self,
  match_pair: MatchPair<'pat, 'tcx>,
  candidate: &mut Candidate<'pat, 'tcx>,
+ bindings: &mut Vec<Binding<'tcx>>,
  ) -> Result<(), MatchPair<'pat, 'tcx>> {
  let tcx = self.hir.tcx();
  match *match_pair.pattern.kind {
@@ -131,7 +152,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  }
 
  PatKind::Binding { name, mutability, mode, var, ty, ref subpattern, is_primary: _ } => {
- candidate.bindings.push(Binding {
+ bindings.push(Binding {
  name,
  mutability,
  span: match_pair.pattern.span,

src/test/mir-opt/early_otherwise_branch.opt1.EarlyOtherwiseBranch.diff

@@ -52,13 +52,13 @@
 - }
 - 
 - bb3: {
- StorageLive(_8); // scope 0 at $DIR/early_otherwise_branch.rs:5:15: 5:16
- _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:5:15: 5:16
  StorageLive(_9); // scope 0 at $DIR/early_otherwise_branch.rs:5:24: 5:25
  _9 = (((_3.1: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:5:24: 5:25
+ StorageLive(_8); // scope 0 at $DIR/early_otherwise_branch.rs:5:15: 5:16
+ _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:5:15: 5:16
  _0 = const 0_u32; // scope 1 at $DIR/early_otherwise_branch.rs:5:31: 5:32
- StorageDead(_9); // scope 0 at $DIR/early_otherwise_branch.rs:5:31: 5:32
  StorageDead(_8); // scope 0 at $DIR/early_otherwise_branch.rs:5:31: 5:32
+ StorageDead(_9); // scope 0 at $DIR/early_otherwise_branch.rs:5:31: 5:32
 - goto -> bb4; // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 7:6
 + goto -> bb3; // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 7:6
  }

src/test/mir-opt/early_otherwise_branch.opt2.EarlyOtherwiseBranch.diff

@@ -59,13 +59,13 @@
 - 
 - bb4: {
 + bb2: {
- StorageLive(_9); // scope 0 at $DIR/early_otherwise_branch.rs:13:15: 13:16
- _9 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:13:15: 13:16
  StorageLive(_10); // scope 0 at $DIR/early_otherwise_branch.rs:13:24: 13:25
  _10 = (((_3.1: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:13:24: 13:25
+ StorageLive(_9); // scope 0 at $DIR/early_otherwise_branch.rs:13:15: 13:16
+ _9 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:13:15: 13:16
  _0 = const 0_u32; // scope 1 at $DIR/early_otherwise_branch.rs:13:31: 13:32
- StorageDead(_10); // scope 0 at $DIR/early_otherwise_branch.rs:13:31: 13:32
  StorageDead(_9); // scope 0 at $DIR/early_otherwise_branch.rs:13:31: 13:32
+ StorageDead(_10); // scope 0 at $DIR/early_otherwise_branch.rs:13:31: 13:32
 - goto -> bb6; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 16:6
 + goto -> bb4; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 16:6
  }

src/test/mir-opt/early_otherwise_branch_3_element_tuple.opt1.EarlyOtherwiseBranch.diff

@@ -71,16 +71,16 @@
 
 - bb4: {
 + bb3: {
- StorageLive(_11); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:15: 6:16
- _11 = (((_4.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:15: 6:16
- StorageLive(_12); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:24: 6:25
- _12 = (((_4.1: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:24: 6:25
  StorageLive(_13); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:33: 6:34
  _13 = (((_4.2: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:33: 6:34
+ StorageLive(_12); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:24: 6:25
+ _12 = (((_4.1: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:24: 6:25
+ StorageLive(_11); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:15: 6:16
+ _11 = (((_4.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:15: 6:16
  _0 = const 0_u32; // scope 1 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:40: 6:41
- StorageDead(_13); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:40: 6:41
- StorageDead(_12); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:40: 6:41
  StorageDead(_11); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:40: 6:41
+ StorageDead(_12); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:40: 6:41
+ StorageDead(_13); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:40: 6:41
 - goto -> bb5; // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 8:6
 + goto -> bb4; // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 8:6
  }