Use more let_else in rustc_mir_build

Helps avoid rightward drift.

Author: est31

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

@@ -1606,13 +1606,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // encounter a candidate where the test is not relevant; at
         // that point, we stop sorting.
         while let Some(candidate) = candidates.first_mut() {
-            if let Some(idx) = self.sort_candidate(&match_place.clone(), &test, candidate) {
-                let (candidate, rest) = candidates.split_first_mut().unwrap();
-                target_candidates[idx].push(candidate);
-                candidates = rest;
-            } else {
+            let Some(idx) = self.sort_candidate(&match_place.clone(), &test, candidate) else {
                 break;
-            }
+            };
+            let (candidate, rest) = candidates.split_first_mut().unwrap();
+            target_candidates[idx].push(candidate);
+            candidates = rest;
         }
         // at least the first candidate ought to be tested
         assert!(total_candidate_count > candidates.len());

compiler/rustc_mir_build/src/build/mod.rs

@@ -966,59 +966,58 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 DropKind::Value,
             );
 
-            if let Some(arg) = arg_opt {
-                let pat = match tcx.hir().get(arg.pat.hir_id) {
-                    Node::Pat(pat) | Node::Binding(pat) => pat,
-                    node => bug!("pattern became {:?}", node),
-                };
-                let pattern = pat_from_hir(tcx, self.param_env, self.typeck_results, pat);
-                let original_source_scope = self.source_scope;
-                let span = pattern.span;
-                self.set_correct_source_scope_for_arg(arg.hir_id, original_source_scope, span);
-                match *pattern.kind {
-                    // Don't introduce extra copies for simple bindings
-                    PatKind::Binding {
-                        mutability,
-                        var,
-                        mode: BindingMode::ByValue,
-                        subpattern: None,
-                        ..
-                    } => {
-                        self.local_decls[local].mutability = mutability;
-                        self.local_decls[local].source_info.scope = self.source_scope;
-                        self.local_decls[local].local_info = if let Some(kind) = self_binding {
-                            Some(Box::new(LocalInfo::User(ClearCrossCrate::Set(
-                                BindingForm::ImplicitSelf(*kind),
-                            ))))
-                        } else {
-                            let binding_mode = ty::BindingMode::BindByValue(mutability);
-                            Some(Box::new(LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
-                                VarBindingForm {
-                                    binding_mode,
-                                    opt_ty_info,
-                                    opt_match_place: Some((Some(place), span)),
-                                    pat_span: span,
-                                },
-                            )))))
-                        };
-                        self.var_indices.insert(var, LocalsForNode::One(local));
-                    }
-                    _ => {
-                        scope = self.declare_bindings(
-                            scope,
-                            expr.span,
-                            &pattern,
-                            matches::ArmHasGuard(false),
-                            Some((Some(&place), span)),
-                        );
-                        let place_builder = PlaceBuilder::from(local);
-                        unpack!(
-                            block = self.place_into_pattern(block, pattern, place_builder, false)
-                        );
-                    }
+            let Some(arg) = arg_opt else {
+                continue;
+            };
+            let pat = match tcx.hir().get(arg.pat.hir_id) {
+                Node::Pat(pat) | Node::Binding(pat) => pat,
+                node => bug!("pattern became {:?}", node),
+            };
+            let pattern = pat_from_hir(tcx, self.param_env, self.typeck_results, pat);
+            let original_source_scope = self.source_scope;
+            let span = pattern.span;
+            self.set_correct_source_scope_for_arg(arg.hir_id, original_source_scope, span);
+            match *pattern.kind {
+                // Don't introduce extra copies for simple bindings
+                PatKind::Binding {
+                    mutability,
+                    var,
+                    mode: BindingMode::ByValue,
+                    subpattern: None,
+                    ..
+                } => {
+                    self.local_decls[local].mutability = mutability;
+                    self.local_decls[local].source_info.scope = self.source_scope;
+                    self.local_decls[local].local_info = if let Some(kind) = self_binding {
+                        Some(Box::new(LocalInfo::User(ClearCrossCrate::Set(
+                            BindingForm::ImplicitSelf(*kind),
+                        ))))
+                    } else {
+                        let binding_mode = ty::BindingMode::BindByValue(mutability);
+                        Some(Box::new(LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
+                            VarBindingForm {
+                                binding_mode,
+                                opt_ty_info,
+                                opt_match_place: Some((Some(place), span)),
+                                pat_span: span,
+                            },
+                        )))))
+                    };
+                    self.var_indices.insert(var, LocalsForNode::One(local));
+                }
+                _ => {
+                    scope = self.declare_bindings(
+                        scope,
+                        expr.span,
+                        &pattern,
+                        matches::ArmHasGuard(false),
+                        Some((Some(&place), span)),
+                    );
+                    let place_builder = PlaceBuilder::from(local);
+                    unpack!(block = self.place_into_pattern(block, pattern, place_builder, false));
                 }
-                self.source_scope = original_source_scope;
             }
+            self.source_scope = original_source_scope;
         }
 
         // Enter the argument pattern bindings source scope, if it exists.

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -256,23 +256,22 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
             }
             PatKind::Binding { mode: BindingMode::ByRef(borrow_kind), ty, .. } => {
                 if self.inside_adt {
-                    if let ty::Ref(_, ty, _) = ty.kind() {
-                        match borrow_kind {
-                            BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {
-                                if !ty.is_freeze(self.tcx.at(pat.span), self.param_env) {
-                                    self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
-                                }
-                            }
-                            BorrowKind::Mut { .. } => {
-                                self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
-                            }
-                        }
-                    } else {
+                    let ty::Ref(_, ty, _) = ty.kind() else {
                         span_bug!(
                             pat.span,
                             "BindingMode::ByRef in pattern, but found non-reference type {}",
                             ty
                         );
+                    };
+                    match borrow_kind {
+                        BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {
+                            if !ty.is_freeze(self.tcx.at(pat.span), self.param_env) {
+                                self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
+                            }
+                        }
+                        BorrowKind::Mut { .. } => {
+                            self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
+                        }
                     }
                 }
                 visit::walk_pat(self, pat);