Adopt let_else in more places in rustc_mir_build

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 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;
-            } else {
-                break;
-            }
         }
         // at least the first candidate ought to be tested
         assert!(total_candidate_count > candidates.len());

compiler/rustc_mir_build/src/build/mod.rs

@@ -966,7 +966,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 DropKind::Value,
             );
 
-            if let Some(arg) = arg_opt {
+            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),
@@ -1012,14 +1014,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         Some((Some(&place), span)),
                     );
                     let place_builder = PlaceBuilder::from(local);
-                        unpack!(
-                            block = self.place_into_pattern(block, pattern, place_builder, false)
-                        );
+                    unpack!(block = self.place_into_pattern(block, pattern, place_builder, false));
                 }
             }
             self.source_scope = original_source_scope;
         }
-        }
 
         // Enter the argument pattern bindings source scope, if it exists.
         if let Some(source_scope) = scope {

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -256,7 +256,13 @@ 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() {
+                    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) {
@@ -267,13 +273,6 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                             self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
                         }
                     }
-                    } else {
-                        span_bug!(
-                            pat.span,
-                            "BindingMode::ByRef in pattern, but found non-reference type {}",
-                            ty
-                        );
-                    }
                 }
                 visit::walk_pat(self, pat);
             }