nll: improve common patterns

src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs

@@ -439,17 +439,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                             Operand::Move(Place::Local(from)) if *from == target => {
                                 debug!("was_captured_by_trait_object: ty={:?}", ty);
                                 // Check the type for a trait object.
-                                match ty.sty {
+                                return match ty.sty {
                                     // `&dyn Trait`
-                                    ty::TyKind::Ref(_, ty, _) if ty.is_trait() => return true,
+                                    ty::TyKind::Ref(_, ty, _) if ty.is_trait() => true,
                                     // `Box<dyn Trait>`
                                     _ if ty.is_box() && ty.boxed_ty().is_trait() =>
-                                        return true,
+                                        true,
                                     // `dyn Trait`
-                                    _ if ty.is_trait() => return true,
+                                    _ if ty.is_trait() => true,
                                     // Anything else.
-                                    _ => return false,
-                                }
+                                    _ => false,
+                                };
                             },
                             _ => return false,
                         },
@@ -464,12 +464,11 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 let terminator = block.terminator();
                 debug!("was_captured_by_trait_object: terminator={:?}", terminator);
 
-                match &terminator.kind {
-                    TerminatorKind::Call {
+                if let TerminatorKind::Call {
                     destination: Some((Place::Local(dest), block)),
                     args,
                     ..
-                    } => {
+                } = &terminator.kind {
                     debug!(
                         "was_captured_by_trait_object: target={:?} dest={:?} args={:?}",
                         target, dest, args
@@ -488,8 +487,6 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                         target = *dest;
                         queue.push(block.start_location());
                     }
-                    },
-                    _ => {},
                 }
             }
 

src/librustc_mir/borrow_check/nll/invalidation.rs

@@ -35,7 +35,7 @@ pub(super) fn generate_invalidates<'cx, 'gcx, 'tcx>(
     mir: &Mir<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
 ) {
-    if !all_facts.is_some() {
+    if all_facts.is_none() {
         // Nothing to do if we don't have any facts
         return;
     }

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs

@@ -566,10 +566,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             | hir::LifetimeName::Underscore => {
                 let region_name = self.synthesize_region_name(counter);
                 let ampersand_span = lifetime.span;
-                return Some(RegionName {
+                Some(RegionName {
                     name: region_name,
                     source: RegionNameSource::MatchedAdtAndSegment(ampersand_span),
-                });
+                })
             }
 
             hir::LifetimeName::Implicit => {
@@ -584,7 +584,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 // T>`. We don't consider this a match; instead we let
                 // the "fully elaborated" type fallback above handle
                 // it.
-                return None;
+                None
             }
         }
     }