edit for clippy check

Author: surechen

clippy_lints/src/shadow.rs

@@ -123,7 +123,7 @@ impl<'tcx> LateLintPass<'tcx> for Shadow {
                 return;
             }
 
-            if self.skip.len() > 0 && self.skip.last_mut().unwrap().contains(&ident.name) {
+            if !self.skip.is_empty() && self.skip.last_mut().unwrap().contains(&ident.name) {
                 // skip async function's params
                 return;
             }
@@ -166,10 +166,10 @@ impl<'tcx> LateLintPass<'tcx> for Shadow {
             if let Some(header) = match kind {
                 FnKind::ItemFn(_, _, header, _) => Some(header),
                 FnKind::Method(_, sig, _) => Some(sig.header),
-                _ => None,
+                FnKind::Closure => None,
             };
             if header.asyncness == IsAsync::Async;
-            if body.params.len() > 0;
+            if !body.params.is_empty();
             then {
                 self.skip.push(FxHashSet::default());
                 let skip_params = self.skip.last_mut().unwrap();
@@ -195,10 +195,10 @@ impl<'tcx> LateLintPass<'tcx> for Shadow {
             if let Some(header) = match kind {
                 FnKind::ItemFn(_, _, header, _) => Some(header),
                 FnKind::Method(_, sig, _) => Some(sig.header),
-                _ => None,
+                FnKind::Closure => None,
             };
             if header.asyncness == IsAsync::Async;
-            if body.params.len() > 0;
+            if !body.params.is_empty();
             then {
                 self.skip.pop();
             }