two clippy changes

optd-core/src/cascades/memo.rs

@@ -204,13 +204,10 @@ impl<T: RelNodeTyp> Memo<T> {
         group_id: ReducedGroupId,
         memo_node: RelMemoNode<T>,
     ) {
-        match self.groups.entry(group_id) {
-            Entry::Occupied(mut entry) => {
-                let group = entry.get_mut();
-                group.group_exprs.insert(expr_id);
-                return;
-            }
-            _ => {}
+        if let Entry::Occupied(mut entry) = self.groups.entry(group_id) {
+            let group = entry.get_mut();
+            group.group_exprs.insert(expr_id);
+            return;
         }
         let mut group = Group {
             group_exprs: HashSet::new(),
@@ -423,8 +420,7 @@ impl<T: RelNodeTyp> Memo<T> {
             if !winner.impossible {
                 let expr_id = winner.expr_id;
                 let expr = self.get_expr_memoed(expr_id);
-                let mut children = Vec::new();
-                children.reserve(expr.children.len());
+                let mut children = Vec::with_capacity(expr.children.len());
                 for child in &expr.children {
                     children.push(self.get_best_group_binding(*child, on_produce)?);
                 }

optd-core/src/cascades/tasks/optimize_inputs.rs

@@ -51,8 +51,7 @@ impl OptimizeInputsTask {
         optimizer: &mut CascadesOptimizer<T>,
     ) -> Vec<Cost> {
         let zero_cost = optimizer.cost().zero();
-        let mut input_cost = Vec::new();
-        input_cost.reserve(children.len());
+        let mut input_cost = Vec::with_capacity(children.len());
         for &child in children.iter() {
             let group = optimizer.get_group_info(child);
             if let Some(ref winner) = group.winner {

optd-datafusion-repr/src/properties/schema.rs

@@ -10,6 +10,10 @@ impl Schema {
     pub fn len(&self) -> usize {
         self.0.len()
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 pub trait Catalog: Send + Sync + 'static {