Fix multiple Default implementation caveats

framework/aster-frame/src/arch/x86/cpu.rs

@@ -236,6 +236,7 @@ impl UserPreemption {
     const PREEMPTION_INTERVAL: u32 = 100;
 
     /// Creates a new instance of `UserPreemption`.
+    #[allow(clippy::new_without_default)]
     pub const fn new() -> Self {
         UserPreemption { count: 0 }
     }

framework/aster-frame/src/sync/wait.rs

@@ -146,6 +146,12 @@ impl WaitQueue {
     }
 }
 
+impl Default for WaitQueue {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// A waiter that can put the current thread to sleep until it is woken up by the associated
 /// [`Waker`].
 ///

kernel/aster-nix/src/device/tty/driver.rs

@@ -73,6 +73,12 @@ impl TtyDriver {
     }
 }
 
+impl Default for TtyDriver {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 fn console_input_callback(mut reader: VmReader) {
     let tty_driver = get_tty_driver();
     while reader.remain() > 0 {

kernel/aster-nix/src/events/subject.rs

@@ -85,3 +85,9 @@ impl<E: Events, F: EventsFilter<E>> Subject<E, F> {
         });
     }
 }
+
+impl<E: Events> Default for Subject<E> {
+    fn default() -> Self {
+        Self::new()
+    }
+}

kernel/aster-nix/src/fs/file_table.rs

@@ -198,6 +198,12 @@ impl FileTable {
     }
 }
 
+impl Default for FileTable {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl Clone for FileTable {
     fn clone(&self) -> Self {
         Self {

kernel/aster-nix/src/process/process_vm/heap.rs

@@ -97,3 +97,9 @@ impl Clone for Heap {
         }
     }
 }
+
+impl Default for Heap {
+    fn default() -> Self {
+        Self::new()
+    }
+}

kernel/libs/aster-util/src/slot_vec.rs

@@ -5,6 +5,7 @@ use alloc::vec::Vec;
 /// SlotVec is the variant of Vector.
 /// It guarantees that the index of one item remains unchanged during adding
 /// or deleting other items of the vector.
+#[derive(Debug, Clone)]
 pub struct SlotVec<T> {
     // The slots to store items.
     slots: Vec<Option<T>>,
@@ -118,11 +119,8 @@ impl<T> SlotVec<T> {
     }
 }
 
-impl<T: Clone> Clone for SlotVec<T> {
-    fn clone(&self) -> Self {
-        Self {
-            slots: self.slots.clone(),
-            num_occupied: self.num_occupied,
-        }
+impl Default for SlotVec<()> {
+    fn default() -> Self {
+        Self::new()
     }
 }