refactor(data_structures): add len method to StackCommon trait (#6215)

`len` method is in common between all stack types. Move it into `StackCommon` trait.

crates/oxc_data_structures/src/stack/common.rs

@@ -11,7 +11,7 @@ use assert_unchecked::assert_unchecked;
 use super::{NonNull, StackCapacity};
 
 pub trait StackCommon<T>: StackCapacity<T> {
-    // Getter setter methods defined by implementer
+    // Getter + setter methods defined by implementer
     fn start(&self) -> NonNull<T>;
     fn end(&self) -> NonNull<T>;
     fn cursor(&self) -> NonNull<T>;
@@ -19,6 +19,9 @@ pub trait StackCommon<T>: StackCapacity<T> {
     fn set_end(&mut self, end: NonNull<T>);
     fn set_cursor(&mut self, cursor: NonNull<T>);
 
+    // Defined by implementer
+    fn len(&self) -> usize;
+
     /// Make allocation of `capacity_bytes` bytes, aligned for `T`.
     ///
     /// # Panics
@@ -98,12 +101,12 @@ pub trait StackCommon<T>: StackCapacity<T> {
     ///
     /// # SAFETY
     /// * Stack must be allocated.
-    /// * Stack must contain `len` initialized entries, starting at `self.start()`.
+    /// * Stack must contain `self.len()` initialized entries, starting at `self.start()`.
     #[inline]
-    unsafe fn drop_contents(&self, len: usize) {
+    unsafe fn drop_contents(&self) {
         // Drop contents. Next line copied from `std`'s `Vec`.
         // SAFETY: Caller guarantees stack contains `len` initialized entries, starting at `start`.
-        ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.start().as_ptr(), len));
+        ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.start().as_ptr(), self.len()));
     }
 
     /// Get layout for allocation of `capacity_bytes` bytes.

crates/oxc_data_structures/src/stack/non_empty.rs

@@ -86,6 +86,19 @@ impl<T> StackCommon<T> for NonEmptyStack<T> {
     fn set_cursor(&mut self, cursor: NonNull<T>) {
         self.cursor = cursor;
     }
+
+    #[inline]
+    fn len(&self) -> usize {
+        // SAFETY: `self.start` and `self.cursor` are both derived from same pointer.
+        // `self.cursor` is always >= `self.start`.
+        // Distance between pointers is always a multiple of `size_of::<T>()`.
+        let offset = unsafe { self.cursor_offset() };
+
+        // When stack has 1 entry, `start - cursor == 0`, so add 1 to get number of entries.
+        // SAFETY: Capacity cannot exceed `Self::MAX_CAPACITY`, which is `<= isize::MAX`,
+        // and offset can't exceed capacity, so `+ 1` cannot wrap around.
+        offset + 1
+    }
 }
 
 impl<T> NonEmptyStack<T> {
@@ -275,15 +288,7 @@ impl<T> NonEmptyStack<T> {
     /// Number of entries is always at least 1. Stack is never empty.
     #[inline]
     pub fn len(&self) -> usize {
-        // SAFETY: `self.start` and `self.cursor` are both derived from same pointer.
-        // `self.cursor` is always >= `self.start`.
-        // Distance between pointers is always a multiple of `size_of::<T>()`.
-        let offset = unsafe { self.cursor_offset() };
-
-        // When stack has 1 entry, `start - cursor == 0`, so add 1 to get number of entries.
-        // SAFETY: Capacity cannot exceed `Self::MAX_CAPACITY`, which is `<= isize::MAX`,
-        // and offset can't exceed capacity, so `+ 1` cannot wrap around.
-        offset + 1
+        <Self as StackCommon<T>>::len(self)
     }
 
     #[inline]
@@ -303,7 +308,7 @@ impl<T> Drop for NonEmptyStack<T> {
         // Drop contents.
         // SAFETY: Stack is always allocated, and contains `self.len()` initialized entries,
         // starting at `self.start`.
-        unsafe { self.drop_contents(self.len()) };
+        unsafe { self.drop_contents() };
 
         // Drop the memory
         // SAFETY: Stack is always allocated.

crates/oxc_data_structures/src/stack/standard.rs

@@ -74,6 +74,13 @@ impl<T> StackCommon<T> for Stack<T> {
     fn set_cursor(&mut self, cursor: NonNull<T>) {
         self.cursor = cursor;
     }
+
+    fn len(&self) -> usize {
+        // SAFETY: `self.start` and `self.cursor` are both derived from same pointer.
+        // `self.cursor` is always >= `self.start`.
+        // Distance between pointers is always a multiple of `size_of::<T>()`.
+        unsafe { self.cursor_offset() }
+    }
 }
 
 impl<T> Stack<T> {
@@ -303,10 +310,7 @@ impl<T> Stack<T> {
     /// Get number of entries on stack.
     #[inline]
     pub fn len(&self) -> usize {
-        // SAFETY: `self.start` and `self.cursor` are both derived from same pointer.
-        // `self.cursor` is always >= `self.start`.
-        // Distance between pointers is always a multiple of `size_of::<T>()`.
-        unsafe { self.cursor_offset() }
+        <Self as StackCommon<T>>::len(self)
     }
 
     /// Get if stack is empty.
@@ -332,7 +336,7 @@ impl<T> Drop for Stack<T> {
         if !self.is_empty() {
             // SAFETY: Checked above that stack is allocated.
             // Stack contains `self.len()` initialized entries, starting at `self.start`
-            unsafe { self.drop_contents(self.len()) };
+            unsafe { self.drop_contents() };
         }
 
         // Drop the memory