refactor(transformer): pre-allocate more stack space

crates/oxc_transformer/src/es2015/arrow_functions.rs

@@ -151,7 +151,7 @@ pub struct ArrowFunctions<'a> {
 impl<'a> ArrowFunctions<'a> {
     pub fn new(options: ArrowFunctionsOptions) -> Self {
         // `SparseStack` is created with 1 empty entry, for `Program`
-        Self { _options: options, this_var_stack: SparseStack::new() }
+        Self { _options: options, this_var_stack: SparseStack::with_capacity(16, 0) }
     }
 }
 

crates/oxc_transformer/src/es2016/exponentiation_operator.rs

@@ -57,7 +57,7 @@ struct Exploded<'a> {
 
 impl<'a> ExponentiationOperator<'a> {
     pub fn new() -> Self {
-        Self { var_declarations: SparseStack::new() }
+        Self { var_declarations: SparseStack::with_capacity(16, 0) }
     }
 }
 

crates/oxc_transformer/src/es2020/nullish_coalescing_operator.rs

@@ -43,7 +43,7 @@ pub struct NullishCoalescingOperator<'a> {
 
 impl<'a> NullishCoalescingOperator<'a> {
     pub fn new() -> Self {
-        Self { var_declarations: SparseStack::new() }
+        Self { var_declarations: SparseStack::with_capacity(16, 0) }
     }
 }
 

crates/oxc_transformer/src/es2021/logical_assignment_operators.rs

@@ -68,7 +68,7 @@ pub struct LogicalAssignmentOperators<'a> {
 
 impl<'a> LogicalAssignmentOperators<'a> {
     pub fn new() -> Self {
-        Self { var_declarations: SparseStack::new() }
+        Self { var_declarations: SparseStack::with_capacity(16, 0) }
     }
 }
 

crates/oxc_transformer/src/helpers/stack/sparse.rs

@@ -51,6 +51,7 @@ impl<T> SparseStack<T> {
     ///
     /// # Panics
     /// Panics if `T` is a zero-sized type.
+    #[expect(dead_code)]
     pub fn new() -> Self {
         // `has_values` starts with a single empty entry, which will never be popped off.
         // This means `take_last`, `last_or_init`, and `last_mut_or_init` can all be infallible,
@@ -70,7 +71,6 @@ impl<T> SparseStack<T> {
     /// * `total_capacity` must not exceed `Self::MAX_TOTAL_CAPACITY`.
     /// * `filled_capacity` must not exceed `Self::MAX_FILLED_CAPACITY`.
     #[inline]
-    #[expect(dead_code)]
     pub fn with_capacity(total_capacity: usize, filled_capacity: usize) -> Self {
         Self {
             has_values: NonEmptyStack::with_capacity(total_capacity, false),