refactor(transformer/class-properties): re-order fields and expand comments

crates/oxc_transformer/src/es2022/class_properties/class.rs

@@ -385,6 +385,8 @@ impl<'a> ClassProperties<'a, '_> {
         if class_details.is_transform_required {
             self.transform_class_declaration_on_exit_impl(class, ctx);
         } else {
+            // Note: `is_transform_required` is `true` if class has any private properties/methods,
+            // so no need to touch `private_field_count` here
             debug_assert!(class_details.bindings.temp.is_none());
         }
         // Pop off stack. We're done!
@@ -446,6 +448,7 @@ impl<'a> ClassProperties<'a, '_> {
 
         if let Some(private_props) = &class_details.private_props {
             self.private_field_count -= private_props.len();
+
             if self.private_fields_as_properties {
                 let mut private_props = private_props
                     .iter()
@@ -536,6 +539,8 @@ impl<'a> ClassProperties<'a, '_> {
         if class_details.is_transform_required {
             self.transform_class_expression_on_exit_impl(expr, ctx);
         } else {
+            // Note: `is_transform_required` is `true` if class has any private properties/methods,
+            // so no need to touch `private_field_count` here
             debug_assert!(class_details.bindings.temp.is_none());
         }
 
@@ -591,6 +596,7 @@ impl<'a> ClassProperties<'a, '_> {
         // Also insert `var _prop;` temp var declarations for private static props.
         if let Some(private_props) = &class_details.private_props {
             self.private_field_count -= private_props.len();
+
             // Insert `var _prop;` declarations here rather than when binding was created to maintain
             // same order of `var` declarations as Babel.
             // `c = class C { #x = 1; static y = 2; }` -> `var _C, _x;`

crates/oxc_transformer/src/es2022/class_properties/mod.rs

@@ -261,6 +261,8 @@ pub struct ClassProperties<'a, 'ctx> {
     /// This problem only affects class expressions. Class declarations aren't affected,
     /// as their exit-phase transform happens in `exit_class`.
     classes_stack: ClassesStack<'a>,
+    /// Count of private fields in current class and parent classes.
+    private_field_count: usize,
 
     // ----- State used only during enter phase -----
     //
@@ -277,8 +279,6 @@ pub struct ClassProperties<'a, 'ctx> {
     /// Keys are symbols' IDs.
     /// Values are initially the original name of binding, later on the name of new UID name.
     clashing_constructor_symbols: FxHashMap<SymbolId, Atom<'a>>,
-    /// Count of private fields in class and also included parent classes.
-    private_field_count: usize,
 
     // ----- State used only during exit phase -----
     //
@@ -309,12 +309,12 @@ impl<'a, 'ctx> ClassProperties<'a, 'ctx> {
             transform_static_blocks,
             ctx,
             classes_stack: ClassesStack::new(),
+            private_field_count: 0,
             // Temporary values - overwritten when entering class
             instance_inits_scope_id: ScopeId::new(0),
             instance_inits_constructor_scope_id: None,
             // `Vec`s and `FxHashMap`s which are reused for every class being transformed
             clashing_constructor_symbols: FxHashMap::default(),
-            private_field_count: 0,
             insert_before: vec![],
             insert_after_exprs: vec![],
             insert_after_stmts: vec![],
@@ -342,7 +342,9 @@ impl<'a> Traverse<'a> for ClassProperties<'a, '_> {
     // `#[inline]` for fast exit for expressions which are not any of the transformed types
     #[inline]
     fn enter_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
-        // Return early if no private fields are found.
+        // All of transforms below only act on `PrivateFieldExpression`s or `PrivateInExpression`s.
+        // If we're not inside a class which has private fields, `#prop` can't be present here,
+        // so exit early - fast path for common case.
         if self.private_field_count == 0 {
             return;
         }