oxc_transformer 0.136.0

//! ES2018 object spread transformation.
//!
//! This plugin transforms rest properties for object destructuring assignment and spread properties for object literals.
//!
//! > This plugin is included in `preset-env`, in ES2018
//!
//! ## Example
//!
//! Input:
//! ```js
//! var x = { a: 1, b: 2 };
//! var y = { ...x, c: 3 };
//! ```
//!
//! Output:
//! ```js
//! var x = { a: 1, b: 2 };
//! var y = _objectSpread({}, x, { c: 3 });
//! ```
//!
//! ## Implementation
//!
//! Implementation based on [@babel/plugin-transform-object-rest-spread](https://babeljs.io/docs/babel-plugin-transform-object-rest-spread).
//!
//! ## References:
//!
//! * Babel plugin implementation: <https://github.com/babel/babel/tree/v7.26.2/packages/babel-plugin-transform-object-rest-spread>
//! * Object rest/spread TC39 proposal: <https://github.com/tc39/proposal-object-rest-spread>

use std::mem;

use serde::Deserialize;

use oxc_allocator::{Address, Box as ArenaBox, GetAddress, TakeIn, Vec as ArenaVec};
use oxc_ast::{NONE, ast::*};
use oxc_diagnostics::OxcDiagnostic;
use oxc_ecmascript::{BoundNames, ToJsString, WithoutGlobalReferenceInformation};
use oxc_semantic::{ScopeFlags, ScopeId, SymbolFlags};
use oxc_span::{GetSpan, SPAN};
use oxc_traverse::{Ancestor, MaybeBoundIdentifier, Traverse};

use crate::{
    common::helper_loader::{Helper, helper_call, helper_call_expr, helper_load},
    context::TraverseCtx,
    state::TransformState,
};

#[derive(Debug, Default, Clone, Copy, Deserialize)]
#[serde(default, rename_all = "camelCase")]
pub struct ObjectRestSpreadOptions {
    pub loose: bool,

    pub use_built_ins: bool,
}

pub struct ObjectRestSpread<'a> {
    options: ObjectRestSpreadOptions,

    excluded_variable_declarators: Vec<VariableDeclarator<'a>>,
}

impl<'a> ObjectRestSpread<'a> {
    pub fn new(options: ObjectRestSpreadOptions, state: &mut TransformState<'a>) -> Self {
        if options.loose {
            state.error(OxcDiagnostic::error(
                "Option `loose` is not implemented for object-rest-spread.",
            ));
        }
        if options.use_built_ins {
            state.error(OxcDiagnostic::error(
                "Option `useBuiltIns` is not implemented for object-rest-spread.",
            ));
        }
        if state.assumptions.object_rest_no_symbols {
            state.error(OxcDiagnostic::error(
                "Compiler assumption `objectRestNoSymbols` is not implemented for object-rest-spread.",
            ));
        }
        if state.assumptions.ignore_function_length {
            state.error(OxcDiagnostic::error(
                "Compiler assumption `ignoreFunctionLength` is not implemented for object-rest-spread.",
            ));
        }
        Self { options, excluded_variable_declarators: vec![] }
    }
}

impl<'a> Traverse<'a, TransformState<'a>> for ObjectRestSpread<'a> {
    // For excluded keys when destructuring inside a function.
    // `function foo() { ({a, ...b} = c) }` -> `const _excluded = ["a"]; function foo() { ... }`
    fn exit_program(&mut self, _node: &mut Program<'a>, ctx: &mut TraverseCtx<'a>) {
        if !self.excluded_variable_declarators.is_empty() {
            let declarators = ctx.ast.vec_from_iter(self.excluded_variable_declarators.drain(..));
            let kind = VariableDeclarationKind::Const;
            let declaration = ctx.ast.alloc_variable_declaration(SPAN, kind, declarators, false);
            let statement = Statement::VariableDeclaration(declaration);
            ctx.state.top_level_statements.insert_statement(statement);
        }
    }

    // `({ x, ..y })`.
    // `({ x, ..y } = foo)`.
    // `([{ x, ..y }] = foo)`.
    #[inline]
    fn enter_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
        match expr {
            Expression::ObjectExpression(_) => {
                Self::transform_object_expression(self.options, expr, ctx);
            }
            Expression::AssignmentExpression(_) => {
                self.transform_assignment_expression(expr, ctx);
            }
            _ => {}
        }
    }

    // `(...x) => {}`.
    #[inline]
    fn enter_arrow_function_expression(
        &mut self,
        arrow: &mut ArrowFunctionExpression<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        Self::transform_arrow(arrow, ctx);
    }

    // `function foo({...x}) {}`.
    #[inline]
    fn enter_function(&mut self, func: &mut Function<'a>, ctx: &mut TraverseCtx<'a>) {
        Self::transform_function(func, ctx);
    }

    // `let { x, ..y } = foo`.
    // `let [{ x, ..y }] = foo`
    // Includes `for (var {...x} = 1;;);`
    #[inline]
    fn enter_variable_declaration(
        &mut self,
        decl: &mut VariableDeclaration<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        self.transform_variable_declaration(decl, ctx);
    }

    // Transform `try {} catch (...x) {}`.
    #[inline]
    fn enter_catch_clause(&mut self, clause: &mut CatchClause<'a>, ctx: &mut TraverseCtx<'a>) {
        if clause.param.is_some() {
            Self::transform_catch_clause(clause, ctx);
        }
    }

    // `for ({...x} in []);` `for ({...x} of []);`
    // `for ([{...x}] in []);` `for ([{...x}] of []);`
    #[inline]
    fn enter_for_in_statement(&mut self, stmt: &mut ForInStatement<'a>, ctx: &mut TraverseCtx<'a>) {
        let scope_id = stmt.scope_id();
        match &mut stmt.left {
            ForStatementLeft::VariableDeclaration(decl) => {
                let body = &mut stmt.body;
                Self::transform_variable_declaration_for_x_statement(decl, body, scope_id, ctx);
            }
            _ => {
                Self::transform_for_statement_left(scope_id, &mut stmt.left, &mut stmt.body, ctx);
            }
        }
    }

    // `for ({...x} in []);` `for ({...x} of []);`
    // `for ([{...x}] in []);` `for ([{...x}] of []);`
    #[inline]
    fn enter_for_of_statement(&mut self, stmt: &mut ForOfStatement<'a>, ctx: &mut TraverseCtx<'a>) {
        let scope_id = stmt.scope_id();
        match &mut stmt.left {
            ForStatementLeft::VariableDeclaration(decl) => {
                let body = &mut stmt.body;
                Self::transform_variable_declaration_for_x_statement(decl, body, scope_id, ctx);
            }
            _ => {
                Self::transform_for_statement_left(scope_id, &mut stmt.left, &mut stmt.body, ctx);
            }
        }
    }
}

impl<'a> ObjectRestSpread<'a> {
    // Transform `({ x, ..y } = foo)`.
    // Transform `([{ x, ..y }] = foo)`.
    fn transform_assignment_expression(
        &mut self,
        expr: &mut Expression<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        let Expression::AssignmentExpression(assign_expr) = expr else { unreachable!() };
        // Allow `{...x} = {}` and `[{...x}] = []`.
        if !Self::has_nested_target_rest(&assign_expr.left) {
            return;
        }

        // If not an top `({ ...y })`, walk the pattern and create references for all the objects with a rest.
        if !matches!(&assign_expr.left, AssignmentTarget::ObjectAssignmentTarget(t) if t.rest.is_some())
        {
            self.walk_and_replace_nested_object_target(expr, ctx);
            return;
        }

        let kind = VariableDeclarationKind::Var;
        let symbol_flags = kind_to_symbol_flags(kind);
        let scope_id = ctx.current_hoist_scope_id();
        let mut reference_builder =
            ReferenceBuilder::new(&mut assign_expr.right, symbol_flags, scope_id, true, ctx);
        let state = State::new(kind, symbol_flags, scope_id);

        let mut new_decls = vec![];

        if let Some(id) = reference_builder.binding.take() {
            new_decls.push(ctx.ast.variable_declarator(SPAN, state.kind, id, NONE, None, false));
        }

        let data = Self::walk_assignment_target(&mut assign_expr.left, &mut new_decls, state, ctx);

        Self::insert_var_declaration_before_containing_statement(new_decls, ctx);

        // Make an sequence expression.
        let mut expressions = ctx.ast.vec();
        let op = AssignmentOperator::Assign;

        // Insert `_foo = rhs`
        if let Some(expr) = reference_builder.expr.take() {
            expressions.push(ctx.ast.expression_assignment(
                SPAN,
                op,
                reference_builder.maybe_bound_identifier.create_write_target(ctx),
                expr,
            ));
        }

        // Insert `{} = _foo`
        expressions.push(ctx.ast.expression_assignment(
            SPAN,
            op,
            assign_expr.left.take_in(ctx.ast),
            reference_builder.create_read_expression(ctx),
        ));

        // Insert all `rest = _extends({}, (_objectDestructuringEmpty(_foo), _foo))`
        for datum in data {
            let (lhs, rhs) = datum.get_lhs_rhs(
                &mut reference_builder,
                &mut self.excluded_variable_declarators,
                ctx,
            );
            if let BindingPatternOrAssignmentTarget::AssignmentTarget(lhs) = lhs {
                expressions.push(ctx.ast.expression_assignment(SPAN, op, lhs, rhs));
            }
        }

        // Insert final read `_foo` only if the expression result is consumed.
        // e.g. remove for `({ a2, ...b2 } = c2)`, keep for `(x, ({ a2, ...b2 } = c2))`.
        let is_expression_statement = ctx
            .ancestors()
            .find(|a| !matches!(a, Ancestor::ParenthesizedExpressionExpression(_)))
            .is_some_and(|a| matches!(a, Ancestor::ExpressionStatementExpression(_)));
        if !is_expression_statement {
            expressions.push(reference_builder.create_read_expression(ctx));
        }

        *expr = ctx.ast.expression_sequence(assign_expr.span, expressions);
    }

    fn walk_assignment_target(
        target: &mut AssignmentTarget<'a>,
        new_decls: &mut Vec<VariableDeclarator<'a>>,
        state: State,
        ctx: &mut TraverseCtx<'a>,
    ) -> Vec<SpreadPair<'a>> {
        match target {
            AssignmentTarget::ObjectAssignmentTarget(t) => {
                let mut data = vec![];
                for prop in &mut t.properties {
                    if let AssignmentTargetProperty::AssignmentTargetPropertyProperty(p) = prop {
                        data.extend(match &mut p.binding {
                            AssignmentTargetMaybeDefault::AssignmentTargetWithDefault(t) => {
                                Self::walk_assignment_target(&mut t.binding, new_decls, state, ctx)
                            }
                            _ => Self::walk_assignment_target(
                                p.binding.to_assignment_target_mut(),
                                new_decls,
                                state,
                                ctx,
                            ),
                        });
                    }
                }
                if let Some(datum) =
                    Self::transform_object_assignment_target(t, new_decls, state, ctx)
                {
                    data.push(datum);
                }
                data
            }
            _ => vec![],
        }
    }

    fn transform_object_assignment_target(
        object_assignment_target: &mut ObjectAssignmentTarget<'a>,
        new_decls: &mut Vec<VariableDeclarator<'a>>,
        state: State,
        ctx: &mut TraverseCtx<'a>,
    ) -> Option<SpreadPair<'a>> {
        let rest = object_assignment_target.rest.take()?;
        let rest_target = rest.unbox().target;
        let mut all_primitives = true;
        let keys =
            ctx.ast.vec_from_iter(object_assignment_target.properties.iter_mut().filter_map(|e| {
                match e {
                    AssignmentTargetProperty::AssignmentTargetPropertyIdentifier(ident) => {
                        let name = ident.binding.name;
                        let expr = ctx.ast.expression_string_literal(SPAN, name, None);
                        Some(ArrayExpressionElement::from(expr))
                    }
                    AssignmentTargetProperty::AssignmentTargetPropertyProperty(p) => {
                        Self::transform_property_key(
                            &mut p.name,
                            new_decls,
                            &mut all_primitives,
                            state,
                            ctx,
                        )
                    }
                }
            }));
        Some(SpreadPair {
            lhs: BindingPatternOrAssignmentTarget::AssignmentTarget(rest_target),
            keys,
            has_no_properties: object_assignment_target.is_empty(),
            all_primitives,
        })
    }

    fn has_nested_target_rest(target: &AssignmentTarget<'a>) -> bool {
        match target {
            AssignmentTarget::ObjectAssignmentTarget(t) => {
                t.rest.is_some()
                    || t.properties.iter().any(|p| match p {
                        AssignmentTargetProperty::AssignmentTargetPropertyIdentifier(_) => false,
                        AssignmentTargetProperty::AssignmentTargetPropertyProperty(p) => {
                            match &p.binding {
                                AssignmentTargetMaybeDefault::AssignmentTargetWithDefault(t) => {
                                    Self::has_nested_target_rest(&t.binding)
                                }
                                _ => Self::has_nested_target_rest(p.binding.to_assignment_target()),
                            }
                        }
                    })
            }
            AssignmentTarget::ArrayAssignmentTarget(t) => {
                t.elements.iter().flatten().any(|e| match e {
                    AssignmentTargetMaybeDefault::AssignmentTargetWithDefault(t) => {
                        Self::has_nested_target_rest(&t.binding)
                    }
                    _ => Self::has_nested_target_rest(e.to_assignment_target()),
                }) || t.rest.as_ref().is_some_and(|r| Self::has_nested_target_rest(&r.target))
            }
            _ => false,
        }
    }

    #[expect(clippy::unused_self)]
    fn walk_and_replace_nested_object_target(
        &self,
        expr: &mut Expression<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        let Expression::AssignmentExpression(assign_expr) = expr else {
            return;
        };
        let mut decls = vec![];
        let mut exprs = vec![];
        Self::recursive_walk_assignment_target(&mut assign_expr.left, &mut decls, &mut exprs, ctx);
        Self::insert_var_declaration_before_containing_statement(decls, ctx);
        let mut expressions = ctx.ast.vec1(expr.take_in(ctx.ast));
        expressions.extend(exprs);
        *expr = ctx.ast.expression_sequence(SPAN, expressions);
    }

    // Insert `var _foo` before the statement that contains the transformed assignment.
    // The assignment can appear in an expression statement, but also in places like
    // computed binding keys: `const { [({ ...rest } = {})]: value } = {};`.
    fn insert_var_declaration_before_containing_statement(
        decls: Vec<VariableDeclarator<'a>>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        if decls.is_empty() {
            return;
        }

        let Some(address) = Self::containing_statement_address(ctx) else { return };
        let kind = VariableDeclarationKind::Var;
        let declaration =
            ctx.ast.alloc_variable_declaration(SPAN, kind, ctx.ast.vec_from_iter(decls), false);
        let statement = Statement::VariableDeclaration(declaration);
        ctx.state.statement_injector.insert_before(&address, statement);
    }

    fn containing_statement_address(ctx: &TraverseCtx<'a>) -> Option<Address> {
        let mut address = None;
        for ancestor in ctx.ancestors() {
            if matches!(
                ancestor,
                Ancestor::ProgramBody(_)
                    | Ancestor::BlockStatementBody(_)
                    | Ancestor::FunctionBodyStatements(_)
                    | Ancestor::StaticBlockBody(_)
                    | Ancestor::SwitchCaseConsequent(_)
                    | Ancestor::TSModuleBlockBody(_)
            ) {
                break;
            }
            address = Some(ancestor.address());
        }
        address
    }

    fn recursive_walk_assignment_target(
        pat: &mut AssignmentTarget<'a>,
        decls: &mut Vec<VariableDeclarator<'a>>,
        exprs: &mut Vec<Expression<'a>>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        match pat {
            AssignmentTarget::ArrayAssignmentTarget(t) => {
                for e in t.elements.iter_mut().flatten() {
                    Self::recursive_walk_assignment_target_maybe_default(e, decls, exprs, ctx);
                }
            }
            AssignmentTarget::ObjectAssignmentTarget(t) => {
                for p in &mut t.properties {
                    if let AssignmentTargetProperty::AssignmentTargetPropertyProperty(e) = p {
                        Self::recursive_walk_assignment_target_maybe_default(
                            &mut e.binding,
                            decls,
                            exprs,
                            ctx,
                        );
                    }
                }
                if t.rest.is_none() {
                    return;
                }
                let bound_identifier = ctx.generate_uid_in_current_hoist_scope("ref");
                let id = bound_identifier.create_binding_pattern(ctx);
                let kind = VariableDeclarationKind::Var;
                decls.push(ctx.ast.variable_declarator(SPAN, kind, id, NONE, None, false));
                exprs.push(ctx.ast.expression_assignment(
                    SPAN,
                    AssignmentOperator::Assign,
                    pat.take_in(ctx.ast),
                    bound_identifier.create_read_expression(ctx),
                ));
                *pat = bound_identifier.create_spanned_write_target(SPAN, ctx);
            }
            _ => {}
        }
    }

    fn recursive_walk_assignment_target_maybe_default(
        target: &mut AssignmentTargetMaybeDefault<'a>,
        decls: &mut Vec<VariableDeclarator<'a>>,
        exprs: &mut Vec<Expression<'a>>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        match target {
            AssignmentTargetMaybeDefault::AssignmentTargetWithDefault(d) => {
                Self::recursive_walk_assignment_target(&mut d.binding, decls, exprs, ctx);
            }
            _ => Self::recursive_walk_assignment_target(
                target.to_assignment_target_mut(),
                decls,
                exprs,
                ctx,
            ),
        }
    }
}

impl<'a> ObjectRestSpread<'a> {
    // Transform `({ x, ..y })`.
    // `pub` for jsx spread.
    pub fn transform_object_expression(
        _options: ObjectRestSpreadOptions,
        expr: &mut Expression<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        let Expression::ObjectExpression(obj_expr) = expr else { unreachable!() };

        if obj_expr.properties.iter().all(|prop| !prop.is_spread()) {
            return;
        }

        let span = obj_expr.span;
        let mut call_expr: Option<ArenaBox<'a, CallExpression<'a>>> = None;
        let mut props = ctx.ast.vec_with_capacity(obj_expr.properties.len());

        for prop in obj_expr.properties.drain(..) {
            if let ObjectPropertyKind::SpreadProperty(mut spread_prop) = prop {
                Self::make_object_spread(&mut call_expr, &mut props, ctx);
                let arg = spread_prop.argument.take_in(ctx.ast);
                call_expr.as_mut().unwrap().arguments.push(Argument::from(arg));
            } else {
                props.push(prop);
            }
        }

        if !props.is_empty() {
            Self::make_object_spread(&mut call_expr, &mut props, ctx);
        }

        let mut final_call = call_expr.unwrap();
        final_call.span = span;
        *expr = Expression::CallExpression(final_call);
    }

    fn make_object_spread(
        expr: &mut Option<ArenaBox<'a, CallExpression<'a>>>,
        props: &mut ArenaVec<'a, ObjectPropertyKind<'a>>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        let had_props = !props.is_empty();
        let obj = ctx.ast.expression_object(
            SPAN,
            // Reserve maximize might be used space for new vec
            mem::replace(props, ctx.ast.vec_with_capacity(props.capacity() - props.len())),
        );
        let arguments = if let Some(call_expr) = expr.take() {
            let arg = Expression::CallExpression(call_expr);
            let arg = Argument::from(arg);
            if had_props {
                let empty_object = ctx.ast.expression_object(SPAN, ctx.ast.vec());
                ctx.ast.vec_from_array([arg, Argument::from(empty_object), Argument::from(obj)])
            } else {
                ctx.ast.vec1(arg)
            }
        } else {
            ctx.ast.vec1(Argument::from(obj))
        };
        let new_expr = helper_call(Helper::ObjectSpread2, arguments, ctx);
        expr.replace(ctx.ast.alloc(new_expr));
    }
}

impl<'a> ObjectRestSpread<'a> {
    // Transform `function foo({...x}) {}`.
    fn transform_function(func: &mut Function<'a>, ctx: &mut TraverseCtx<'a>) {
        let scope_id = func.scope_id();
        let Some(body) = func.body.as_mut() else { return };
        for param in &mut func.params.items {
            if Self::has_nested_object_rest(&param.pattern) {
                Self::replace_rest_element(
                    VariableDeclarationKind::Var,
                    &mut param.pattern,
                    &mut body.statements,
                    scope_id,
                    ctx,
                );
            }
        }
    }

    // Transform `(...x) => {}`.
    fn transform_arrow(arrow: &mut ArrowFunctionExpression<'a>, ctx: &mut TraverseCtx<'a>) {
        let scope_id = arrow.scope_id();
        for param in &mut arrow.params.items {
            if Self::has_nested_object_rest(&param.pattern) {
                // `({ ...args }) => { args }`
                if arrow.expression {
                    arrow.expression = false;

                    debug_assert!(arrow.body.statements.len() == 1);

                    let Statement::ExpressionStatement(stmt) = arrow.body.statements.pop().unwrap()
                    else {
                        unreachable!(
                            "`arrow.expression` is true, which means it has only one ExpressionStatement."
                        );
                    };
                    let return_stmt =
                        ctx.ast.statement_return(stmt.span, Some(stmt.unbox().expression));
                    arrow.body.statements.push(return_stmt);
                }
                Self::replace_rest_element(
                    VariableDeclarationKind::Var,
                    &mut param.pattern,
                    &mut arrow.body.statements,
                    scope_id,
                    ctx,
                );
            }
        }
    }

    // Transform `try {} catch ({...x}) {}`.
    fn transform_catch_clause(clause: &mut CatchClause<'a>, ctx: &mut TraverseCtx<'a>) {
        let Some(param) = &mut clause.param else { unreachable!() };
        if Self::has_nested_object_rest(&param.pattern) {
            let scope_id = clause.body.scope_id();
            // Remove `SymbolFlags::CatchVariable`.
            param.pattern.bound_names(&mut |ident| {
                ctx.scoping_mut()
                    .symbol_flags_mut(ident.symbol_id())
                    .remove(SymbolFlags::CatchVariable);
            });
            Self::replace_rest_element(
                VariableDeclarationKind::Var,
                &mut param.pattern,
                &mut clause.body.body,
                scope_id,
                ctx,
            );
        }
    }

    // Transform `for (var { ...x };;)`.
    fn transform_variable_declaration_for_x_statement(
        decl: &mut VariableDeclaration<'a>,
        body: &mut Statement<'a>,
        scope_id: ScopeId,
        ctx: &mut TraverseCtx<'a>,
    ) {
        for declarator in &mut decl.declarations {
            if Self::has_nested_object_rest(&declarator.id) {
                let new_scope_id = Self::try_replace_statement_with_block(body, scope_id, ctx);
                let Statement::BlockStatement(block) = body else {
                    unreachable!();
                };
                let bound_symbol_ids = declarator.id.get_symbol_ids();
                let old_scope_id =
                    if decl.kind.is_var() { ctx.current_hoist_scope_id() } else { scope_id };

                Self::replace_rest_element(
                    declarator.kind,
                    &mut declarator.id,
                    &mut block.body,
                    old_scope_id,
                    ctx,
                );

                // Move the bindings from the for init scope to scope of the loop body.
                for symbol_id in bound_symbol_ids {
                    ctx.scoping_mut().move_binding_by_symbol_id(
                        old_scope_id,
                        new_scope_id,
                        symbol_id,
                    );
                }
            }
        }
    }

    // If the assignment target contains an object rest,
    // create a reference and move the assignment target to the block body.
    // `for ({...x} in []);` `for ({...x} of []);`
    // `for ([{...x}] in []);` `for ([{...x}] of []);`
    fn transform_for_statement_left(
        scope_id: ScopeId,
        left: &mut ForStatementLeft<'a>,
        body: &mut Statement<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        if !Self::has_nested_target_rest(left.to_assignment_target()) {
            return;
        }
        let target = left.to_assignment_target_mut();
        let assign_left = target.take_in(ctx.ast);
        let flags = SymbolFlags::FunctionScopedVariable;
        let bound_identifier = ctx.generate_uid("ref", ctx.current_hoist_scope_id(), flags);
        let id = bound_identifier.create_binding_pattern(ctx);
        let kind = VariableDeclarationKind::Var;
        let declarations =
            ctx.ast.vec1(ctx.ast.variable_declarator(SPAN, kind, id, NONE, None, false));
        let decl = ctx.ast.alloc_variable_declaration(SPAN, kind, declarations, false);
        *left = ForStatementLeft::VariableDeclaration(decl);
        Self::try_replace_statement_with_block(body, scope_id, ctx);
        let Statement::BlockStatement(block) = body else {
            unreachable!();
        };
        let operator = AssignmentOperator::Assign;
        let right = bound_identifier.create_read_expression(ctx);
        let expr = ctx.ast.expression_assignment(SPAN, operator, assign_left, right);
        let stmt = ctx.ast.statement_expression(SPAN, expr);
        block.body.insert(0, stmt);
    }

    fn try_replace_statement_with_block(
        stmt: &mut Statement<'a>,
        parent_scope_id: ScopeId,
        ctx: &mut TraverseCtx<'a>,
    ) -> ScopeId {
        if let Statement::BlockStatement(block) = stmt {
            return block.scope_id();
        }
        let scope_id = ctx.create_child_scope(parent_scope_id, ScopeFlags::empty());
        let (span, stmts) = if let Statement::EmptyStatement(empty_stmt) = stmt {
            (empty_stmt.span, ctx.ast.vec())
        } else {
            let span = stmt.span();
            (span, ctx.ast.vec1(stmt.take_in(ctx.ast)))
        };
        *stmt = ctx.ast.statement_block_with_scope_id(span, stmts, scope_id);
        scope_id
    }

    /// Recursively check for object rest.
    fn has_nested_object_rest(pat: &BindingPattern<'a>) -> bool {
        match pat {
            BindingPattern::ObjectPattern(pat) => {
                pat.rest.is_some()
                    || pat.properties.iter().any(|p| Self::has_nested_object_rest(&p.value))
            }
            BindingPattern::ArrayPattern(pat) => {
                pat.elements.iter().any(|e| e.as_ref().is_some_and(Self::has_nested_object_rest))
                    || pat.rest.as_ref().is_some_and(|e| Self::has_nested_object_rest(&e.argument))
            }
            BindingPattern::AssignmentPattern(pat) => Self::has_nested_object_rest(&pat.left),
            BindingPattern::BindingIdentifier(_) => false,
        }
    }

    /// Move the binding to the body if it contains an object rest.
    /// The object pattern will be transform by `transform_object_pattern` afterwards.
    fn replace_rest_element(
        kind: VariableDeclarationKind,
        pattern: &mut BindingPattern<'a>,
        body: &mut ArenaVec<'a, Statement<'a>>,
        scope_id: ScopeId,
        ctx: &mut TraverseCtx<'a>,
    ) {
        match pattern {
            // Replace the object pattern, no need to walk the object properties.
            BindingPattern::ObjectPattern(_) => {
                Self::replace_object_pattern_and_insert_into_block_body(
                    kind, pattern, body, scope_id, ctx,
                );
            }
            BindingPattern::AssignmentPattern(pat) => {
                Self::replace_object_pattern_and_insert_into_block_body(
                    kind,
                    &mut pat.left,
                    body,
                    scope_id,
                    ctx,
                );
            }
            // Or replace all occurrences of object pattern inside array pattern.
            BindingPattern::ArrayPattern(pat) => {
                for element in pat.elements.iter_mut().flatten() {
                    Self::replace_rest_element(kind, element, body, scope_id, ctx);
                }
                if let Some(element) = &mut pat.rest {
                    Self::replace_rest_element(kind, &mut element.argument, body, scope_id, ctx);
                }
            }
            BindingPattern::BindingIdentifier(_) => {}
        }
    }

    // Add `let {...x} = _ref` to body.
    fn replace_object_pattern_and_insert_into_block_body(
        kind: VariableDeclarationKind,
        pat: &mut BindingPattern<'a>,
        body: &mut ArenaVec<'a, Statement<'a>>,
        scope_id: ScopeId,
        ctx: &mut TraverseCtx<'a>,
    ) {
        let decl = Self::create_temporary_reference_for_binding(kind, pat, scope_id, ctx);
        body.insert(0, Statement::VariableDeclaration(ctx.ast.alloc(decl)));
    }

    fn create_temporary_reference_for_binding(
        kind: VariableDeclarationKind,
        pat: &mut BindingPattern<'a>,
        scope_id: ScopeId,
        ctx: &mut TraverseCtx<'a>,
    ) -> VariableDeclaration<'a> {
        let mut flags = kind_to_symbol_flags(kind);
        if matches!(ctx.parent(), Ancestor::TryStatementHandler(_)) {
            // try {} catch (ref) {}
            //               ^^^
            flags |= SymbolFlags::CatchVariable;
        }
        let bound_identifier = ctx.generate_uid("ref", scope_id, flags);
        let kind = VariableDeclarationKind::Let;
        let id = mem::replace(pat, bound_identifier.create_binding_pattern(ctx));
        let init = bound_identifier.create_read_expression(ctx);
        let declarations =
            ctx.ast.vec1(ctx.ast.variable_declarator(SPAN, kind, id, NONE, Some(init), false));
        let decl = ctx.ast.variable_declaration(SPAN, kind, declarations, false);
        decl.bound_names(&mut |ident| {
            *ctx.scoping_mut().symbol_flags_mut(ident.symbol_id()) =
                SymbolFlags::BlockScopedVariable;
        });
        decl
    }
}

impl<'a> ObjectRestSpread<'a> {
    // Transform `let { x, ..y } = foo`.
    // Transform `let [{ x, ..y }] = foo`.
    fn transform_variable_declaration(
        &mut self,
        decl: &mut VariableDeclaration<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) {
        let mut new_decls = vec![];
        for (i, variable_declarator) in decl.declarations.iter_mut().enumerate() {
            if variable_declarator.init.is_some()
                && Self::has_nested_object_rest(&variable_declarator.id)
            {
                let decls = self.transform_variable_declarator(variable_declarator, ctx);
                new_decls.push((i, decls));
            }
        }
        for (i, decls) in new_decls {
            decl.declarations.splice(i..=i, decls);
        }
    }

    // The algorithm depth searches for object rest,
    // and then creates a ref for the object, subsequent visit will then transform this object rest.
    // Transforms:
    // * `var {...a} = foo` -> `var a = _extends({}, (_objectDestructuringEmpty(foo), foo));`
    // * `var [{x: {y: {...a}}}] = z` -> `var [{x: {y: _ref}}] = z, {...a} = _ref`
    fn transform_variable_declarator(
        &mut self,
        decl: &mut VariableDeclarator<'a>,
        ctx: &mut TraverseCtx<'a>,
    ) -> ArenaVec<'a, VariableDeclarator<'a>> {
        // It is syntax error or inside for loop if missing initializer in destructuring pattern.
        let init = decl.init.as_mut().unwrap();

        // Use the scope of the identifier, scope is different for
        // `for (var {...x} = {};;);` and `for (let {...x} = {};;);`
        // TODO: improve this by getting the value only once.
        let mut scope_id = ctx.current_scope_id();
        let mut symbol_flags = kind_to_symbol_flags(decl.kind);
        let symbols = ctx.scoping();
        decl.id.bound_names(&mut |ident| {
            let symbol_id = ident.symbol_id();
            scope_id = symbols.symbol_scope_id(symbol_id);
            symbol_flags.insert(symbols.symbol_flags(symbol_id));
        });

        let state = State::new(decl.kind, symbol_flags, scope_id);
        let mut new_decls = vec![];

        let mut reference_builder = ReferenceBuilder::new(init, symbol_flags, scope_id, false, ctx);
        let remove_empty_object_pattern;

        // Add `_foo = foo()`
        if let Some(id) = reference_builder.binding.take() {
            let decl = ctx.ast.variable_declarator(
                SPAN,
                state.kind,
                id,
                NONE,
                Some(reference_builder.create_read_expression(ctx)),
                false,
            );
            new_decls.push(decl);
        }

        let mut temp_decls = vec![];
        let mut temp_keys = vec![];

        if let BindingPattern::ObjectPattern(pat) = &mut decl.id {
            // Example: `let { x, ...rest } = foo();`.
            remove_empty_object_pattern = pat.properties.is_empty();
            // Walk the properties that may contain a nested rest spread.
            temp_decls.extend(
                pat.properties
                    .iter_mut()
                    .flat_map(|p| self.recursive_walk_binding_pattern(&mut p.value, state, ctx)),
            );

            // Transform the object pattern with a rest pattern.
            if let Some(rest) = pat.rest.take() {
                let lhs = BindingPatternOrAssignmentTarget::BindingPattern(rest.unbox().argument);
                let mut all_primitives = true;
                // Create the access keys.
                // `let { a, b, ...c } = foo` -> `["a", "b"]`
                let keys = ctx.ast.vec_from_iter(pat.properties.iter_mut().filter_map(
                    |binding_property| {
                        Self::transform_property_key(
                            &mut binding_property.key,
                            &mut temp_keys,
                            &mut all_primitives,
                            state,
                            ctx,
                        )
                    },
                ));
                let datum = SpreadPair {
                    lhs,
                    keys,
                    has_no_properties: pat.properties.is_empty(),
                    all_primitives,
                };
                // Add `rest = babelHelpers.extends({}, (babelHelpers.objectDestructuringEmpty(_foo), _foo))`.
                // Or `rest = babelHelpers.objectWithoutProperties(_foo, ["x"])`.
                let (lhs, rhs) = datum.get_lhs_rhs(
                    &mut reference_builder,
                    &mut self.excluded_variable_declarators,
                    ctx,
                );
                if let BindingPatternOrAssignmentTarget::BindingPattern(lhs) = lhs {
                    let decl = ctx.ast.variable_declarator(
                        lhs.span(),
                        decl.kind,
                        lhs,
                        NONE,
                        Some(rhs),
                        false,
                    );
                    temp_decls.push(decl);
                }
            }
        } else {
            remove_empty_object_pattern = false;
            let data = self.recursive_walk_binding_pattern(&mut decl.id, state, ctx);
            temp_decls.extend(data);
        }

        new_decls.extend(temp_keys);

        // Insert the original declarator by copying its data out.
        if !remove_empty_object_pattern {
            let mut binding_pattern =
                ctx.ast.binding_pattern_object_pattern(decl.span, ctx.ast.vec(), NONE);
            mem::swap(&mut binding_pattern, &mut decl.id);
            let decl = ctx.ast.variable_declarator(
                decl.span,
                decl.kind,
                binding_pattern,
                NONE,
                Some(reference_builder.create_read_expression(ctx)),
                false,
            );
            new_decls.push(decl);
        }

        new_decls.extend(temp_decls);
        ctx.ast.vec_from_iter(new_decls)
    }

    // Returns all temporary references
    fn recursive_walk_binding_pattern(
        &mut self,
        pat: &mut BindingPattern<'a>,
        state: State,
        ctx: &mut TraverseCtx<'a>,
    ) -> Vec<VariableDeclarator<'a>> {
        match pat {
            BindingPattern::BindingIdentifier(_) => vec![],
            BindingPattern::ArrayPattern(array_pat) => array_pat
                .elements
                .iter_mut()
                .flatten()
                .flat_map(|p| self.recursive_walk_binding_pattern(p, state, ctx))
                .collect::<Vec<_>>(),
            BindingPattern::AssignmentPattern(assign_pat) => {
                self.recursive_walk_binding_pattern(&mut assign_pat.left, state, ctx)
            }
            BindingPattern::ObjectPattern(p) => {
                let data = p
                    .properties
                    .iter_mut()
                    .flat_map(|p| self.recursive_walk_binding_pattern(&mut p.value, state, ctx))
                    .collect::<Vec<_>>();
                if p.rest.is_some() {
                    let bound_identifier =
                        ctx.generate_uid("ref", state.scope_id, state.symbol_flags);
                    let id = mem::replace(pat, bound_identifier.create_binding_pattern(ctx));

                    let init = bound_identifier.create_read_expression(ctx);
                    let mut decl =
                        ctx.ast.variable_declarator(SPAN, state.kind, id, NONE, Some(init), false);
                    let mut decls = self
                        .transform_variable_declarator(&mut decl, ctx)
                        .into_iter()
                        .collect::<Vec<_>>();
                    decls.extend(data);
                    return decls;
                }
                data
            }
        }
    }

    // Create a reference for computed property keys.
    fn transform_property_key(
        key: &mut PropertyKey<'a>,
        new_decls: &mut Vec<VariableDeclarator<'a>>,
        all_primitives: &mut bool,
        state: State,
        ctx: &mut TraverseCtx<'a>,
    ) -> Option<ArrayExpressionElement<'a>> {
        match key {
            // `let { a, ... rest }`
            PropertyKey::StaticIdentifier(ident) => {
                let name = ident.name;
                let expr = ctx.ast.expression_string_literal(ident.span, name, None);
                Some(ArrayExpressionElement::from(expr))
            }
            // `let { 'a', ... rest }`
            // `let { ['a'], ... rest }`
            PropertyKey::StringLiteral(lit) => {
                let name = lit.value;
                let expr = ctx.ast.expression_string_literal(lit.span, name, None);
                Some(ArrayExpressionElement::from(expr))
            }
            // `let { [`a`], ... rest }`
            PropertyKey::TemplateLiteral(lit) if lit.is_no_substitution_template() => {
                let quasis = ctx.ast.vec1(lit.quasis[0].clone());
                let expressions = ctx.ast.vec();
                let expr = ctx.ast.expression_template_literal(lit.span, quasis, expressions);
                Some(ArrayExpressionElement::from(expr))
            }
            PropertyKey::PrivateIdentifier(_) => {
                /* syntax error */
                None
            }
            key => {
                let expr = key.as_expression_mut()?;
                // `let { [1], ... rest }`
                if expr.is_literal() {
                    let span = expr.span();
                    let s = expr.to_js_string(&WithoutGlobalReferenceInformation {}).unwrap();
                    let s = ctx.ast.str_from_cow(&s);
                    let expr = ctx.ast.expression_string_literal(span, s, None);
                    return Some(ArrayExpressionElement::from(expr));
                }
                *all_primitives = false;
                if let Expression::Identifier(ident) = expr {
                    let binding = MaybeBoundIdentifier::from_identifier_reference(ident, ctx);
                    if let Some(binding) = binding.to_bound_identifier() {
                        let expr = binding.create_read_expression(ctx);
                        return Some(ArrayExpressionElement::from(expr));
                    }
                }
                let bound_identifier =
                    ctx.generate_uid_based_on_node(expr, state.scope_id, state.symbol_flags);
                let p = bound_identifier.create_binding_pattern(ctx);
                let mut lhs = bound_identifier.create_read_expression(ctx);
                mem::swap(&mut lhs, expr);
                new_decls.push(ctx.ast.variable_declarator(
                    SPAN,
                    state.kind,
                    p,
                    NONE,
                    Some(lhs),
                    false,
                ));
                Some(ArrayExpressionElement::from(bound_identifier.create_read_expression(ctx)))
            }
        }
    }
}

#[derive(Debug, Clone, Copy)]
struct State {
    kind: VariableDeclarationKind,
    symbol_flags: SymbolFlags,
    scope_id: ScopeId,
}

impl State {
    fn new(kind: VariableDeclarationKind, symbol_flags: SymbolFlags, scope_id: ScopeId) -> Self {
        Self { kind, symbol_flags, scope_id }
    }
}

fn kind_to_symbol_flags(kind: VariableDeclarationKind) -> SymbolFlags {
    match kind {
        VariableDeclarationKind::Var => SymbolFlags::FunctionScopedVariable,
        VariableDeclarationKind::Let
        | VariableDeclarationKind::Using
        | VariableDeclarationKind::AwaitUsing => SymbolFlags::BlockScopedVariable,
        VariableDeclarationKind::Const => {
            SymbolFlags::BlockScopedVariable | SymbolFlags::ConstVariable
        }
    }
}

#[derive(Debug)]
enum BindingPatternOrAssignmentTarget<'a> {
    BindingPattern(BindingPattern<'a>),
    AssignmentTarget(AssignmentTarget<'a>),
}

#[derive(Debug)]
struct SpreadPair<'a> {
    lhs: BindingPatternOrAssignmentTarget<'a>,
    keys: ArenaVec<'a, ArrayExpressionElement<'a>>,
    has_no_properties: bool,
    all_primitives: bool,
}

impl<'a> SpreadPair<'a> {
    fn get_lhs_rhs(
        self,
        reference_builder: &mut ReferenceBuilder<'a>,
        excluded_variable_declarators: &mut Vec<VariableDeclarator<'a>>,
        ctx: &mut TraverseCtx<'a>,
    ) -> (BindingPatternOrAssignmentTarget<'a>, Expression<'a>) {
        let rhs = if self.has_no_properties {
            // The `ObjectDestructuringEmpty` function throws a type error when destructuring null.
            // `function _objectDestructuringEmpty(t) { if (null == t) throw new TypeError("Cannot destructure " + t); }`
            let mut arguments = ctx.ast.vec();
            // Add `{}`.
            arguments.push(Argument::ObjectExpression(
                ctx.ast.alloc_object_expression(SPAN, ctx.ast.vec()),
            ));
            // Add `(_objectDestructuringEmpty(b), b);`
            arguments.push(Argument::SequenceExpression(ctx.ast.alloc_sequence_expression(
                SPAN,
                {
                    let mut sequence = ctx.ast.vec();
                    sequence.push(helper_call_expr(
                        Helper::ObjectDestructuringEmpty,
                        ctx.ast.vec1(Argument::from(reference_builder.create_read_expression(ctx))),
                        ctx,
                    ));
                    sequence.push(reference_builder.create_read_expression(ctx));
                    sequence
                },
            )));
            helper_call_expr(Helper::Extends, arguments, ctx)
        } else {
            // / `let { a, b, ...c } = z` -> _objectWithoutProperties(_z, ["a", "b"]);
            // / `_objectWithoutProperties(_z, ["a", "b"])`
            let mut arguments =
                ctx.ast.vec1(Argument::from(reference_builder.create_read_expression(ctx)));
            let key_expression = ctx.ast.expression_array(SPAN, self.keys);

            let key_expression = if self.all_primitives
                && ctx.scoping.current_scope_id() != ctx.scoping().root_scope_id()
            {
                // Move the key_expression to the root scope.
                let bound_identifier = ctx.generate_uid_in_root_scope(
                    "excluded",
                    SymbolFlags::BlockScopedVariable | SymbolFlags::ConstVariable,
                );
                let kind = VariableDeclarationKind::Const;
                let declarator = ctx.ast.variable_declarator(
                    SPAN,
                    kind,
                    bound_identifier.create_binding_pattern(ctx),
                    NONE,
                    Some(key_expression),
                    false,
                );
                excluded_variable_declarators.push(declarator);
                bound_identifier.create_read_expression(ctx)
            } else if !self.all_primitives {
                // map to `toPropertyKey` to handle the possible non-string values
                // `[_ref].map(babelHelpers.toPropertyKey))`
                let property = ctx.ast.identifier_name(SPAN, "map");
                let callee = Expression::StaticMemberExpression(
                    ctx.ast.alloc_static_member_expression(SPAN, key_expression, property, false),
                );
                let arguments =
                    ctx.ast.vec1(Argument::from(helper_load(Helper::ToPropertyKey, ctx)));
                ctx.ast.expression_call(SPAN, callee, NONE, arguments, false)
            } else {
                key_expression
            };
            arguments.push(Argument::from(key_expression));
            helper_call_expr(Helper::ObjectWithoutProperties, arguments, ctx)
        };
        (self.lhs, rhs)
    }
}

#[derive(Debug)]
struct ReferenceBuilder<'a> {
    expr: Option<Expression<'a>>,
    binding: Option<BindingPattern<'a>>,
    maybe_bound_identifier: MaybeBoundIdentifier<'a>,
}

impl<'a> ReferenceBuilder<'a> {
    fn new(
        expr: &mut Expression<'a>,
        symbol_flags: SymbolFlags,
        scope_id: ScopeId,
        force_create_binding: bool,
        ctx: &mut TraverseCtx<'a>,
    ) -> Self {
        let expr = expr.take_in(ctx.ast);
        let binding;
        let maybe_bound_identifier;
        match &expr {
            Expression::Identifier(ident) if !force_create_binding => {
                binding = None;
                maybe_bound_identifier =
                    MaybeBoundIdentifier::from_identifier_reference(ident, ctx);
            }
            expr => {
                let bound_identifier = ctx.generate_uid_based_on_node(expr, scope_id, symbol_flags);
                binding = Some(bound_identifier.create_binding_pattern(ctx));
                maybe_bound_identifier = bound_identifier.to_maybe_bound_identifier();
            }
        }
        Self { expr: Some(expr), binding, maybe_bound_identifier }
    }

    fn create_read_expression(&mut self, ctx: &mut TraverseCtx<'a>) -> Expression<'a> {
        self.expr.take().unwrap_or_else(|| self.maybe_bound_identifier.create_read_expression(ctx))
    }
}