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exponentiation_operator.rs
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exponentiation_operator.rs
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//! ES2016: Exponentiation Operator
//!
//! This plugin transforms the exponentiation operator (`**`) to `Math.pow`.
//!
//! > This plugin is included in `preset-env`, in ES2016
//!
//! ## Example
//!
//! Input:
//! ```js
//! let x = 10 ** 2;
//! x **= 3;
//! obj.prop **= 4;
//! ```
//!
//! Output:
//! ```js
//! let x = Math.pow(10, 2);
//! x = Math.pow(x, 3);
//! obj["prop"] = Math.pow(obj["prop"], 4);
//! ```
//!
//! ## Implementation
//!
//! Implementation based on [@babel/plugin-transform-exponentiation-operator](https://babel.dev/docs/babel-plugin-transform-exponentiation-operator).
//!
//! ## References:
//!
//! * Babel plugin implementation:
//! <https://github.com/babel/babel/blob/main/packages/babel-plugin-transform-exponentiation-operator>
//! <https://github.com/babel/babel/tree/main/packages/babel-helper-builder-binary-assignment-operator-visitor>
//! * Exponentiation operator TC39 proposal: <https://github.com/tc39/proposal-exponentiation-operator>
//! * Exponentiation operator specification: <https://tc39.es/ecma262/#sec-exp-operator>
use oxc_allocator::{CloneIn, Vec};
use oxc_ast::{ast::*, NONE};
use oxc_semantic::{ReferenceFlags, SymbolFlags};
use oxc_span::SPAN;
use oxc_syntax::operator::{AssignmentOperator, BinaryOperator};
use oxc_traverse::{Ancestor, BoundIdentifier, Traverse, TraverseCtx};
use crate::TransformCtx;
pub struct ExponentiationOperator<'a, 'ctx> {
ctx: &'ctx TransformCtx<'a>,
}
impl<'a, 'ctx> ExponentiationOperator<'a, 'ctx> {
pub fn new(ctx: &'ctx TransformCtx<'a>) -> Self {
Self { ctx }
}
}
impl<'a, 'ctx> Traverse<'a> for ExponentiationOperator<'a, 'ctx> {
// Note: Do not transform to `Math.pow` with BigInt arguments - that's a runtime error
fn enter_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
match expr {
// `left ** right`
Expression::BinaryExpression(binary_expr) => {
if binary_expr.operator != BinaryOperator::Exponential
|| binary_expr.left.is_big_int_literal()
|| binary_expr.right.is_big_int_literal()
{
return;
}
Self::convert_binary_expression(expr, ctx);
}
// `left **= right`
Expression::AssignmentExpression(assign_expr) => {
if assign_expr.operator != AssignmentOperator::Exponential
|| assign_expr.right.is_big_int_literal()
{
return;
}
match &assign_expr.left {
AssignmentTarget::AssignmentTargetIdentifier(_) => {
self.convert_identifier_assignment(expr, ctx);
}
AssignmentTarget::StaticMemberExpression(_) => {
self.convert_static_member_expression_assignment(expr, ctx);
}
AssignmentTarget::ComputedMemberExpression(_) => {
self.convert_computed_member_expression_assignment(expr, ctx);
}
// Babel refuses to transform this: "We can't generate property ref for private name,
// please install `@babel/plugin-transform-class-properties`".
// But there's no reason not to.
AssignmentTarget::PrivateFieldExpression(_) => {
self.convert_private_field_assignment(expr, ctx);
}
_ => {}
}
}
_ => {}
}
}
}
impl<'a, 'ctx> ExponentiationOperator<'a, 'ctx> {
/// Convert `BinaryExpression`.
///
/// `left ** right` -> `Math.pow(left, right)`
//
// `#[inline]` so compiler knows `expr` is a `BinaryExpression`
#[inline]
fn convert_binary_expression(expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
let binary_expr = match ctx.ast.move_expression(expr) {
Expression::BinaryExpression(binary_expr) => binary_expr.unbox(),
_ => unreachable!(),
};
*expr = Self::math_pow(binary_expr.left, binary_expr.right, ctx);
}
/// Convert `AssignmentExpression` where assignee is an identifier.
///
/// `left **= right` transformed to:
/// * If `left` is a bound symbol:
/// -> `left = Math.pow(left, right)`
/// * If `left` is unbound:
/// -> `var _left; _left = left, left = Math.pow(_left, right)`
///
/// Temporary variable `_left` is to avoid side-effects of getting `left` from running twice.
//
// `#[inline]` so compiler knows `expr` is an `AssignmentExpression` with `IdentifierReference` on left
#[inline]
fn convert_identifier_assignment(
&mut self,
expr: &mut Expression<'a>,
ctx: &mut TraverseCtx<'a>,
) {
let Expression::AssignmentExpression(assign_expr) = expr else { unreachable!() };
let AssignmentTarget::AssignmentTargetIdentifier(ident) = &mut assign_expr.left else {
unreachable!()
};
let (pow_left, temp_var_inits) = self.get_pow_left_identifier(ident, ctx);
Self::convert_assignment(assign_expr, pow_left, ctx);
Self::revise_expression(expr, temp_var_inits, ctx);
}
/// Get left side of `Math.pow(pow_left, ...)` for identifier
fn get_pow_left_identifier(
&mut self,
ident: &mut IdentifierReference<'a>,
ctx: &mut TraverseCtx<'a>,
) -> (
// Left side of `Math.pow(pow_left, ...)`
Expression<'a>,
// Temporary var initializations
Vec<'a, Expression<'a>>,
) {
let mut temp_var_inits = ctx.ast.vec();
// Make sure side-effects of evaluating `left` only happen once
let reference = ctx.scoping.symbols_mut().get_reference_mut(ident.reference_id().unwrap());
let pow_left = if let Some(symbol_id) = reference.symbol_id() {
// This variable is declared in scope so evaluating it multiple times can't trigger a getter.
// No need for a temp var.
// `left **= right` is being transformed to `left = Math.pow(left, right)`,
// so if `left` is no longer being read from, update its `ReferenceFlags`.
if matches!(ctx.ancestry.parent(), Ancestor::ExpressionStatementExpression(_)) {
*reference.flags_mut() = ReferenceFlags::Write;
}
ctx.ast.expression_from_identifier_reference(ctx.create_bound_reference_id(
SPAN,
ident.name.clone(),
symbol_id,
ReferenceFlags::Read,
))
} else {
// Unbound reference. Could possibly trigger a getter so we need to only evaluate it once.
// Assign to a temp var.
let reference = ctx.ast.expression_from_identifier_reference(
ctx.create_unbound_reference_id(SPAN, ident.name.clone(), ReferenceFlags::Read),
);
let binding = self.create_temp_var(reference, &mut temp_var_inits, ctx);
binding.create_read_expression(ctx)
};
(pow_left, temp_var_inits)
}
/// Convert `AssignmentExpression` where assignee is a static member expression.
///
/// `obj.prop **= right` transformed to:
/// * If `obj` is a bound symbol:
/// -> `obj["prop"] = Math.pow(obj["prop"], right)`
/// * If `obj` is unbound:
/// -> `var _obj; _obj = obj, _obj["prop"] = Math.pow(_obj["prop"], right)`
///
/// `obj.foo.bar.qux **= right` transformed to:
/// ```js
/// var _obj$foo$bar;
/// _obj$foo$bar = obj.foo.bar, _obj$foo$bar["qux"] = Math.pow(_obj$foo$bar["qux"], right)
/// ```
///
/// Temporary variables are to avoid side-effects of getting `obj` / `obj.foo.bar` being run twice.
///
/// TODO(improve-on-babel): `obj.prop` does not need to be transformed to `obj["prop"]`.
//
// `#[inline]` so compiler knows `expr` is an `AssignmentExpression` with `StaticMemberExpression` on left
#[inline]
fn convert_static_member_expression_assignment(
&mut self,
expr: &mut Expression<'a>,
ctx: &mut TraverseCtx<'a>,
) {
let Expression::AssignmentExpression(assign_expr) = expr else { unreachable!() };
let AssignmentTarget::StaticMemberExpression(member_expr) = &mut assign_expr.left else {
unreachable!()
};
let (replacement_left, pow_left, temp_var_inits) =
self.get_pow_left_static_member(member_expr, ctx);
assign_expr.left = replacement_left;
Self::convert_assignment(assign_expr, pow_left, ctx);
Self::revise_expression(expr, temp_var_inits, ctx);
}
/// Get left side of `Math.pow(pow_left, ...)` for static member expression
/// and replacement for left side of assignment.
fn get_pow_left_static_member(
&mut self,
member_expr: &mut StaticMemberExpression<'a>,
ctx: &mut TraverseCtx<'a>,
) -> (
// Replacement left of assignment
AssignmentTarget<'a>,
// Left side of `Math.pow(pow_left, ...)`
Expression<'a>,
// Temporary var initializations
Vec<'a, Expression<'a>>,
) {
// Object part of 2nd member expression
// ```
// obj["prop"] = Math.pow(obj["prop"], right)
// ^^^
// ```
let mut temp_var_inits = ctx.ast.vec();
let obj = self.get_second_member_expression_object(
&mut member_expr.object,
&mut temp_var_inits,
ctx,
);
// Property part of 2nd member expression
// ```
// obj["prop"] = Math.pow(obj["prop"], right)
// ^^^^^^
// ```
let prop_span = member_expr.property.span;
let prop_name = member_expr.property.name.clone();
let prop = ctx.ast.expression_string_literal(prop_span, prop_name.clone());
// Complete 2nd member expression
// ```
// obj["prop"] = Math.pow(obj["prop"], right)
// ^^^^^^^^^^^
// ```
let pow_left = Expression::from(ctx.ast.member_expression_computed(SPAN, obj, prop, false));
// Replacement for original member expression
// ```
// obj["prop"] = Math.pow(obj["prop"], right)
// ^^^^^^^^^^^
// ```
let replacement_left =
AssignmentTarget::ComputedMemberExpression(ctx.ast.alloc_computed_member_expression(
member_expr.span,
ctx.ast.move_expression(&mut member_expr.object),
ctx.ast.expression_string_literal(prop_span, prop_name),
false,
));
(replacement_left, pow_left, temp_var_inits)
}
/// Convert `AssignmentExpression` where assignee is a computed member expression.
///
/// `obj[prop] **= right` transformed to:
/// * If `obj` is a bound symbol:
/// -> `var _prop; _prop = prop, obj[_prop] = Math.pow(obj[_prop], 2)`
/// * If `obj` is unbound:
/// -> `var _obj, _prop; _obj = obj, _prop = prop, _obj[_prop] = Math.pow(_obj[_prop], 2)`
///
/// `obj.foo.bar[qux] **= right` transformed to:
/// ```js
/// var _obj$foo$bar, _qux;
/// _obj$foo$bar = obj.foo.bar, _qux = qux, _obj$foo$bar[_qux] = Math.pow(_obj$foo$bar[_qux], right)
/// ```
///
/// Temporary variables are to avoid side-effects of getting `obj` / `obj.foo.bar` or `prop` being run twice.
///
/// TODO(improve-on-babel):
/// 1. If `prop` is bound, it doesn't need a temp variable `_prop`.
/// 2. Temp var initializations could be inlined:
/// * Current: `(_obj = obj, _prop = prop, _obj[_prop] = Math.pow(_obj[_prop], 2))`
/// * Could be: `(_obj = obj)[_prop = prop] = Math.pow(_obj[_prop], 2)`
//
// `#[inline]` so compiler knows `expr` is an `AssignmentExpression` with `ComputedMemberExpression` on left
#[inline]
fn convert_computed_member_expression_assignment(
&mut self,
expr: &mut Expression<'a>,
ctx: &mut TraverseCtx<'a>,
) {
let Expression::AssignmentExpression(assign_expr) = expr else { unreachable!() };
let AssignmentTarget::ComputedMemberExpression(member_expr) = &mut assign_expr.left else {
unreachable!()
};
let (pow_left, temp_var_inits) = self.get_pow_left_computed_member(member_expr, ctx);
Self::convert_assignment(assign_expr, pow_left, ctx);
Self::revise_expression(expr, temp_var_inits, ctx);
}
/// Get left side of `Math.pow(pow_left, ...)` for computed member expression
fn get_pow_left_computed_member(
&mut self,
member_expr: &mut ComputedMemberExpression<'a>,
ctx: &mut TraverseCtx<'a>,
) -> (
// Left side of `Math.pow(pow_left, ...)`
Expression<'a>,
// Temporary var initializations
Vec<'a, Expression<'a>>,
) {
// Object part of 2nd member expression
// ```
// obj[_prop] = Math.pow(obj[_prop], right)
// ^^^
// ```
let mut temp_var_inits = ctx.ast.vec();
let obj = self.get_second_member_expression_object(
&mut member_expr.object,
&mut temp_var_inits,
ctx,
);
// Property part of 2nd member expression
// ```
// obj[_prop] = Math.pow(obj[_prop], right)
// ^^^^^ replaced ^^^^^ prop
// ```
let prop = &mut member_expr.expression;
let prop = if prop.is_literal() {
prop.clone_in(ctx.ast.allocator)
} else {
let owned_prop = ctx.ast.move_expression(prop);
let binding = self.create_temp_var(owned_prop, &mut temp_var_inits, ctx);
*prop = binding.create_read_expression(ctx);
binding.create_read_expression(ctx)
};
// Complete 2nd member expression
// ```
// obj[_prop] = Math.pow(obj[_prop], right)
// ^^^^^^^^^^
// ```
let pow_left = Expression::from(ctx.ast.member_expression_computed(SPAN, obj, prop, false));
(pow_left, temp_var_inits)
}
/// Convert `AssignmentExpression` where assignee is a private field member expression.
///
/// `obj.#prop **= right` transformed to:
/// * If `obj` is a bound symbol:
/// -> `obj.#prop = Math.pow(obj.#prop, right)`
/// * If `obj` is unbound:
/// -> `var _obj; _obj = obj, _obj.#prop = Math.pow(_obj.#prop, right)`
///
/// `obj.foo.bar.#qux **= right` transformed to:
/// ```js
/// var _obj$foo$bar;
/// _obj$foo$bar = obj.foo.bar, _obj$foo$bar.#qux = Math.pow(_obj$foo$bar.#qux, right)
/// ```
///
/// Temporary variable is to avoid side-effects of getting `obj` / `obj.foo.bar` being run twice.
//
// `#[inline]` so compiler knows `expr` is an `AssignmentExpression` with `PrivateFieldExpression` on left
#[inline]
fn convert_private_field_assignment(
&mut self,
expr: &mut Expression<'a>,
ctx: &mut TraverseCtx<'a>,
) {
let Expression::AssignmentExpression(assign_expr) = expr else { unreachable!() };
let AssignmentTarget::PrivateFieldExpression(member_expr) = &mut assign_expr.left else {
unreachable!()
};
let (pow_left, temp_var_inits) = self.get_pow_left_private_field(member_expr, ctx);
Self::convert_assignment(assign_expr, pow_left, ctx);
Self::revise_expression(expr, temp_var_inits, ctx);
}
/// Get left side of `Math.pow(pow_left, ...)` for static member expression
/// and replacement for left side of assignment.
fn get_pow_left_private_field(
&mut self,
field_expr: &mut PrivateFieldExpression<'a>,
ctx: &mut TraverseCtx<'a>,
) -> (
// Left side of `Math.pow(pow_left, ...)`
Expression<'a>,
// Temporary var initializations
Vec<'a, Expression<'a>>,
) {
// Object part of 2nd member expression
// ```
// obj.#prop = Math.pow(obj.#prop, right)
// ^^^
// ```
let mut temp_var_inits = ctx.ast.vec();
let obj = self.get_second_member_expression_object(
&mut field_expr.object,
&mut temp_var_inits,
ctx,
);
// Property part of 2nd member expression
// ```
// obj.#prop = Math.pow(obj.#prop, right)
// ^^^^^
// ```
let field = field_expr.field.clone_in(ctx.ast.allocator);
// Complete 2nd member expression
// ```
// obj.#prop = Math.pow(obj.#prop, right)
// ^^^^^^^^^
// ```
let pow_left = Expression::from(
ctx.ast.member_expression_private_field_expression(SPAN, obj, field, false),
);
(pow_left, temp_var_inits)
}
/// Get object part of 2nd member expression to be used as `left` in `Math.pow(left, right)`.
///
/// Also update the original `obj` passed in to function, and add a temp var initializer, if necessary.
///
/// Original:
/// ```js
/// obj.prop **= 2`
/// ^^^ original `obj` passed in to this function
/// ```
///
/// is transformed to:
///
/// If `obj` is a bound symbol:
/// ```js
/// obj["prop"] = Math.pow(obj["prop"], 2)
/// ^^^ not updated ^^^ returned
/// ```
///
/// If `obj` is unbound:
/// ```js
/// var _obj;
/// _obj = obj, _obj["prop"] = Math.pow(_obj["prop"], 2)
/// ^^^^ updated ^^^^ returned
/// ^^^^^^^^^^ added to `temp_var_inits`
/// ```
///
/// Original:
/// ```js
/// obj.foo.bar.qux **= 2
/// ^^^^^^^^^^^ original `obj` passed in to this function
/// ```
/// is transformed to:
/// ```js
/// var _obj$foo$bar;
/// _obj$foo$bar = obj.foo.bar, _obj$foo$bar["qux"] = Math.pow(_obj$foo$bar["qux"], 2)
/// ^^^^^^^^^^^^ updated ^^^^^^^^^^^^ returned
/// ^^^^^^^^^^^^^^^^^^^^^^^^^^ added to `temp_var_inits`
/// ```
fn get_second_member_expression_object(
&mut self,
obj: &mut Expression<'a>,
temp_var_inits: &mut Vec<'a, Expression<'a>>,
ctx: &mut TraverseCtx<'a>,
) -> Expression<'a> {
// If the object reference that we need to save is locally declared, evaluating it multiple times
// will not trigger getters or setters. `super` cannot be directly assigned, so use it directly too.
// TODO(improve-on-babel): We could also skip creating a temp var for `this.x **= 2`.
match obj {
Expression::Super(super_) => return ctx.ast.expression_super(super_.span),
Expression::Identifier(ident) => {
let symbol_id =
ctx.symbols().get_reference(ident.reference_id().unwrap()).symbol_id();
if let Some(symbol_id) = symbol_id {
// This variable is declared in scope so evaluating it multiple times can't trigger a getter.
// No need for a temp var.
return ctx.ast.expression_from_identifier_reference(
ctx.create_bound_reference_id(
SPAN,
ident.name.clone(),
symbol_id,
ReferenceFlags::Read,
),
);
}
// Unbound reference. Could possibly trigger a getter so we need to only evaluate it once.
// Assign to a temp var.
}
_ => {
// Other expression. Assign to a temp var.
}
}
let binding = self.create_temp_var(ctx.ast.move_expression(obj), temp_var_inits, ctx);
*obj = binding.create_read_expression(ctx);
binding.create_read_expression(ctx)
}
/// `x **= right` -> `x = Math.pow(pow_left, right)` (with provided `pow_left`)
fn convert_assignment(
assign_expr: &mut AssignmentExpression<'a>,
pow_left: Expression<'a>,
ctx: &mut TraverseCtx<'a>,
) {
let pow_right = ctx.ast.move_expression(&mut assign_expr.right);
assign_expr.right = Self::math_pow(pow_left, pow_right, ctx);
assign_expr.operator = AssignmentOperator::Assign;
}
/// If needs temp var initializers, replace expression `expr` with `(temp1, temp2, expr)`.
fn revise_expression(
expr: &mut Expression<'a>,
mut temp_var_inits: Vec<'a, Expression<'a>>,
ctx: &mut TraverseCtx<'a>,
) {
if !temp_var_inits.is_empty() {
temp_var_inits.reserve_exact(1);
temp_var_inits.push(ctx.ast.move_expression(expr));
*expr = ctx.ast.expression_sequence(SPAN, temp_var_inits);
}
}
/// `Math.pow(left, right)`
fn math_pow(
left: Expression<'a>,
right: Expression<'a>,
ctx: &mut TraverseCtx<'a>,
) -> Expression<'a> {
let math_symbol_id = ctx.scopes().find_binding(ctx.current_scope_id(), "Math");
let ident_math =
ctx.create_reference_id(SPAN, Atom::from("Math"), math_symbol_id, ReferenceFlags::Read);
let object = ctx.ast.expression_from_identifier_reference(ident_math);
let property = ctx.ast.identifier_name(SPAN, "pow");
let callee =
Expression::from(ctx.ast.member_expression_static(SPAN, object, property, false));
let arguments = ctx.ast.vec_from_iter([Argument::from(left), Argument::from(right)]);
ctx.ast.expression_call(SPAN, callee, NONE, arguments, false)
}
/// Create a temporary variable.
/// Add a `var _name;` statement to enclosing scope.
/// Add initialization expression `_name = expr` to `temp_var_inits`.
/// Return `BoundIdentifier` for the temp var.
fn create_temp_var(
&mut self,
expr: Expression<'a>,
temp_var_inits: &mut Vec<'a, Expression<'a>>,
ctx: &mut TraverseCtx<'a>,
) -> BoundIdentifier<'a> {
let binding = ctx.generate_uid_in_current_scope_based_on_node(
&expr,
SymbolFlags::FunctionScopedVariable,
);
// var _name;
self.ctx.var_declarations.insert(&binding, None, ctx);
// Add new reference `_name = name` to `temp_var_inits`
temp_var_inits.push(ctx.ast.expression_assignment(
SPAN,
AssignmentOperator::Assign,
binding.create_read_write_target(ctx),
expr,
));
binding
}
}