feat(transformer): support exponentiation operator plugin (#4876)

The implementation copy from the original implementation which removed in https://github.com/oxc-project/oxc/pull/2865.

crates/oxc_transformer/src/es2016/exponentiation_operator.rs

@@ -0,0 +1,322 @@
+use std::cell::Cell;
+
+use oxc_allocator::{CloneIn, Vec};
+use oxc_ast::ast::*;
+use oxc_semantic::{ReferenceFlag, SymbolFlags};
+use oxc_span::SPAN;
+use oxc_syntax::operator::{AssignmentOperator, BinaryOperator};
+use oxc_traverse::TraverseCtx;
+
+use crate::context::Ctx;
+
+/// ES2016: Exponentiation Operator
+///
+/// References:
+/// * <https://babel.dev/docs/babel-plugin-transform-exponentiation-operator>
+/// * <https://github.com/babel/babel/blob/main/packages/babel-plugin-transform-exponentiation-operator>
+/// * <https://github.com/babel/babel/blob/main/packages/babel-helper-builder-binary-assignment-operator-visitor>
+pub struct ExponentiationOperator<'a> {
+    _ctx: Ctx<'a>,
+    var_declarations: std::vec::Vec<Vec<'a, VariableDeclarator<'a>>>,
+}
+
+#[derive(Debug)]
+struct Exploded<'a> {
+    reference: AssignmentTarget<'a>,
+    uid: Expression<'a>,
+}
+
+impl<'a> ExponentiationOperator<'a> {
+    pub fn new(ctx: Ctx<'a>) -> Self {
+        Self { _ctx: ctx, var_declarations: vec![] }
+    }
+
+    fn clone_identifier_reference(
+        ident: &IdentifierReference<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> IdentifierReference<'a> {
+        let reference = ctx.symbols().get_reference(ident.reference_id.get().unwrap());
+        let symbol_id = reference.symbol_id();
+        let flag = reference.flag();
+        ctx.create_reference_id(ident.span, ident.name.clone(), symbol_id, *flag)
+    }
+
+    fn clone_expression(expr: &Expression<'a>, ctx: &mut TraverseCtx<'a>) -> Expression<'a> {
+        match expr {
+            Expression::Identifier(ident) => ctx
+                .ast
+                .expression_from_identifier_reference(Self::clone_identifier_reference(ident, ctx)),
+            _ => expr.clone_in(ctx.ast.allocator),
+        }
+    }
+
+    pub fn transform_statements(
+        &mut self,
+        _statements: &mut Vec<'a, Statement<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        self.var_declarations.push(ctx.ast.vec());
+    }
+
+    pub fn transform_statements_on_exit(
+        &mut self,
+        statements: &mut Vec<'a, Statement<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        if let Some(declarations) = self.var_declarations.pop() {
+            if declarations.is_empty() {
+                return;
+            }
+            let variable = ctx.ast.alloc_variable_declaration(
+                SPAN,
+                VariableDeclarationKind::Var,
+                declarations,
+                false,
+            );
+            statements.insert(0, Statement::VariableDeclaration(variable));
+        }
+    }
+
+    pub fn transform_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
+        // left ** right
+        if let Expression::BinaryExpression(binary_expr) = expr {
+            if binary_expr.operator == BinaryOperator::Exponential {
+                let left = ctx.ast.move_expression(&mut binary_expr.left);
+                let right = ctx.ast.move_expression(&mut binary_expr.right);
+                *expr = Self::math_pow(left, right, ctx);
+            }
+        }
+
+        // left **= right
+        if let Expression::AssignmentExpression(assign_expr) = expr {
+            if assign_expr.operator == AssignmentOperator::Exponential {
+                let mut nodes = ctx.ast.vec();
+                let Some(Exploded { reference, uid }) =
+                    self.explode(&mut assign_expr.left, &mut nodes, ctx)
+                else {
+                    return;
+                };
+                let right = ctx.ast.move_expression(&mut assign_expr.right);
+                let right = Self::math_pow(uid, right, ctx);
+                let assign_expr = ctx.ast.expression_assignment(
+                    SPAN,
+                    AssignmentOperator::Assign,
+                    reference,
+                    right,
+                );
+                nodes.push(assign_expr);
+                *expr = ctx.ast.expression_sequence(SPAN, nodes);
+            }
+        }
+    }
+
+    /// `left ** right` -> `Math.pow(left, right)`
+    fn math_pow(
+        left: Expression<'a>,
+        right: Expression<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Expression<'a> {
+        let ident_math =
+            ctx.create_reference_id(SPAN, ctx.ast.atom("Math"), None, ReferenceFlag::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 mut arguments = ctx.ast.vec_with_capacity(2);
+        arguments.push(Argument::from(left));
+        arguments.push(Argument::from(right));
+        ctx.ast.expression_call(
+            SPAN,
+            arguments,
+            callee,
+            None::<TSTypeParameterInstantiation<'_>>,
+            false,
+        )
+    }
+
+    /// Change `lhs **= 2` to `var temp; temp = lhs, lhs = Math.pow(temp, 2);`.
+    /// If the lhs is a member expression `obj.ref` or `obj[ref]`, assign them to a temporary variable so side-effects are not computed twice.
+    /// For `obj.ref`, change it to `var _obj; _obj = obj, _obj["ref"] = Math.pow(_obj["ref"], 2)`.
+    /// For `obj[ref]`, change it to `var _obj, _ref; _obj = obj, _ref = ref, _obj[_ref] = Math.pow(_obj[_ref], 2);`.
+    fn explode(
+        &mut self,
+        node: &mut AssignmentTarget<'a>,
+        nodes: &mut Vec<'a, Expression<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Option<Exploded<'a>> {
+        let node = node.as_simple_assignment_target_mut()?;
+        let obj = self.get_obj_ref(node, nodes, ctx)?;
+        let (reference, uid) = match node {
+            SimpleAssignmentTarget::AssignmentTargetIdentifier(ident) => {
+                let reference = AssignmentTarget::AssignmentTargetIdentifier(
+                    ctx.ast.alloc(Self::clone_identifier_reference(ident.as_ref(), ctx)),
+                );
+                (reference, obj)
+            }
+            match_member_expression!(SimpleAssignmentTarget) => {
+                let member_expr = node.to_member_expression_mut();
+                let computed = member_expr.is_computed();
+                let prop = self.get_prop_ref(member_expr, nodes, ctx)?;
+                let optional = false;
+                let obj_clone = Self::clone_expression(&obj, ctx);
+                let (reference, uid) = match &prop {
+                    Expression::Identifier(ident) if !computed => {
+                        let ident = IdentifierName::new(SPAN, ident.name.clone());
+                        (
+                            // TODO:
+                            // Both of these are the same, but it's in order to avoid after cloning without reference_id.
+                            // Related: https://github.com/oxc-project/oxc/issues/4804
+                            ctx.ast.member_expression_static(
+                                SPAN,
+                                obj_clone,
+                                ident.clone(),
+                                optional,
+                            ),
+                            ctx.ast.member_expression_static(SPAN, obj, ident, optional),
+                        )
+                    }
+                    _ => {
+                        let prop_clone = Self::clone_expression(&prop, ctx);
+                        (
+                            ctx.ast
+                                .member_expression_computed(SPAN, obj_clone, prop_clone, optional),
+                            ctx.ast.member_expression_computed(SPAN, obj, prop, optional),
+                        )
+                    }
+                };
+                (
+                    AssignmentTarget::from(
+                        ctx.ast.simple_assignment_target_member_expression(reference),
+                    ),
+                    Expression::from(uid),
+                )
+            }
+            _ => return None,
+        };
+        Some(Exploded { reference, uid })
+    }
+
+    /// Make sure side-effects of evaluating `obj` of `obj.ref` and `obj[ref]` only happen once.
+    fn get_obj_ref(
+        &mut self,
+        node: &mut SimpleAssignmentTarget<'a>,
+        nodes: &mut Vec<'a, Expression<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Option<Expression<'a>> {
+        let reference = match node {
+            SimpleAssignmentTarget::AssignmentTargetIdentifier(ident) => {
+                if ident
+                    .reference_id
+                    .get()
+                    .is_some_and(|reference_id| ctx.symbols().has_binding(reference_id))
+                {
+                    // this variable is declared in scope so we can be 100% sure
+                    // that evaluating it multiple times won't trigger a getter
+                    // or something else
+                    return Some(ctx.ast.expression_from_identifier_reference(
+                        Self::clone_identifier_reference(ident, ctx),
+                    ));
+                }
+                // could possibly trigger a getter so we need to only evaluate it once
+                ctx.ast.expression_from_identifier_reference(Self::clone_identifier_reference(
+                    ident, ctx,
+                ))
+            }
+            match_member_expression!(SimpleAssignmentTarget) => {
+                let expr = match node {
+                    SimpleAssignmentTarget::ComputedMemberExpression(e) => &mut e.object,
+                    SimpleAssignmentTarget::StaticMemberExpression(e) => &mut e.object,
+                    SimpleAssignmentTarget::PrivateFieldExpression(e) => &mut e.object,
+                    _ => unreachable!(),
+                };
+                let expr = ctx.ast.move_expression(expr);
+                // the object reference that we need to save is locally declared
+                // so as per the previous comment we can be 100% sure evaluating
+                // it multiple times will be safe
+                // Super cannot be directly assigned so lets return it also
+                if matches!(expr, Expression::Super(_))
+                    || matches!(&expr, Expression::Identifier(ident) if ident
+                        .reference_id
+                        .get()
+                        .is_some_and(|reference_id| ctx.symbols().has_binding(reference_id)))
+                {
+                    return Some(expr);
+                }
+
+                expr
+            }
+            _ => return None,
+        };
+        Some(self.add_new_reference(reference, nodes, ctx))
+    }
+
+    /// Make sure side-effects of evaluating `ref` of `obj.ref` and `obj[ref]` only happen once.
+    fn get_prop_ref(
+        &mut self,
+        node: &mut MemberExpression<'a>,
+        nodes: &mut Vec<'a, Expression<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Option<Expression<'a>> {
+        let expr = match node {
+            MemberExpression::ComputedMemberExpression(expr) => {
+                let expr = ctx.ast.move_expression(&mut expr.expression);
+                if expr.is_literal() {
+                    return Some(expr);
+                }
+                expr
+            }
+            MemberExpression::StaticMemberExpression(expr) => {
+                return Some(ctx.ast.expression_string_literal(SPAN, expr.property.name.clone()));
+            }
+            MemberExpression::PrivateFieldExpression(_) => {
+                // From babel: "We can't generate property ref for private name, please install `@babel/plugin-transform-class-properties`"
+                return None;
+            }
+        };
+        Some(self.add_new_reference(expr, nodes, ctx))
+    }
+
+    fn add_new_reference(
+        &mut self,
+        expr: Expression<'a>,
+        nodes: &mut Vec<'a, Expression<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Expression<'a> {
+        let name = match expr {
+            Expression::Identifier(ref ident) => ident.name.clone().as_str(),
+            _ => "ref",
+        };
+
+        let symbol_id =
+            ctx.generate_uid_in_current_scope(name, SymbolFlags::FunctionScopedVariable);
+        let symbol_name = ctx.ast.atom(ctx.symbols().get_name(symbol_id));
+
+        {
+            // var _name;
+            let binding_identifier = BindingIdentifier {
+                span: SPAN,
+                name: symbol_name.clone(),
+                symbol_id: Cell::new(Some(symbol_id)),
+            };
+            let kind = VariableDeclarationKind::Var;
+            let id = ctx.ast.binding_pattern_kind_from_binding_identifier(binding_identifier);
+            let id = ctx.ast.binding_pattern(id, None::<TSTypeAnnotation<'_>>, false);
+            self.var_declarations
+                .last_mut()
+                .unwrap()
+                .push(ctx.ast.variable_declarator(SPAN, kind, id, None, false));
+        }
+
+        let ident =
+            ctx.create_reference_id(SPAN, symbol_name, Some(symbol_id), ReferenceFlag::Read);
+
+        // let ident = self.create_new_var_with_expression(&expr);
+        // Add new reference `_name = name` to nodes
+        let left = ctx.ast.simple_assignment_target_from_identifier_reference(
+            Self::clone_identifier_reference(&ident, ctx),
+        );
+        let op = AssignmentOperator::Assign;
+        nodes.push(ctx.ast.expression_assignment(SPAN, op, AssignmentTarget::from(left), expr));
+        ctx.ast.expression_from_identifier_reference(ident)
+    }
+}

crates/oxc_transformer/src/es2016/mod.rs

@@ -0,0 +1,52 @@
+mod exponentiation_operator;
+mod options;
+
+pub use exponentiation_operator::ExponentiationOperator;
+pub use options::ES2016Options;
+use oxc_allocator::Vec;
+use oxc_ast::ast::*;
+use oxc_traverse::TraverseCtx;
+use std::rc::Rc;
+
+use crate::context::Ctx;
+
+#[allow(dead_code)]
+pub struct ES2016<'a> {
+    ctx: Ctx<'a>,
+    options: ES2016Options,
+
+    // Plugins
+    exponentiation_operator: ExponentiationOperator<'a>,
+}
+
+impl<'a> ES2016<'a> {
+    pub fn new(options: ES2016Options, ctx: Ctx<'a>) -> Self {
+        Self { exponentiation_operator: ExponentiationOperator::new(Rc::clone(&ctx)), ctx, options }
+    }
+
+    pub fn transform_statements(
+        &mut self,
+        statements: &mut Vec<'a, Statement<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        if self.options.exponentiation_operator {
+            self.exponentiation_operator.transform_statements(statements, ctx);
+        }
+    }
+
+    pub fn transform_statements_on_exit(
+        &mut self,
+        statements: &mut Vec<'a, Statement<'a>>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        if self.options.exponentiation_operator {
+            self.exponentiation_operator.transform_statements_on_exit(statements, ctx);
+        }
+    }
+
+    pub fn transform_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
+        if self.options.exponentiation_operator {
+            self.exponentiation_operator.transform_expression(expr, ctx);
+        }
+    }
+}

crates/oxc_transformer/src/es2016/options.rs

@@ -0,0 +1,16 @@
+use serde::Deserialize;
+
+#[derive(Debug, Default, Clone, Deserialize)]
+#[serde(default, rename_all = "camelCase", deny_unknown_fields)]
+pub struct ES2016Options {
+    #[serde(skip)]
+    pub exponentiation_operator: bool,
+}
+
+impl ES2016Options {
+    #[must_use]
+    pub fn with_exponentiation_operator(mut self, enable: bool) -> Self {
+        self.exponentiation_operator = enable;
+        self
+    }
+}

crates/oxc_transformer/src/lib.rs

@@ -15,6 +15,7 @@ mod options;
 // Presets: <https://babel.dev/docs/presets>
 mod env;
 mod es2015;
+mod es2016;
 mod react;
 mod typescript;
 
@@ -25,6 +26,7 @@ mod helpers {
 
 use std::{path::Path, rc::Rc};
 
+use es2016::ES2016;
 use oxc_allocator::{Allocator, Vec};
 use oxc_ast::{ast::*, AstBuilder, Trivias};
 use oxc_diagnostics::OxcDiagnostic;
@@ -58,6 +60,7 @@ pub struct Transformer<'a> {
     // NOTE: all callbacks must run in order.
     x0_typescript: TypeScript<'a>,
     x1_react: React<'a>,
+    x2_es2016: ES2016<'a>,
     x3_es2015: ES2015<'a>,
 }
 
@@ -82,6 +85,7 @@ impl<'a> Transformer<'a> {
             ctx: Rc::clone(&ctx),
             x0_typescript: TypeScript::new(options.typescript, Rc::clone(&ctx)),
             x1_react: React::new(options.react, Rc::clone(&ctx)),
+            x2_es2016: ES2016::new(options.es2016, Rc::clone(&ctx)),
             x3_es2015: ES2015::new(options.es2015, ctx),
         }
     }
@@ -160,6 +164,7 @@ impl<'a> Traverse<'a> for Transformer<'a> {
     fn enter_expression(&mut self, expr: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
         self.x0_typescript.transform_expression(expr);
         self.x1_react.transform_expression(expr, ctx);
+        self.x2_es2016.transform_expression(expr, ctx);
         self.x3_es2015.transform_expression(expr);
     }
 
@@ -244,13 +249,15 @@ impl<'a> Traverse<'a> for Transformer<'a> {
         self.x0_typescript.transform_property_definition(def);
     }
 
-    fn enter_statements(&mut self, stmts: &mut Vec<'a, Statement<'a>>, _ctx: &mut TraverseCtx<'a>) {
+    fn enter_statements(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: &mut TraverseCtx<'a>) {
         self.x0_typescript.transform_statements(stmts);
+        self.x2_es2016.transform_statements(stmts, ctx);
         self.x3_es2015.enter_statements(stmts);
     }
 
     fn exit_statements(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: &mut TraverseCtx<'a>) {
         self.x0_typescript.transform_statements_on_exit(stmts, ctx);
+        self.x2_es2016.transform_statements_on_exit(stmts, ctx);
         self.x3_es2015.exit_statements(stmts);
     }
 

crates/oxc_transformer/src/options/transformer.rs

@@ -7,6 +7,7 @@ use crate::{
     compiler_assumptions::CompilerAssumptions,
     env::{can_enable_plugin, EnvOptions, Versions},
     es2015::{ArrowFunctionsOptions, ES2015Options},
+    es2016::ES2016Options,
     options::babel::BabelOptions,
     react::ReactOptions,
     typescript::TypeScriptOptions,
@@ -34,6 +35,8 @@ pub struct TransformOptions {
     pub react: ReactOptions,
 
     pub es2015: ES2015Options,
+
+    pub es2016: ES2016Options,
 }
 
 impl TransformOptions {
@@ -104,6 +107,11 @@ impl TransformOptions {
             })
         });
 
+        let es2016 = ES2016Options::default().with_exponentiation_operator({
+            let plugin_name = "transform-exponentiation-operator";
+            enable_plugin(plugin_name, options, &env_options, &targets).is_some()
+        });
+
         let typescript = {
             let plugin_name = "transform-typescript";
             from_value::<TypeScriptOptions>(get_plugin_options(plugin_name, options))
@@ -135,6 +143,7 @@ impl TransformOptions {
             typescript,
             react,
             es2015,
+            es2016,
         })
     }
 }

tasks/transform_conformance/babel.snap.md

@@ -1,6 +1,6 @@
 commit: 12619ffe
 
-Passed: 453/927
+Passed: 456/931
 
 # All Passed:
 * babel-preset-react
@@ -433,6 +433,9 @@ Passed: 453/927
 * shipped-proposals/new-class-features-chrome-94/input.js
 * shipped-proposals/new-class-features-firefox-70/input.js
 
+# babel-plugin-transform-exponentiation-operator (3/4)
+* regression/4349/input.js
+
 # babel-plugin-transform-arrow-functions (1/6)
 * assumption-newableArrowFunctions-false/basic/input.js
 * assumption-newableArrowFunctions-false/naming/input.js

tasks/transform_conformance/babel_exec.snap.md

@@ -1,8 +1,9 @@
 commit: 12619ffe
 
-Passed: 8/14
+Passed: 10/16
 
 # All Passed:
+* babel-plugin-transform-exponentiation-operator
 * babel-plugin-transform-arrow-functions
 
 

tasks/transform_conformance/src/constants.rs

@@ -30,8 +30,8 @@ pub(crate) const PLUGINS: &[&str] = &[
     // // [Regex] "babel-plugin-transform-named-capturing-groups-regex",
     // // ES2017
     // "babel-plugin-transform-async-to-generator",
-    // // ES2016
-    // "babel-plugin-transform-exponentiation-operator",
+    // ES2016
+    "babel-plugin-transform-exponentiation-operator",
     // // ES2015
     "babel-plugin-transform-arrow-functions",
     // "babel-plugin-transform-function-name",