feat(transform): support es2015 new target (#1967)

Here implementing the es2015 new target transform, see detail at
https://babel.dev/docs/babel-plugin-transform-template-new-target.

Here has three kinds need to be distinguished.

- `NewTargetKind::Method`, it from `AstKind::ObjectMethod` or
`AstKind::MethodDefinitionKind::Get/Set/Method`. It will be transformed
to `void 0`.
- `NewTargetKind::Constructor`, is from `
AstKind::MethodDefinitionKind::Constructor`. It will be transformed to
`this.constructor`.
- `NewTargetKind::Function`, is from ` AstKind::Function`, here the
function is not the above function. It will be transformed to `this
instanceof _target ? this.constructor : void 0`, here `_target` comes
from the function name or is created by scope uid ident.

crates/oxc_semantic/src/scope.rs

@@ -183,8 +183,13 @@ impl ScopeTree {
         expr.gather(&mut |part| parts.push(part));
         let name = parts.join("$");
         let name = name.trim_start_matches('_');
+        self.generate_uid(name)
+    }
+
+    // <https://github.com/babel/babel/blob/419644f27c5c59deb19e71aaabd417a3bc5483ca/packages/babel-traverse/src/scope/index.ts#L495>
+    pub fn generate_uid(&self, name: &str) -> Atom {
         for i in 0.. {
-            let name = Self::generate_uid(name, i);
+            let name = Self::internal_generate_uid(name, i);
             if !self.has_binding(ScopeId::new(0), &name) {
                 return name;
             }
@@ -192,7 +197,8 @@ impl ScopeTree {
         unreachable!()
     }
 
-    fn generate_uid(name: &str, i: i32) -> Atom {
+    // <https://github.com/babel/babel/blob/419644f27c5c59deb19e71aaabd417a3bc5483ca/packages/babel-traverse/src/scope/index.ts#L523>
+    fn internal_generate_uid(name: &str, i: i32) -> Atom {
         Atom::from(if i > 1 { format!("_{name}{i}") } else { format!("_{name}") })
     }
 }

crates/oxc_transformer/src/es2015/mod.rs

@@ -2,6 +2,7 @@ mod arrow_functions;
 mod duplicate_keys;
 mod function_name;
 mod instanceof;
+mod new_target;
 mod shorthand_properties;
 mod template_literals;
 
@@ -9,5 +10,6 @@ pub use arrow_functions::{ArrowFunctions, ArrowFunctionsOptions};
 pub use duplicate_keys::DuplicateKeys;
 pub use function_name::FunctionName;
 pub use instanceof::Instanceof;
+pub use new_target::NewTarget;
 pub use shorthand_properties::ShorthandProperties;
 pub use template_literals::TemplateLiterals;

crates/oxc_transformer/src/es2015/new_target.rs

@@ -0,0 +1,133 @@
+use crate::{context::TransformerCtx, TransformOptions, TransformTarget};
+use oxc_allocator::Vec;
+use oxc_ast::{ast::*, AstBuilder, AstKind, VisitMut};
+use oxc_diagnostics::miette;
+use oxc_span::{Atom, Span, SPAN};
+use oxc_syntax::operator::BinaryOperator;
+use std::rc::Rc;
+
+/// ES2015: New Target
+///
+/// References:
+/// * <https://babel.dev/docs/babel-plugin-transform-template-new-target>
+/// * <https://github.com/babel/babel/blob/main/packages/babel-plugin-transform-new-target>
+pub struct NewTarget<'a> {
+    ast: Rc<AstBuilder<'a>>,
+    ctx: TransformerCtx<'a>,
+    kinds: Vec<'a, NewTargetKind>,
+}
+
+#[derive(Debug)]
+enum NewTargetKind {
+    Method,
+    Constructor,
+    Function(Option<Atom>),
+}
+
+impl<'a> VisitMut<'a> for NewTarget<'a> {
+    fn enter_node(&mut self, kind: AstKind<'a>) {
+        if let Some(kind) = self.get_kind(kind) {
+            self.kinds.push(kind);
+        }
+    }
+
+    fn leave_node(&mut self, kind: AstKind<'a>) {
+        if self.get_kind(kind).is_some() {
+            self.kinds.pop();
+        }
+    }
+}
+
+impl<'a> NewTarget<'a> {
+    pub fn new(
+        ast: Rc<AstBuilder<'a>>,
+        ctx: TransformerCtx<'a>,
+        options: &TransformOptions,
+    ) -> Option<Self> {
+        let kinds = ast.new_vec();
+        (options.target < TransformTarget::ES2015 || options.new_target).then(|| Self {
+            ast,
+            ctx,
+            kinds,
+        })
+    }
+
+    fn get_kind(&self, kind: AstKind<'a>) -> Option<NewTargetKind> {
+        match kind {
+            AstKind::MethodDefinition(def) => match def.kind {
+                MethodDefinitionKind::Get
+                | MethodDefinitionKind::Set
+                | MethodDefinitionKind::Method => Some(NewTargetKind::Method),
+                MethodDefinitionKind::Constructor => Some(NewTargetKind::Constructor),
+            },
+            AstKind::ObjectProperty(property) => property.method.then_some(NewTargetKind::Method),
+            AstKind::Function(function) => {
+                // oxc visitor `MethodDefinitionKind` will enter `Function` node, here need to exclude it
+                if let Some(kind) = self.kinds.last() {
+                    if !matches!(kind, NewTargetKind::Function(_)) {
+                        return None;
+                    }
+                }
+                function.id.as_ref().map(|id| NewTargetKind::Function(Some(id.name.clone())))
+            }
+            _ => None,
+        }
+    }
+
+    fn create_constructor_expr(&self, span: Span) -> Expression<'a> {
+        self.ast.static_member_expression(
+            span,
+            self.ast.this_expression(span),
+            IdentifierName { span, name: "constructor".into() },
+            false,
+        )
+    }
+
+    pub fn transform_expression<'b>(&mut self, expr: &'b mut Expression<'a>) {
+        if let Expression::MetaProperty(meta) = expr {
+            if meta.meta.name == "new" && meta.property.name == "target" {
+                if let Some(kind) = self.kinds.last() {
+                    match kind {
+                        NewTargetKind::Constructor => {
+                            *expr = self.create_constructor_expr(meta.span);
+                        }
+                        NewTargetKind::Method => {
+                            *expr = self.ast.void_0();
+                        }
+                        NewTargetKind::Function(name) => {
+                            // TODO packages/babel-helper-create-class-features-plugin/src/fields.ts#L192 unshadow
+                            // It will mutate previous ast node, it is difficult at now.
+                            let id = name
+                                .clone()
+                                .unwrap_or_else(|| self.ctx.scopes().generate_uid("target"));
+                            let test = self.ast.binary_expression(
+                                SPAN,
+                                self.ast.this_expression(SPAN),
+                                BinaryOperator::Instanceof,
+                                self.ast.identifier_reference_expression(IdentifierReference::new(
+                                    SPAN, id,
+                                )),
+                            );
+                            let consequent = self.ast.static_member_expression(
+                                SPAN,
+                                self.ast.this_expression(SPAN),
+                                IdentifierName { span: SPAN, name: "constructor".into() },
+                                false,
+                            );
+                            *expr = self.ast.conditional_expression(
+                                meta.span,
+                                test,
+                                consequent,
+                                self.ast.void_0(),
+                            );
+                        }
+                    }
+                } else {
+                    self.ctx.error(miette::Error::msg(
+                        "new.target must be under a (non-arrow) function or a class.",
+                    ));
+                }
+            }
+        }
+    }
+}

crates/oxc_transformer/src/lib.rs

@@ -27,7 +27,7 @@ use std::{cell::RefCell, rc::Rc, sync::Arc};
 
 use es2015::TemplateLiterals;
 use oxc_allocator::Allocator;
-use oxc_ast::{ast::*, AstBuilder, VisitMut};
+use oxc_ast::{ast::*, AstBuilder, AstKind, VisitMut};
 use oxc_diagnostics::Error;
 use oxc_semantic::Semantic;
 use oxc_span::SourceType;
@@ -69,6 +69,7 @@ pub struct Transformer<'a> {
     es2015_template_literals: Option<TemplateLiterals<'a>>,
     es2015_duplicate_keys: Option<DuplicateKeys<'a>>,
     es2015_instanceof: Option<Instanceof<'a>>,
+    es2015_new_target: Option<NewTarget<'a>>,
     es3_property_literal: Option<PropertyLiteral<'a>>,
 }
 
@@ -108,6 +109,7 @@ impl<'a> Transformer<'a> {
             es2015_template_literals: TemplateLiterals::new(Rc::clone(&ast), &options),
             es2015_duplicate_keys: DuplicateKeys::new(Rc::clone(&ast), &options),
             es2015_instanceof: Instanceof::new(Rc::clone(&ast), ctx.clone(), &options),
+            es2015_new_target: NewTarget::new(Rc::clone(&ast),ctx.clone(), &options),
             // other
             es3_property_literal: PropertyLiteral::new(Rc::clone(&ast), &options),
             react_jsx: ReactJsx::new(Rc::clone(&ast), ctx.clone(), options)
@@ -134,6 +136,14 @@ impl<'a> Transformer<'a> {
 }
 
 impl<'a> VisitMut<'a> for Transformer<'a> {
+    fn enter_node(&mut self, kind: oxc_ast::AstKind<'a>) {
+        self.es2015_new_target.as_mut().map(|t| t.enter_node(kind));
+    }
+
+    fn leave_node(&mut self, kind: oxc_ast::AstKind<'a>) {
+        self.es2015_new_target.as_mut().map(|t| t.leave_node(kind));
+    }
+
     fn visit_program(&mut self, program: &mut Program<'a>) {
         for directive in program.directives.iter_mut() {
             self.visit_directive(directive);
@@ -184,6 +194,7 @@ impl<'a> VisitMut<'a> for Transformer<'a> {
         self.es2015_instanceof.as_mut().map(|t| t.transform_expression(expr));
         self.es2016_exponentiation_operator.as_mut().map(|t| t.transform_expression(expr));
         self.es2015_template_literals.as_mut().map(|t| t.transform_expression(expr));
+        self.es2015_new_target.as_mut().map(|t| t.transform_expression(expr));
 
         self.visit_expression_match(expr);
     }
@@ -210,12 +221,14 @@ impl<'a> VisitMut<'a> for Transformer<'a> {
         self.es2015_shorthand_properties.as_mut().map(|t| t.transform_object_property(prop));
         self.es3_property_literal.as_mut().map(|t| t.transform_object_property(prop));
 
+        let kind = AstKind::ObjectProperty(self.alloc(prop));
+        self.enter_node(kind);
         self.visit_property_key(&mut prop.key);
         self.visit_expression(&mut prop.value);
-
         if let Some(init) = &mut prop.init {
             self.visit_expression(init);
         }
+        self.leave_node(kind);
     }
 
     fn visit_class_body(&mut self, class_body: &mut ClassBody<'a>) {

crates/oxc_transformer/src/options.rs

@@ -32,6 +32,7 @@ pub struct TransformOptions {
     pub property_literals: bool,
     pub babel_8_breaking: Option<bool>,
     pub instanceof: bool,
+    pub new_target: bool,
 }
 
 /// See <https://www.typescriptlang.org/tsconfig#target>

tasks/transform_conformance/babel.snap.md

@@ -1,4 +1,4 @@
-Passed: 295/1171
+Passed: 297/1179
 
 # All Passed:
 * babel-plugin-transform-numeric-separator
@@ -824,6 +824,14 @@ Passed: 295/1171
 # babel-plugin-transform-duplicate-keys (7/8)
 * combination/dupes/input.js
 
+# babel-plugin-transform-new-target (2/8)
+* general/arrow/input.js
+* general/class-properties/input.js
+* general/class-properties-loose/input.js
+* general/function/input.js
+* general/function-duplicate-name/input.js
+* general/object/input.js
+
 # babel-plugin-transform-typescript (66/158)
 * class/abstract-class-decorated/input.ts
 * class/abstract-class-decorated-method/input.ts

tasks/transform_conformance/babel_exec.snap.md

@@ -1,4 +1,4 @@
-Passed: 379/445
+Passed: 386/454
 
 # All Passed:
 * babel-plugin-transform-class-static-block
@@ -98,3 +98,7 @@ Passed: 379/445
 # babel-plugin-transform-instanceof (0/1)
 * instanceof/instanceof/exec.js
 
+# babel-plugin-transform-new-target (7/9)
+* general/class-properties/exec.js
+* general/class-properties-loose/exec.js
+

tasks/transform_conformance/src/lib.rs

@@ -82,6 +82,7 @@ const CASES: &[&str] = &[
     "babel-plugin-transform-template-literals",
     "babel-plugin-transform-duplicate-keys",
     "babel-plugin-transform-instanceof",
+    "babel-plugin-transform-new-target",
     // ES3
     "babel-plugin-transform-property-literals",
     // TypeScript

tasks/transform_conformance/src/test_case.rs

@@ -116,6 +116,7 @@ pub trait TestCase {
             template_literals: options.get_plugin("transform-template-literals").is_some(),
             property_literals: options.get_plugin("transform-property-literals").is_some(),
             duplicate_keys: options.get_plugin("transform-duplicate-keys").is_some(),
+            new_target: options.get_plugin("transform-new-target").is_some(),
         }
     }