Implement `new.target` expression (#2299)

This Pull Request changes the following:

- Implement `new.target` expression

boa_engine/src/bytecompiler/mod.rs

@@ -1301,6 +1301,11 @@ impl<'b> ByteCompiler<'b> {
                     self.emit_opcode(Opcode::Pop);
                 }
             }
+            Node::NewTarget => {
+                if use_expr {
+                    self.emit_opcode(Opcode::PushNewTarget);
+                }
+            }
             _ => unreachable!(),
         }
         Ok(())

boa_engine/src/syntax/ast/node/mod.rs

@@ -250,6 +250,9 @@ pub enum Node {
     /// A call of the super constructor. [More information](./super_call/struct.SuperCall.html).
     SuperCall(SuperCall),
 
+    /// The `new.target` pseudo-property expression.
+    NewTarget,
+
     /// A FormalParameterList.
     ///
     /// This is only used in the parser itself.
@@ -364,6 +367,7 @@ impl Node {
             Self::ClassDecl(ref decl) => decl.to_indented_string(interner, indentation),
             Self::ClassExpr(ref expr) => expr.to_indented_string(interner, indentation),
             Self::SuperCall(ref super_call) => super_call.to_interned_string(interner),
+            Self::NewTarget => "new.target".to_owned(),
             Self::FormalParameterList(_) => unreachable!(),
         }
     }
@@ -1248,6 +1252,7 @@ impl Node {
                 }
             }
             Node::Yield(_) if symbol == ContainsSymbol::YieldExpression => return true,
+            Node::NewTarget if symbol == ContainsSymbol::NewTarget => return true,
             _ => {}
         }
         false
@@ -1261,6 +1266,7 @@ pub(crate) enum ContainsSymbol {
     SuperCall,
     YieldExpression,
     AwaitExpression,
+    NewTarget,
 }
 
 impl ToInternedString for Node {

boa_engine/src/syntax/parser/expression/left_hand_side/member.rs

@@ -73,7 +73,21 @@ where
                 ));
             }
             TokenKind::Keyword((Keyword::New, false)) => {
-                let _next = cursor.next(interner).expect("new keyword disappeared");
+                cursor.next(interner).expect("token disappeared");
+
+                if cursor.next_if(Punctuator::Dot, interner)?.is_some() {
+                    let token = cursor.next(interner)?.ok_or(ParseError::AbruptEnd)?;
+                    match token.kind() {
+                        TokenKind::Identifier(Sym::TARGET) => return Ok(Node::NewTarget),
+                        _ => {
+                            return Err(ParseError::general(
+                                "unexpected private identifier",
+                                token.span().start(),
+                            ));
+                        }
+                    }
+                }
+
                 let lhs = self.parse(cursor, interner)?;
                 let args = match cursor.peek(0, interner)? {
                     Some(next) if next.kind() == &TokenKind::Punctuator(Punctuator::OpenParen) => {

boa_engine/src/syntax/parser/mod.rs

@@ -146,7 +146,7 @@ impl<R> Parser<R> {
     where
         R: Read,
     {
-        let (in_method, in_derived_constructor) = if let Some(function_env) = context
+        let (in_function, in_method, in_derived_constructor) = if let Some(function_env) = context
             .realm
             .environments
             .get_this_environment()
@@ -156,6 +156,7 @@ impl<R> Parser<R> {
             let has_super_binding = function_env_borrow.has_super_binding();
             let function_object = function_env_borrow.function_object().borrow();
             (
+                true,
                 has_super_binding,
                 function_object
                     .as_function()
@@ -163,13 +164,14 @@ impl<R> Parser<R> {
                     .is_derived_constructor(),
             )
         } else {
-            (false, false)
+            (false, false, false)
         };
 
         let statement_list = Script::new(direct).parse(&mut self.cursor, context)?;
 
         let mut contains_super_property = false;
         let mut contains_super_call = false;
+        let mut contains_new_target = false;
         if direct {
             for node in statement_list.items() {
                 if !contains_super_property && node.contains(ContainsSymbol::SuperProperty) {
@@ -179,9 +181,19 @@ impl<R> Parser<R> {
                 if !contains_super_call && node.contains(ContainsSymbol::SuperCall) {
                     contains_super_call = true;
                 }
+
+                if !contains_new_target && node.contains(ContainsSymbol::NewTarget) {
+                    contains_new_target = true;
+                }
             }
         }
 
+        if !in_function && contains_new_target {
+            return Err(ParseError::general(
+                "invalid new.target usage",
+                Position::new(1, 1),
+            ));
+        }
         if !in_method && contains_super_property {
             return Err(ParseError::general(
                 "invalid super usage",
@@ -365,10 +377,11 @@ where
         let body = self::statement::StatementList::new(false, false, false, &[])
             .parse(cursor, interner)?;
 
-        // It is a Syntax Error if StatementList Contains super unless the source text containing super is eval code that is being processed by a direct eval.
-        // Additional early error rules for super within direct eval are defined in 19.2.1.1.
         if !self.direct_eval {
             for node in body.items() {
+                // It is a Syntax Error if StatementList Contains super unless the source text containing super is eval
+                // code that is being processed by a direct eval.
+                // Additional early error rules for super within direct eval are defined in 19.2.1.1.
                 if node.contains(ContainsSymbol::SuperCall)
                     || node.contains(ContainsSymbol::SuperProperty)
                 {
@@ -377,6 +390,16 @@ where
                         Position::new(1, 1),
                     ));
                 }
+
+                // It is a Syntax Error if StatementList Contains NewTarget unless the source text containing NewTarget
+                // is eval code that is being processed by a direct eval.
+                // Additional early error rules for NewTarget in direct eval are defined in 19.2.1.1.
+                if node.contains(ContainsSymbol::NewTarget) {
+                    return Err(ParseError::general(
+                        "invalid new.target usage",
+                        Position::new(1, 1),
+                    ));
+                }
             }
         }
 

boa_engine/src/vm/code_block.rs

@@ -371,6 +371,7 @@ impl CodeBlock {
             | Opcode::PushClassField
             | Opcode::SuperCallDerived
             | Opcode::Await
+            | Opcode::PushNewTarget
             | Opcode::CallEvalSpread
             | Opcode::CallSpread
             | Opcode::NewSpread

boa_engine/src/vm/mod.rs

@@ -2501,6 +2501,22 @@ impl Context {
                 self.vm.push(JsValue::undefined());
                 return Ok(ShouldExit::Await);
             }
+            Opcode::PushNewTarget => {
+                if let Some(env) = self
+                    .realm
+                    .environments
+                    .get_this_environment()
+                    .as_function_slots()
+                {
+                    if let Some(new_target) = env.borrow().new_target() {
+                        self.vm.push(new_target.clone());
+                    } else {
+                        self.vm.push(JsValue::undefined());
+                    }
+                } else {
+                    self.vm.push(JsValue::undefined());
+                }
+            }
         }
 
         Ok(ShouldExit::False)

boa_engine/src/vm/opcode.rs

@@ -1183,6 +1183,13 @@ pub enum Opcode {
     /// Stack: promise **=>**
     Await,
 
+    /// Push the current new target to the stack.
+    ///
+    /// Operands:
+    ///
+    /// Stack: **=>** new_target
+    PushNewTarget,
+
     /// No-operation instruction, does nothing.
     ///
     /// Operands:
@@ -1364,6 +1371,7 @@ impl Opcode {
             Self::GeneratorNext => "GeneratorNext",
             Self::AsyncGeneratorNext => "AsyncGeneratorNext",
             Self::Await => "Await",
+            Self::PushNewTarget => "PushNewTarget",
             Self::GeneratorNextDelegate => "GeneratorNextDelegate",
             Self::Nop => "Nop",
         }
@@ -1509,6 +1517,7 @@ impl Opcode {
             Self::Yield => "INST - Yield",
             Self::GeneratorNext => "INST - GeneratorNext",
             Self::AsyncGeneratorNext => "INST - AsyncGeneratorNext",
+            Self::PushNewTarget => "INST - PushNewTarget",
             Self::Await => "INST - Await",
             Self::GeneratorNextDelegate => "INST - GeneratorNextDelegate",
             Self::Nop => "INST - Nop",

boa_interner/src/sym.rs

@@ -97,6 +97,9 @@ impl Sym {
     /// Symbol for the `"of"` string.
     pub const OF: Self = unsafe { Self::new_unchecked(27) };
 
+    /// Symbol for the `"target"` string.
+    pub const TARGET: Self = unsafe { Self::new_unchecked(28) };
+
     /// Creates a new [`Sym`] from the provided `value`, or returns `None` if `index` is zero.
     #[inline]
     pub(super) fn new(value: usize) -> Option<Self> {
@@ -161,6 +164,7 @@ pub(super) static COMMON_STRINGS: phf::OrderedSet<&'static str> = {
         "false",
         "async",
         "of",
+        "target",
     };
     // A `COMMON_STRINGS` of size `usize::MAX` would cause an overflow on our `Interner`
     sa::const_assert!(COMMON_STRINGS.len() < usize::MAX);