Implement `with` and object environments (#2692)

This Pull Request changes the following:

- Implement `with` statement parsing, ast node, compilation and excution.
- Implement object environments that are used in the `with` statement excution.

The implementation of object environments can probably be optimized further by using more compile-time information about when object environments can exist. Maybe there could also be a separate environment stack for object environments to reduce the filtering and iteration that is needed with the current implementation.
This does not fix all tests in the `test/language/statements/with` suite yet. But for most failing tests that I have looked at we are missing other features / have bugs elsewhere.

As a note for the review:
The functions in the `impl Context` block in `boa_engine/src/environments/runtime.rs` are mostly copied / moved from the existing functions. The only change there should be the addition of the object environment logic. They had to be moved to `Context` because of borrow semantics.

boa_ast/src/operations.rs

@@ -945,6 +945,7 @@ where
                 Statement::Try(node) => self.visit_try(node),
                 Statement::Continue(node) => self.visit_continue(node),
                 Statement::Break(node) => self.visit_break(node),
+                Statement::With(with) => self.visit_with(with),
             }
         }
 

boa_ast/src/statement/mod.rs

@@ -14,6 +14,7 @@ mod r#return;
 mod switch;
 mod throw;
 mod r#try;
+mod with;
 
 pub mod iteration;
 
@@ -26,6 +27,7 @@ pub use self::{
     r#try::{Catch, ErrorHandler, Finally, Try},
     switch::{Case, Switch},
     throw::Throw,
+    with::With,
 };
 use core::ops::ControlFlow;
 
@@ -92,7 +94,6 @@ pub enum Statement {
     /// See [`Return`].
     Return(Return),
 
-    // TODO: Possibly add `with` statements.
     /// See [`Labelled`].
     Labelled(Labelled),
 
@@ -101,6 +102,9 @@ pub enum Statement {
 
     /// See [`Try`].
     Try(Try),
+
+    /// See [`With`].
+    With(With),
 }
 
 impl Statement {
@@ -129,6 +133,7 @@ impl Statement {
             Self::Labelled(labelled) => return labelled.to_interned_string(interner),
             Self::Throw(throw) => throw.to_interned_string(interner),
             Self::Try(try_catch) => return try_catch.to_indented_string(interner, indentation),
+            Self::With(with) => return with.to_interned_string(interner),
         };
         s.push(';');
         s
@@ -208,6 +213,7 @@ impl VisitWith for Statement {
             Self::Labelled(l) => visitor.visit_labelled(l),
             Self::Throw(th) => visitor.visit_throw(th),
             Self::Try(tr) => visitor.visit_try(tr),
+            Self::With(with) => visitor.visit_with(with),
         }
     }
 
@@ -236,6 +242,7 @@ impl VisitWith for Statement {
             Self::Labelled(l) => visitor.visit_labelled_mut(l),
             Self::Throw(th) => visitor.visit_throw_mut(th),
             Self::Try(tr) => visitor.visit_try_mut(tr),
+            Self::With(with) => visitor.visit_with_mut(with),
         }
     }
 }

boa_ast/src/statement/with.rs

@@ -0,0 +1,81 @@
+use crate::{
+    expression::Expression,
+    statement::Statement,
+    try_break,
+    visitor::{VisitWith, Visitor, VisitorMut},
+};
+use boa_interner::{Interner, ToInternedString};
+use core::ops::ControlFlow;
+
+/// The `with` statement extends the scope chain for a statement.
+///
+/// More information:
+///  - [ECMAScript reference][spec]
+///  - [MDN documentation][mdn]
+///
+/// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with
+/// [spec]: https://tc39.es/ecma262/#prod-WithStatement
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
+#[derive(Clone, Debug, PartialEq)]
+pub struct With {
+    expression: Expression,
+    statement: Box<Statement>,
+}
+
+impl With {
+    /// Creates a `With` AST node.
+    #[must_use]
+    pub fn new(expression: Expression, statement: Statement) -> Self {
+        Self {
+            expression,
+            statement: Box::new(statement),
+        }
+    }
+
+    /// Gets the expression value of this `With` statement.
+    #[must_use]
+    pub const fn expression(&self) -> &Expression {
+        &self.expression
+    }
+
+    /// Gets the statement value of this `With` statement.
+    #[must_use]
+    pub const fn statement(&self) -> &Statement {
+        &self.statement
+    }
+}
+
+impl From<With> for Statement {
+    fn from(with: With) -> Self {
+        Self::With(with)
+    }
+}
+
+impl ToInternedString for With {
+    fn to_interned_string(&self, interner: &Interner) -> String {
+        format!(
+            "with ({}) {{{}}}",
+            self.expression.to_interned_string(interner),
+            self.statement.to_interned_string(interner)
+        )
+    }
+}
+
+impl VisitWith for With {
+    fn visit_with<'a, V>(&'a self, visitor: &mut V) -> ControlFlow<V::BreakTy>
+    where
+        V: Visitor<'a>,
+    {
+        try_break!(visitor.visit_expression(&self.expression));
+        visitor.visit_statement(&self.statement)
+    }
+
+    fn visit_with_mut<'a, V>(&'a mut self, visitor: &mut V) -> ControlFlow<V::BreakTy>
+    where
+        V: VisitorMut<'a>,
+    {
+        try_break!(visitor.visit_expression_mut(&mut self.expression));
+        visitor.visit_statement_mut(&mut self.statement)
+    }
+}

boa_ast/src/visitor.rs

@@ -36,7 +36,7 @@ use crate::{
             IterableLoopInitializer, WhileLoop,
         },
         Block, Case, Catch, Finally, If, Labelled, LabelledItem, Return, Statement, Switch, Throw,
-        Try,
+        Try, With,
     },
     ModuleItem, ModuleItemList, StatementList, StatementListItem,
 };
@@ -241,6 +241,7 @@ pub trait Visitor<'ast>: Sized {
     define_visit!(visit_labelled, Labelled);
     define_visit!(visit_throw, Throw);
     define_visit!(visit_try, Try);
+    define_visit!(visit_with, With);
     define_visit!(visit_identifier, Identifier);
     define_visit!(visit_formal_parameter_list, FormalParameterList);
     define_visit!(visit_class_element, ClassElement);
@@ -434,6 +435,7 @@ pub trait VisitorMut<'ast>: Sized {
     define_visit_mut!(visit_labelled_mut, Labelled);
     define_visit_mut!(visit_throw_mut, Throw);
     define_visit_mut!(visit_try_mut, Try);
+    define_visit_mut!(visit_with_mut, With);
     define_visit_mut!(visit_identifier_mut, Identifier);
     define_visit_mut!(visit_formal_parameter_list_mut, FormalParameterList);
     define_visit_mut!(visit_class_element_mut, ClassElement);

boa_engine/src/builtins/eval/mod.rs

@@ -10,13 +10,12 @@
 //! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval
 
 use crate::{
-    builtins::BuiltInObject, context::intrinsics::Intrinsics, environments::DeclarativeEnvironment,
+    builtins::BuiltInObject, context::intrinsics::Intrinsics, environments::Environment,
     error::JsNativeError, object::JsObject, Context, JsArgs, JsResult, JsString, JsValue,
 };
 use boa_ast::operations::{
     contains, contains_arguments, top_level_var_declared_names, ContainsSymbol,
 };
-use boa_gc::Gc;
 use boa_parser::{Parser, Source};
 use boa_profiler::Profiler;
 
@@ -85,7 +84,7 @@ impl Eval {
         #[derive(Debug)]
         enum EnvStackAction {
             Truncate(usize),
-            Restore(Vec<Gc<DeclarativeEnvironment>>),
+            Restore(Vec<Environment>),
         }
 
         /// Restores the environment after calling `eval` or after throwing an error.

boa_engine/src/bytecompiler/statement/mod.rs

@@ -10,6 +10,7 @@ mod labelled;
 mod r#loop;
 mod switch;
 mod r#try;
+mod with;
 
 impl ByteCompiler<'_, '_> {
     /// Compiles a [`Statement`] `boa_ast` node.
@@ -56,8 +57,9 @@ impl ByteCompiler<'_, '_> {
                 self.emit(Opcode::Return, &[]);
             }
             Statement::Try(t) => self.compile_try(t, use_expr, configurable_globals),
-            Statement::Empty => {}
             Statement::Expression(expr) => self.compile_expr(expr, use_expr),
+            Statement::With(with) => self.compile_with(with, configurable_globals),
+            Statement::Empty => {}
         }
     }
 }

boa_engine/src/bytecompiler/statement/with.rs

@@ -0,0 +1,14 @@
+use crate::{bytecompiler::ByteCompiler, vm::Opcode};
+use boa_ast::statement::With;
+
+impl ByteCompiler<'_, '_> {
+    /// Compile a [`With`] `boa_ast` node
+    pub(crate) fn compile_with(&mut self, with: &With, configurable_globals: bool) {
+        self.compile_expr(with.expression(), true);
+        self.context.push_compile_time_environment(false);
+        self.emit_opcode(Opcode::PushObjectEnvironment);
+        self.compile_stmt(with.statement(), false, configurable_globals);
+        self.context.pop_compile_time_environment();
+        self.emit_opcode(Opcode::PopEnvironment);
+    }
+}

boa_engine/src/environments/mod.rs

@@ -30,7 +30,8 @@ mod runtime;
 pub(crate) use {
     compile::CompileTimeEnvironment,
     runtime::{
-        BindingLocator, DeclarativeEnvironment, DeclarativeEnvironmentStack, EnvironmentSlots,
+        BindingLocator, DeclarativeEnvironment, DeclarativeEnvironmentStack, Environment,
+        EnvironmentSlots,
     },
 };
 

boa_engine/src/environments/runtime.rs

@@ -1,5 +1,6 @@
 use crate::{
-    environments::CompileTimeEnvironment, error::JsNativeError, object::JsObject, Context, JsValue,
+    environments::CompileTimeEnvironment, error::JsNativeError, object::JsObject, Context,
+    JsResult, JsString, JsSymbol, JsValue,
 };
 use boa_ast::expression::Identifier;
 use boa_gc::{Finalize, Gc, GcRefCell, Trace};
@@ -32,6 +33,8 @@ pub(crate) struct DeclarativeEnvironment {
     compile: Gc<GcRefCell<CompileTimeEnvironment>>,
     #[unsafe_ignore_trace]
     poisoned: Cell<bool>,
+    #[unsafe_ignore_trace]
+    with: Cell<bool>,
     slots: Option<EnvironmentSlots>,
 }
 
@@ -214,25 +217,49 @@ impl DeclarativeEnvironment {
     }
 }
 
-/// A declarative environment stack holds all declarative environments at runtime.
+/// The environment stack holds all environments at runtime.
 ///
 /// Environments themselves are garbage collected,
 /// because they must be preserved for function calls.
 #[derive(Clone, Debug, Trace, Finalize)]
 pub struct DeclarativeEnvironmentStack {
-    stack: Vec<Gc<DeclarativeEnvironment>>,
+    stack: Vec<Environment>,
+}
+
+/// A runtime environment.
+#[derive(Clone, Debug, Trace, Finalize)]
+pub(crate) enum Environment {
+    Declarative(Gc<DeclarativeEnvironment>),
+    Object(JsObject),
+}
+
+impl Environment {
+    /// Returns the declarative environment if it is one.
+    pub(crate) const fn as_declarative(&self) -> Option<&Gc<DeclarativeEnvironment>> {
+        match self {
+            Self::Declarative(env) => Some(env),
+            Self::Object(_) => None,
+        }
+    }
+
+    /// Returns the declarative environment and panic if it is not one.
+    pub(crate) fn declarative_expect(&self) -> &Gc<DeclarativeEnvironment> {
+        self.as_declarative()
+            .expect("environment must be declarative")
+    }
 }
 
 impl DeclarativeEnvironmentStack {
     /// Create a new environment stack with the most outer declarative environment.
     pub(crate) fn new(global_compile_environment: Gc<GcRefCell<CompileTimeEnvironment>>) -> Self {
         Self {
-            stack: vec![Gc::new(DeclarativeEnvironment {
+            stack: Vec::from([Environment::Declarative(Gc::new(DeclarativeEnvironment {
                 bindings: GcRefCell::new(Vec::new()),
                 compile: global_compile_environment,
                 poisoned: Cell::new(false),
+                with: Cell::new(false),
                 slots: Some(EnvironmentSlots::Global),
-            })],
+            }))]),
         }
     }
 
@@ -240,7 +267,12 @@ impl DeclarativeEnvironmentStack {
     ///
     /// This is only useful when compiled bindings are added after the initial compilation (eval).
     pub(crate) fn extend_outer_function_environment(&mut self) {
-        for env in self.stack.iter().rev() {
+        for env in self
+            .stack
+            .iter()
+            .filter_map(Environment::as_declarative)
+            .rev()
+        {
             if let Some(EnvironmentSlots::Function(_)) = env.slots {
                 let compile_bindings_number = env.compile.borrow().num_bindings();
                 let mut bindings_mut = env.bindings.borrow_mut();
@@ -262,7 +294,12 @@ impl DeclarativeEnvironmentStack {
         &self,
         names: &FxHashSet<Identifier>,
     ) -> Option<Identifier> {
-        for env in self.stack.iter().rev() {
+        for env in self
+            .stack
+            .iter()
+            .filter_map(Environment::as_declarative)
+            .rev()
+        {
             let compile = env.compile.borrow();
             for name in names {
                 if compile.has_lex_binding(*name) {
@@ -277,7 +314,7 @@ impl DeclarativeEnvironmentStack {
     }
 
     /// Pop all current environments except the global environment.
-    pub(crate) fn pop_to_global(&mut self) -> Vec<Gc<DeclarativeEnvironment>> {
+    pub(crate) fn pop_to_global(&mut self) -> Vec<Environment> {
         self.stack.split_off(1)
     }
 
@@ -292,7 +329,7 @@ impl DeclarativeEnvironmentStack {
     }
 
     /// Extend the current environment stack with the given environments.
-    pub(crate) fn extend(&mut self, other: Vec<Gc<DeclarativeEnvironment>>) {
+    pub(crate) fn extend(&mut self, other: Vec<Environment>) {
         self.stack.extend(other);
     }
 
@@ -305,7 +342,8 @@ impl DeclarativeEnvironmentStack {
         let environment = self
             .stack
             .get(0)
-            .expect("global environment must always exist");
+            .and_then(Environment::as_declarative)
+            .expect("global environment must be declarative and exist");
         let mut bindings = environment.bindings.borrow_mut();
         if bindings.len() < binding_number {
             bindings.resize(binding_number, None);
@@ -325,7 +363,12 @@ impl DeclarativeEnvironmentStack {
     ///
     /// Panics if no environment exists on the stack.
     pub(crate) fn get_this_environment(&self) -> &EnvironmentSlots {
-        for env in self.stack.iter().rev() {
+        for env in self
+            .stack
+            .iter()
+            .filter_map(Environment::as_declarative)
+            .rev()
+        {
             if let Some(slots) = &env.slots {
                 match slots {
                     EnvironmentSlots::Function(function_env) => {
@@ -341,6 +384,13 @@ impl DeclarativeEnvironmentStack {
         panic!("global environment must exist")
     }
 
+    /// Push a new object environment on the environments stack and return it's index.
+    pub(crate) fn push_object(&mut self, object: JsObject) -> usize {
+        let index = self.stack.len();
+        self.stack.push(Environment::Object(object));
+        index
+    }
+
     /// Push a declarative environment on the environments stack and return it's index.
     ///
     /// # Panics
@@ -351,21 +401,33 @@ impl DeclarativeEnvironmentStack {
         num_bindings: usize,
         compile_environment: Gc<GcRefCell<CompileTimeEnvironment>>,
     ) -> usize {
-        let poisoned = self
-            .stack
-            .last()
-            .expect("global environment must always exist")
-            .poisoned
-            .get();
+        let (poisoned, with) = {
+            let with = self
+                .stack
+                .last()
+                .expect("global environment must always exist")
+                .as_declarative()
+                .is_none();
+
+            let environment = self
+                .stack
+                .iter()
+                .filter_map(Environment::as_declarative)
+                .last()
+                .expect("global environment must always exist");
+            (environment.poisoned.get(), with || environment.with.get())
+        };
 
         let index = self.stack.len();
 
-        self.stack.push(Gc::new(DeclarativeEnvironment {
-            bindings: GcRefCell::new(vec![None; num_bindings]),
-            compile: compile_environment,
-            poisoned: Cell::new(poisoned),
-            slots: None,
-        }));
+        self.stack
+            .push(Environment::Declarative(Gc::new(DeclarativeEnvironment {
+                bindings: GcRefCell::new(vec![None; num_bindings]),
+                compile: compile_environment,
+                poisoned: Cell::new(poisoned),
+                with: Cell::new(with),
+                slots: None,
+            })));
 
         index
     }
@@ -384,12 +446,22 @@ impl DeclarativeEnvironmentStack {
         new_target: Option<JsObject>,
         lexical: bool,
     ) {
-        let outer = self
-            .stack
-            .last()
-            .expect("global environment must always exist");
-
-        let poisoned = outer.poisoned.get();
+        let (poisoned, with) = {
+            let with = self
+                .stack
+                .last()
+                .expect("global environment must always exist")
+                .as_declarative()
+                .is_none();
+
+            let environment = self
+                .stack
+                .iter()
+                .filter_map(Environment::as_declarative)
+                .last()
+                .expect("global environment must always exist");
+            (environment.poisoned.get(), with || environment.with.get())
+        };
 
         let this_binding_status = if lexical {
             ThisBindingStatus::Lexical
@@ -401,17 +473,19 @@ impl DeclarativeEnvironmentStack {
 
         let this = this.unwrap_or(JsValue::Null);
 
-        self.stack.push(Gc::new(DeclarativeEnvironment {
-            bindings: GcRefCell::new(vec![None; num_bindings]),
-            compile: compile_environment,
-            poisoned: Cell::new(poisoned),
-            slots: Some(EnvironmentSlots::Function(GcRefCell::new(FunctionSlots {
-                this,
-                this_binding_status,
-                function_object,
-                new_target,
-            }))),
-        }));
+        self.stack
+            .push(Environment::Declarative(Gc::new(DeclarativeEnvironment {
+                bindings: GcRefCell::new(vec![None; num_bindings]),
+                compile: compile_environment,
+                poisoned: Cell::new(poisoned),
+                with: Cell::new(with),
+                slots: Some(EnvironmentSlots::Function(GcRefCell::new(FunctionSlots {
+                    this,
+                    this_binding_status,
+                    function_object,
+                    new_target,
+                }))),
+            })));
     }
 
     /// Push a function environment that inherits it's internal slots from the outer environment.
@@ -424,24 +498,39 @@ impl DeclarativeEnvironmentStack {
         num_bindings: usize,
         compile_environment: Gc<GcRefCell<CompileTimeEnvironment>>,
     ) {
-        let outer = self
-            .stack
-            .last()
-            .expect("global environment must always exist");
-
-        let poisoned = outer.poisoned.get();
-        let slots = outer.slots.clone();
+        let (poisoned, with, slots) = {
+            let with = self
+                .stack
+                .last()
+                .expect("global environment must always exist")
+                .as_declarative()
+                .is_none();
+
+            let environment = self
+                .stack
+                .iter()
+                .filter_map(Environment::as_declarative)
+                .last()
+                .expect("global environment must always exist");
+            (
+                environment.poisoned.get(),
+                with || environment.with.get(),
+                environment.slots.clone(),
+            )
+        };
 
-        self.stack.push(Gc::new(DeclarativeEnvironment {
-            bindings: GcRefCell::new(vec![None; num_bindings]),
-            compile: compile_environment,
-            poisoned: Cell::new(poisoned),
-            slots,
-        }));
+        self.stack
+            .push(Environment::Declarative(Gc::new(DeclarativeEnvironment {
+                bindings: GcRefCell::new(vec![None; num_bindings]),
+                compile: compile_environment,
+                poisoned: Cell::new(poisoned),
+                with: Cell::new(with),
+                slots,
+            })));
     }
 
     /// Pop environment from the environments stack.
-    pub(crate) fn pop(&mut self) -> Gc<DeclarativeEnvironment> {
+    pub(crate) fn pop(&mut self) -> Environment {
         debug_assert!(self.stack.len() > 1);
         self.stack
             .pop()
@@ -454,7 +543,12 @@ impl DeclarativeEnvironmentStack {
     ///
     /// Panics if no environment exists on the stack.
     pub(crate) fn current_function_slots(&self) -> &EnvironmentSlots {
-        for env in self.stack.iter().rev() {
+        for env in self
+            .stack
+            .iter()
+            .filter_map(Environment::as_declarative)
+            .rev()
+        {
             if let Some(slots) = &env.slots {
                 return slots;
             }
@@ -472,6 +566,7 @@ impl DeclarativeEnvironmentStack {
         self.stack
             .last()
             .expect("global environment must always exist")
+            .declarative_expect()
             .clone()
     }
 
@@ -482,6 +577,8 @@ impl DeclarativeEnvironmentStack {
     /// Panics if no environment exists on the stack.
     pub(crate) fn current_compile_environment(&self) -> Gc<GcRefCell<CompileTimeEnvironment>> {
         self.stack
+            .iter()
+            .filter_map(Environment::as_declarative)
             .last()
             .expect("global environment must always exist")
             .compile
@@ -495,6 +592,8 @@ impl DeclarativeEnvironmentStack {
     /// Panics if no environment exists on the stack.
     pub(crate) fn poison_current(&mut self) {
         self.stack
+            .iter()
+            .filter_map(Environment::as_declarative)
             .last()
             .expect("global environment must always exist")
             .poisoned
@@ -504,14 +603,16 @@ impl DeclarativeEnvironmentStack {
     /// Mark that there may be added binding in all environments.
     pub(crate) fn poison_all(&mut self) {
         for env in &mut self.stack {
-            if env.poisoned.get() {
-                return;
+            if let Some(env) = env.as_declarative() {
+                if env.poisoned.get() {
+                    return;
+                }
+                env.poisoned.set(true);
             }
-            env.poisoned.set(true);
         }
     }
 
-    /// Get the value of a binding.
+    /// Get the value of a binding. Ignores object environments.
     ///
     /// # Panics
     ///
@@ -524,10 +625,12 @@ impl DeclarativeEnvironmentStack {
     ) -> Option<JsValue> {
         if environment_index != self.stack.len() - 1 {
             for env_index in (environment_index + 1..self.stack.len()).rev() {
-                let env = self
+                let Environment::Declarative(env) = self
                     .stack
                     .get(env_index)
-                    .expect("environment index must be in range");
+                    .expect("environment index must be in range") else {
+                    continue;
+                };
                 if !env.poisoned.get() {
                     break;
                 }
@@ -545,6 +648,7 @@ impl DeclarativeEnvironmentStack {
         self.stack
             .get(environment_index)
             .expect("environment index must be in range")
+            .declarative_expect()
             .bindings
             .borrow()
             .get(binding_index)
@@ -552,33 +656,6 @@ impl DeclarativeEnvironmentStack {
             .clone()
     }
 
-    /// Get the value of a binding by it's name.
-    ///
-    /// This only considers function environments that are poisoned.
-    /// All other bindings are accessed via indices.
-    pub(crate) fn get_value_if_global_poisoned(&self, name: Identifier) -> Option<JsValue> {
-        for env in self.stack.iter().rev() {
-            if !env.poisoned.get() {
-                return None;
-            }
-            let compile = env.compile.borrow();
-            if compile.is_function() {
-                if let Some(b) = compile.get_binding(name) {
-                    return self
-                        .stack
-                        .get(b.environment_index)
-                        .expect("environment index must be in range")
-                        .bindings
-                        .borrow()
-                        .get(b.binding_index)
-                        .expect("binding index must be in range")
-                        .clone();
-                }
-            }
-        }
-        None
-    }
-
     /// Set the value of a binding.
     ///
     /// # Panics
@@ -594,6 +671,7 @@ impl DeclarativeEnvironmentStack {
             .stack
             .get(environment_index)
             .expect("environment index must be in range")
+            .declarative_expect()
             .bindings
             .borrow_mut();
         let binding = bindings
@@ -602,56 +680,6 @@ impl DeclarativeEnvironmentStack {
         *binding = Some(value);
     }
 
-    /// Set the value of a binding if it is initialized.
-    /// Return `true` if the value has been set.
-    ///
-    /// # Panics
-    ///
-    /// Panics if the environment or binding index are out of range.
-    pub(crate) fn put_value_if_initialized(
-        &mut self,
-        mut environment_index: usize,
-        mut binding_index: usize,
-        name: Identifier,
-        value: JsValue,
-    ) -> bool {
-        if environment_index != self.stack.len() - 1 {
-            for env_index in (environment_index + 1..self.stack.len()).rev() {
-                let env = self
-                    .stack
-                    .get(env_index)
-                    .expect("environment index must be in range");
-                if !env.poisoned.get() {
-                    break;
-                }
-                let compile = env.compile.borrow();
-                if compile.is_function() {
-                    if let Some(b) = compile.get_binding(name) {
-                        environment_index = b.environment_index;
-                        binding_index = b.binding_index;
-                        break;
-                    }
-                }
-            }
-        }
-
-        let mut bindings = self
-            .stack
-            .get(environment_index)
-            .expect("environment index must be in range")
-            .bindings
-            .borrow_mut();
-        let binding = bindings
-            .get_mut(binding_index)
-            .expect("binding index must be in range");
-        if binding.is_none() {
-            false
-        } else {
-            *binding = Some(value);
-            true
-        }
-    }
-
     /// Set the value of a binding if it is uninitialized.
     ///
     /// # Panics
@@ -667,6 +695,7 @@ impl DeclarativeEnvironmentStack {
             .stack
             .get(environment_index)
             .expect("environment index must be in range")
+            .declarative_expect()
             .bindings
             .borrow_mut();
         let binding = bindings
@@ -677,44 +706,7 @@ impl DeclarativeEnvironmentStack {
         }
     }
 
-    /// Set the value of a binding by it's name.
-    ///
-    /// This only considers function environments that are poisoned.
-    /// All other bindings are set via indices.
-    ///
-    /// # Panics
-    ///
-    /// Panics if the environment or binding index are out of range.
-    pub(crate) fn put_value_if_global_poisoned(
-        &mut self,
-        name: Identifier,
-        value: &JsValue,
-    ) -> bool {
-        for env in self.stack.iter().rev() {
-            if !env.poisoned.get() {
-                return false;
-            }
-            let compile = env.compile.borrow();
-            if compile.is_function() {
-                if let Some(b) = compile.get_binding(name) {
-                    let mut bindings = self
-                        .stack
-                        .get(b.environment_index)
-                        .expect("environment index must be in range")
-                        .bindings
-                        .borrow_mut();
-                    let binding = bindings
-                        .get_mut(b.binding_index)
-                        .expect("binding index must be in range");
-                    *binding = Some(value.clone());
-                    return true;
-                }
-            }
-        }
-        false
-    }
-
-    /// Checks if the name only exists as a global property.
+    /// Check if a binding name does exist in a poisoned environment.
     ///
     /// A binding could be marked as `global`, and at the same time, exist in a deeper environment
     /// context; if the global context is poisoned, an `eval` call could have added a binding that is
@@ -723,25 +715,26 @@ impl DeclarativeEnvironmentStack {
     ///
     /// # Panics
     ///
-    /// Panics if the environment or binding index are out of range.
-    pub(crate) fn is_only_global_property(&mut self, name: Identifier) -> bool {
+    /// Panics if the global environment does not exist.
+    pub(crate) fn binding_in_poisoned_environment(&mut self, name: Identifier) -> bool {
         for env in self
             .stack
             .split_first()
             .expect("global environment must exist")
             .1
             .iter()
+            .filter_map(Environment::as_declarative)
             .rev()
         {
             if !env.poisoned.get() {
-                return true;
+                return false;
             }
             let compile = env.compile.borrow();
             if compile.is_function() && compile.get_binding(name).is_some() {
-                return false;
+                return true;
             }
         }
-        true
+        false
     }
 }
 
@@ -852,3 +845,287 @@ impl BindingLocator {
         }
     }
 }
+
+impl Context<'_> {
+    /// Get the value of a binding.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the environment or binding index are out of range.
+    pub(crate) fn get_value_optional(
+        &mut self,
+        mut environment_index: usize,
+        mut binding_index: usize,
+        name: Identifier,
+    ) -> JsResult<Option<JsValue>> {
+        for env_index in (environment_index + 1..self.realm.environments.stack.len()).rev() {
+            match self.environment_expect(env_index) {
+                Environment::Declarative(env) => {
+                    if env.poisoned.get() {
+                        let compile = env.compile.borrow();
+                        if compile.is_function() {
+                            if let Some(b) = compile.get_binding(name) {
+                                environment_index = b.environment_index;
+                                binding_index = b.binding_index;
+                                break;
+                            }
+                        }
+                    } else if !env.with.get() {
+                        break;
+                    }
+                }
+                Environment::Object(o) => {
+                    let o = o.clone();
+                    let key: JsString = self
+                        .interner()
+                        .resolve_expect(name.sym())
+                        .into_common(false);
+                    if o.has_property(key.clone(), self)? {
+                        if let Some(unscopables) = o.get(JsSymbol::unscopables(), self)?.as_object()
+                        {
+                            if unscopables.get(key.clone(), self)?.to_boolean() {
+                                continue;
+                            }
+                        }
+                        return o.get(key, self).map(Some);
+                    }
+                }
+            }
+        }
+
+        Ok(self
+            .environment_expect(environment_index)
+            .declarative_expect()
+            .bindings
+            .borrow()
+            .get(binding_index)
+            .expect("binding index must be in range")
+            .clone())
+    }
+
+    /// Get the value of a binding by it's name.
+    ///
+    /// This only considers function environments that are poisoned.
+    /// All other bindings are accessed via indices.
+    pub(crate) fn get_value_if_global_poisoned(
+        &mut self,
+        name: Identifier,
+    ) -> JsResult<Option<JsValue>> {
+        for env_index in (0..self.realm.environments.stack.len()).rev() {
+            let env = self.environment_expect(env_index);
+
+            match env {
+                Environment::Declarative(env) => {
+                    if env.poisoned.get() {
+                        let compile = env.compile.borrow();
+                        if compile.is_function() {
+                            if let Some(b) = compile.get_binding(name) {
+                                return Ok(self
+                                    .environment_expect(b.environment_index)
+                                    .declarative_expect()
+                                    .bindings
+                                    .borrow()
+                                    .get(b.binding_index)
+                                    .expect("binding index must be in range")
+                                    .clone());
+                            }
+                        } else if !env.with.get() {
+                            return Ok(None);
+                        }
+                    }
+                }
+                Environment::Object(o) => {
+                    let o = o.clone();
+                    let key: JsString = self
+                        .interner()
+                        .resolve_expect(name.sym())
+                        .into_common(false);
+                    if o.has_property(key.clone(), self)? {
+                        if let Some(unscopables) = o.get(JsSymbol::unscopables(), self)?.as_object()
+                        {
+                            if unscopables.get(key.clone(), self)?.to_boolean() {
+                                continue;
+                            }
+                        }
+                        return o.get(key, self).map(Some);
+                    }
+                }
+            }
+        }
+
+        Ok(None)
+    }
+
+    /// Set the value of a binding if it is initialized.
+    /// Return `true` if the value has been set.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the environment or binding index are out of range.
+    pub(crate) fn put_value_if_initialized(
+        &mut self,
+        mut environment_index: usize,
+        mut binding_index: usize,
+        name: Identifier,
+        value: JsValue,
+    ) -> JsResult<bool> {
+        for env_index in (environment_index + 1..self.realm.environments.stack.len()).rev() {
+            let env = self.environment_expect(env_index);
+
+            match env {
+                Environment::Declarative(env) => {
+                    if env.poisoned.get() {
+                        let compile = env.compile.borrow();
+                        if compile.is_function() {
+                            if let Some(b) = compile.get_binding(name) {
+                                environment_index = b.environment_index;
+                                binding_index = b.binding_index;
+                                break;
+                            }
+                        }
+                    } else if !env.with.get() {
+                        break;
+                    }
+                }
+                Environment::Object(o) => {
+                    let o = o.clone();
+                    let key: JsString = self
+                        .interner()
+                        .resolve_expect(name.sym())
+                        .into_common(false);
+                    if o.has_property(key.clone(), self)? {
+                        if let Some(unscopables) = o.get(JsSymbol::unscopables(), self)?.as_object()
+                        {
+                            if unscopables.get(key.clone(), self)?.to_boolean() {
+                                continue;
+                            }
+                        }
+                        return o.set(key, value, true, self);
+                    }
+                }
+            }
+        }
+
+        let mut bindings = self
+            .environment_expect(environment_index)
+            .declarative_expect()
+            .bindings
+            .borrow_mut();
+        let binding = bindings
+            .get_mut(binding_index)
+            .expect("binding index must be in range");
+        if binding.is_none() {
+            Ok(false)
+        } else {
+            *binding = Some(value);
+            Ok(true)
+        }
+    }
+
+    /// Set the value of a binding by it's name.
+    ///
+    /// This only considers function environments that are poisoned.
+    /// All other bindings are set via indices.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the environment or binding index are out of range.
+    pub(crate) fn put_value_if_global_poisoned(
+        &mut self,
+        name: Identifier,
+        value: &JsValue,
+    ) -> JsResult<bool> {
+        for env_index in (0..self.realm.environments.stack.len()).rev() {
+            let env = self.environment_expect(env_index);
+
+            match env {
+                Environment::Declarative(env) => {
+                    if env.poisoned.get() {
+                        let compile = env.compile.borrow();
+                        if compile.is_function() {
+                            if let Some(b) = compile.get_binding(name) {
+                                let mut bindings = self
+                                    .environment_expect(b.environment_index)
+                                    .declarative_expect()
+                                    .bindings
+                                    .borrow_mut();
+                                let binding = bindings
+                                    .get_mut(b.binding_index)
+                                    .expect("binding index must be in range");
+                                *binding = Some(value.clone());
+                                return Ok(true);
+                            }
+                        }
+                    } else if !env.with.get() {
+                        return Ok(false);
+                    }
+                }
+                Environment::Object(o) => {
+                    let o = o.clone();
+                    let key: JsString = self
+                        .interner()
+                        .resolve_expect(name.sym())
+                        .into_common(false);
+                    if o.has_property(key.clone(), self)? {
+                        if let Some(unscopables) = o.get(JsSymbol::unscopables(), self)?.as_object()
+                        {
+                            if unscopables.get(key.clone(), self)?.to_boolean() {
+                                continue;
+                            }
+                        }
+                        return o.set(key, value.clone(), true, self);
+                    }
+                }
+            }
+        }
+
+        Ok(false)
+    }
+
+    /// Delete a binding form an object environment if it exists.
+    ///
+    /// Returns a tuple of `(found, deleted)`.
+    pub(crate) fn delete_binding_from_objet_environment(
+        &mut self,
+        name: Identifier,
+    ) -> JsResult<(bool, bool)> {
+        for env_index in (0..self.realm.environments.stack.len()).rev() {
+            let env = self.environment_expect(env_index);
+
+            match env {
+                Environment::Object(o) => {
+                    let o = o.clone();
+                    let key: JsString = self
+                        .interner()
+                        .resolve_expect(name.sym())
+                        .into_common(false);
+                    if o.has_property(key.clone(), self)? {
+                        if let Some(unscopables) = o.get(JsSymbol::unscopables(), self)?.as_object()
+                        {
+                            if unscopables.get(key.clone(), self)?.to_boolean() {
+                                continue;
+                            }
+                        }
+                        return Ok((true, o.__delete__(&key.into(), self)?));
+                    }
+                }
+                Environment::Declarative(env) => {
+                    if !env.with.get() {
+                        return Ok((false, false));
+                    }
+                }
+            }
+        }
+
+        Ok((false, false))
+    }
+
+    /// Return the environment at the given index. Panics if the index is out of range.
+    fn environment_expect(&self, index: usize) -> &Environment {
+        self.realm
+            .environments
+            .stack
+            .get(index)
+            .expect("environment index must be in range")
+    }
+}

boa_engine/src/tests/mod.rs

@@ -403,7 +403,7 @@ fn strict_mode_with() {
             }
         "#},
         ErrorKind::Syntax,
-        "unexpected token 'with', primary expression at line 3, col 5",
+        "with statement not allowed in strict mode at line 3, col 5",
     )]);
 }
 

boa_engine/src/vm/code_block.rs

@@ -444,6 +444,7 @@ impl CodeBlock {
             | Opcode::SuperCallSpread
             | Opcode::ForAwaitOfLoopIterate
             | Opcode::SetPrototype
+            | Opcode::PushObjectEnvironment
             | Opcode::Nop => String::new(),
         }
     }
@@ -1474,6 +1475,7 @@ impl JsObject {
                         .into())
                 } else {
                     let function_env = environment
+                        .declarative_expect()
                         .slots()
                         .expect("must be function environment")
                         .as_function_slots()

boa_engine/src/vm/flowgraph/mod.rs

@@ -515,7 +515,8 @@ impl CodeBlock {
                 | Opcode::SuperCallSpread
                 | Opcode::ForAwaitOfLoopIterate
                 | Opcode::SetPrototype
-                | Opcode::Nop => {
+                | Opcode::Nop
+                | Opcode::PushObjectEnvironment => {
                     graph.add_node(previous_pc, NodeShape::None, label.into(), Color::None);
                     graph.add_edge(previous_pc, pc, None, Color::None, EdgeStyle::Line);
                 }

boa_engine/src/vm/opcode/define/mod.rs

@@ -70,12 +70,16 @@ impl Operation for DefInitVar {
         binding_locator.throw_mutate_immutable(context)?;
 
         if binding_locator.is_global() {
-            let key = context
-                .interner()
-                .resolve_expect(binding_locator.name().sym())
-                .into_common::<JsString>(false)
-                .into();
-            crate::object::internal_methods::global::global_set_no_receiver(&key, value, context)?;
+            if !context.put_value_if_global_poisoned(binding_locator.name(), &value)? {
+                let key = context
+                    .interner()
+                    .resolve_expect(binding_locator.name().sym())
+                    .into_common::<JsString>(false)
+                    .into();
+                crate::object::internal_methods::global::global_set_no_receiver(
+                    &key, value, context,
+                )?;
+            }
         } else {
             context.realm.environments.put_value(
                 binding_locator.environment_index(),

boa_engine/src/vm/opcode/delete/mod.rs

@@ -80,11 +80,18 @@ impl Operation for DeleteName {
         binding_locator.throw_mutate_immutable(context)?;
 
         let deleted = if binding_locator.is_global()
-            && context
+            && !context
                 .realm
                 .environments
-                .is_only_global_property(binding_locator.name())
+                .binding_in_poisoned_environment(binding_locator.name())
         {
+            let (found, deleted) =
+                context.delete_binding_from_objet_environment(binding_locator.name())?;
+            if found {
+                context.vm.push(deleted);
+                return Ok(CompletionType::Normal);
+            }
+
             let key: JsString = context
                 .interner()
                 .resolve_expect(binding_locator.name().sym())

boa_engine/src/vm/opcode/get/name.rs

@@ -22,11 +22,7 @@ impl Operation for GetName {
         binding_locator.throw_mutate_immutable(context)?;
 
         let value = if binding_locator.is_global() {
-            if let Some(value) = context
-                .realm
-                .environments
-                .get_value_if_global_poisoned(binding_locator.name())
-            {
+            if let Some(value) = context.get_value_if_global_poisoned(binding_locator.name())? {
                 value
             } else {
                 let key: JsString = context
@@ -58,11 +54,11 @@ impl Operation for GetName {
                     }
                 }
             }
-        } else if let Some(value) = context.realm.environments.get_value_optional(
+        } else if let Some(value) = context.get_value_optional(
             binding_locator.environment_index(),
             binding_locator.binding_index(),
             binding_locator.name(),
-        ) {
+        )? {
             value
         } else {
             let name = context
@@ -95,11 +91,7 @@ impl Operation for GetNameOrUndefined {
         let binding_locator = context.vm.frame().code_block.bindings[index as usize];
         binding_locator.throw_mutate_immutable(context)?;
         let value = if binding_locator.is_global() {
-            if let Some(value) = context
-                .realm
-                .environments
-                .get_value_if_global_poisoned(binding_locator.name())
-            {
+            if let Some(value) = context.get_value_if_global_poisoned(binding_locator.name())? {
                 value
             } else {
                 let key: JsString = context
@@ -120,11 +112,11 @@ impl Operation for GetNameOrUndefined {
                     _ => JsValue::undefined(),
                 }
             }
-        } else if let Some(value) = context.realm.environments.get_value_optional(
+        } else if let Some(value) = context.get_value_optional(
             binding_locator.environment_index(),
             binding_locator.binding_index(),
             binding_locator.name(),
-        ) {
+        )? {
             value
         } else {
             JsValue::undefined()

boa_engine/src/vm/opcode/mod.rs

@@ -1308,6 +1308,13 @@ generate_impl! {
         /// Stack: **=>**
         PushDeclarativeEnvironment,
 
+        /// Push an object environment.
+        ///
+        /// Operands:
+        ///
+        /// Stack: object **=>**
+        PushObjectEnvironment,
+
         /// Push a function environment.
         ///
         /// Operands: num_bindings: `u32`, compile_environments_index: `u32`

boa_engine/src/vm/opcode/push/environment.rs

@@ -53,3 +53,24 @@ impl Operation for PushFunctionEnvironment {
         Ok(CompletionType::Normal)
     }
 }
+
+/// `PushObjectEnvironment` implements the Opcode Operation for `Opcode::PushObjectEnvironment`
+///
+/// Operation:
+///  - Push an object environment
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct PushObjectEnvironment;
+
+impl Operation for PushObjectEnvironment {
+    const NAME: &'static str = "PushObjectEnvironment";
+    const INSTRUCTION: &'static str = "INST - PushObjectEnvironment";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let object = context.vm.pop();
+        let object = object.to_object(context)?;
+
+        context.realm.environments.push_object(object);
+        context.vm.frame_mut().inc_frame_env_stack();
+        Ok(CompletionType::Normal)
+    }
+}

boa_engine/src/vm/opcode/set/name.rs

@@ -25,11 +25,7 @@ impl Operation for SetName {
         binding_locator.throw_mutate_immutable(context)?;
 
         if binding_locator.is_global() {
-            if !context
-                .realm
-                .environments
-                .put_value_if_global_poisoned(binding_locator.name(), &value)
-            {
+            if !context.put_value_if_global_poisoned(binding_locator.name(), &value)? {
                 let key: JsString = context
                     .interner()
                     .resolve_expect(binding_locator.name().sym())
@@ -60,12 +56,12 @@ impl Operation for SetName {
                         .into());
                 }
             }
-        } else if !context.realm.environments.put_value_if_initialized(
+        } else if !context.put_value_if_initialized(
             binding_locator.environment_index(),
             binding_locator.binding_index(),
             binding_locator.name(),
             value,
-        ) {
+        )? {
             return Err(JsNativeError::reference()
                 .with_message(format!(
                     "cannot access '{}' before initialization",

boa_parser/src/parser/statement/mod.rs

@@ -20,6 +20,7 @@ mod switch;
 mod throw;
 mod try_stm;
 mod variable;
+mod with;
 
 use self::{
     block::BlockStatement,
@@ -35,6 +36,7 @@ use self::{
     throw::ThrowStatement,
     try_stm::TryStatement,
     variable::VariableStatement,
+    with::WithStatement,
 };
 use crate::{
     lexer::{
@@ -124,6 +126,11 @@ where
         let tok = cursor.peek(0, interner).or_abrupt()?;
 
         match tok.kind() {
+            TokenKind::Keyword((Keyword::With, _)) => {
+                WithStatement::new(self.allow_yield, self.allow_await, self.allow_return)
+                    .parse(cursor, interner)
+                    .map(ast::Statement::from)
+            }
             TokenKind::Keyword((Keyword::If, _)) => {
                 IfStatement::new(self.allow_yield, self.allow_await, self.allow_return)
                     .parse(cursor, interner)

boa_parser/src/parser/statement/with/mod.rs

@@ -0,0 +1,89 @@
+//! With statement parsing.
+
+use crate::{
+    parser::{
+        cursor::Cursor, expression::Expression, statement::Statement, AllowAwait, AllowReturn,
+        AllowYield, ParseResult, TokenParser,
+    },
+    Error,
+};
+use boa_ast::{statement::With, Keyword, Punctuator};
+use boa_interner::Interner;
+use boa_profiler::Profiler;
+use std::io::Read;
+
+/// With statement parsing.
+///
+/// More information:
+///  - [MDN documentation][mdn]
+///  - [ECMAScript specification][spec]
+///
+/// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with
+/// [spec]: https://tc39.es/ecma262/#prod-WithStatement
+#[derive(Debug, Clone, Copy)]
+pub(in crate::parser::statement) struct WithStatement {
+    allow_yield: AllowYield,
+    allow_await: AllowAwait,
+    allow_return: AllowReturn,
+}
+
+impl WithStatement {
+    /// Creates a new `WithStatement` parser.
+    pub(in crate::parser::statement) fn new<Y, A, R>(
+        allow_yield: Y,
+        allow_await: A,
+        allow_return: R,
+    ) -> Self
+    where
+        Y: Into<AllowYield>,
+        A: Into<AllowAwait>,
+        R: Into<AllowReturn>,
+    {
+        Self {
+            allow_yield: allow_yield.into(),
+            allow_await: allow_await.into(),
+            allow_return: allow_return.into(),
+        }
+    }
+}
+
+impl<R> TokenParser<R> for WithStatement
+where
+    R: Read,
+{
+    type Output = With;
+
+    fn parse(self, cursor: &mut Cursor<R>, interner: &mut Interner) -> ParseResult<Self::Output> {
+        let _timer = Profiler::global().start_event("WithStatement", "Parsing");
+
+        let position = cursor
+            .expect((Keyword::With, false), "with statement", interner)?
+            .span()
+            .start();
+
+        // It is a Syntax Error if the source text matched by this production is contained in strict mode code.
+        if cursor.strict_mode() {
+            return Err(Error::general(
+                "with statement not allowed in strict mode",
+                position,
+            ));
+        }
+
+        cursor.expect(Punctuator::OpenParen, "with statement", interner)?;
+        let expression = Expression::new(None, true, self.allow_yield, self.allow_await)
+            .parse(cursor, interner)?;
+        let position = cursor
+            .expect(Punctuator::CloseParen, "with statement", interner)?
+            .span()
+            .end();
+        let statement = Statement::new(self.allow_yield, self.allow_await, self.allow_return)
+            .parse(cursor, interner)?;
+
+        // It is a Syntax Error if IsLabelledFunction(Statement) is true.
+        if statement.is_labelled_function() {
+            return Err(Error::wrong_labelled_function_declaration(position));
+        }
+
+        Ok(With::new(expression, statement))
+    }
+}