Implement type safe root object shape

boa_engine/benches/full.rs

@@ -1,7 +1,7 @@
 //! Benchmarks of the whole execution engine in Boa.
 
 use boa_engine::{
-    context::DefaultHooks, object::shape::SharedShape, optimizer::OptimizerOptions, realm::Realm,
+    context::DefaultHooks, object::shape::RootShape, optimizer::OptimizerOptions, realm::Realm,
     Context, Source,
 };
 use criterion::{criterion_group, criterion_main, Criterion};
@@ -16,7 +16,7 @@ static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
 
 fn create_realm(c: &mut Criterion) {
     c.bench_function("Create Realm", move |b| {
-        let root_shape = SharedShape::root();
+        let root_shape = RootShape::default();
         b.iter(|| Realm::create(&DefaultHooks, &root_shape))
     });
 }

boa_engine/src/builtins/weak/weak_ref.rs

@@ -80,9 +80,11 @@ impl BuiltInConstructor for WeakRef {
 
         // 3. Let weakRef be ? OrdinaryCreateFromConstructor(NewTarget, "%WeakRef.prototype%", « [[WeakRefTarget]] »).
         // 5. Set weakRef.[[WeakRefTarget]] to target.
+        let prototype =
+            get_prototype_from_constructor(new_target, StandardConstructors::weak_ref, context)?;
         let weak_ref = JsObject::from_proto_and_data_with_shared_shape(
             context.root_shape(),
-            get_prototype_from_constructor(new_target, StandardConstructors::weak_ref, context)?,
+            prototype,
             ObjectData::weak_ref(WeakGc::new(target.inner())),
         );
 

boa_engine/src/builtins/weak_map/mod.rs

@@ -82,9 +82,11 @@ impl BuiltInConstructor for WeakMap {
 
         // 2. Let map be ? OrdinaryCreateFromConstructor(NewTarget, "%WeakMap.prototype%", « [[WeakMapData]] »).
         // 3. Set map.[[WeakMapData]] to a new empty List.
+        let prototype =
+            get_prototype_from_constructor(new_target, StandardConstructors::weak_map, context)?;
         let map = JsObject::from_proto_and_data_with_shared_shape(
             context.root_shape(),
-            get_prototype_from_constructor(new_target, StandardConstructors::weak_map, context)?,
+            prototype,
             ObjectData::weak_map(boa_gc::WeakMap::new()),
         );
 

boa_engine/src/builtins/weak_set/mod.rs

@@ -78,9 +78,11 @@ impl BuiltInConstructor for WeakSet {
 
         // 2. Let set be ? OrdinaryCreateFromConstructor(NewTarget, "%WeakSet.prototype%", « [[WeakSetData]] »).
         // 3. Set set.[[WeakSetData]] to a new empty List.
+        let prototype =
+            get_prototype_from_constructor(new_target, StandardConstructors::weak_set, context)?;
         let weak_set = JsObject::from_proto_and_data_with_shared_shape(
             context.root_shape(),
-            get_prototype_from_constructor(new_target, StandardConstructors::weak_set, context)?,
+            prototype,
             ObjectData::weak_set(WeakMap::new()),
         );
 

boa_engine/src/context/intrinsics.rs

@@ -5,7 +5,7 @@ use boa_gc::{Finalize, Trace};
 use crate::{
     builtins::{iterable::IteratorPrototypes, uri::UriFunctions},
     object::{
-        shape::shared_shape::{template::ObjectTemplate, SharedShape},
+        shape::{shared_shape::template::ObjectTemplate, RootShape},
         JsFunction, JsObject, ObjectData, CONSTRUCTOR, PROTOTYPE,
     },
     property::{Attribute, PropertyKey},
@@ -27,7 +27,7 @@ pub struct Intrinsics {
 }
 
 impl Intrinsics {
-    pub(crate) fn new(root_shape: &SharedShape) -> Self {
+    pub(crate) fn new(root_shape: &RootShape) -> Self {
         let constructors = StandardConstructors::default();
         let templates = ObjectTemplates::new(root_shape, &constructors);
 
@@ -1004,7 +1004,9 @@ pub(crate) struct ObjectTemplates {
 }
 
 impl ObjectTemplates {
-    pub(crate) fn new(root_shape: &SharedShape, constructors: &StandardConstructors) -> Self {
+    pub(crate) fn new(root_shape: &RootShape, constructors: &StandardConstructors) -> Self {
+        let root_shape = root_shape.shape();
+
         // pre-initialize used shapes.
         let ordinary_object =
             ObjectTemplate::with_prototype(root_shape, constructors.object().prototype());

boa_engine/src/context/mod.rs

@@ -23,7 +23,7 @@ use crate::{
     job::{JobQueue, NativeJob, SimpleJobQueue},
     module::{ModuleLoader, SimpleModuleLoader},
     native_function::NativeFunction,
-    object::{shape::SharedShape, FunctionObjectBuilder, JsObject},
+    object::{shape::RootShape, FunctionObjectBuilder, JsObject},
     optimizer::{Optimizer, OptimizerOptions, OptimizerStatistics},
     property::{Attribute, PropertyDescriptor, PropertyKey},
     realm::Realm,
@@ -109,7 +109,7 @@ pub struct Context<'host> {
     module_loader: MaybeShared<'host, dyn ModuleLoader>,
 
     optimizer_options: OptimizerOptions,
-    root_shape: SharedShape,
+    root_shape: RootShape,
 
     /// Unique identifier for each parser instance used during the context lifetime.
     parser_identifier: u32,
@@ -496,8 +496,10 @@ impl<'host> Context<'host> {
         std::mem::replace(&mut self.realm, realm)
     }
 
-    pub(crate) fn root_shape(&self) -> SharedShape {
-        self.root_shape.clone()
+    /// Get the [`RootShape`].
+    #[inline]
+    pub const fn root_shape(&self) -> &RootShape {
+        &self.root_shape
     }
 
     /// Gets the host hooks.
@@ -916,7 +918,7 @@ impl<'icu, 'hooks, 'queue, 'module> ContextBuilder<'icu, 'hooks, 'queue, 'module
         'queue: 'host,
         'module: 'host,
     {
-        let root_shape = SharedShape::root();
+        let root_shape = RootShape::default();
 
         let host_hooks = self.host_hooks.unwrap_or_else(|| {
             let hooks: &dyn HostHooks = &DefaultHooks;

boa_engine/src/object/jsobject.rs

@@ -4,7 +4,7 @@
 
 use super::{
     internal_methods::{InternalObjectMethods, ARRAY_EXOTIC_INTERNAL_METHODS},
-    shape::{shared_shape::SharedShape, Shape},
+    shape::RootShape,
     JsPrototype, NativeObject, Object, PropertyMap,
 };
 use crate::{
@@ -127,7 +127,7 @@ impl JsObject {
     ///
     /// [`OrdinaryObjectCreate`]: https://tc39.es/ecma262/#sec-ordinaryobjectcreate
     pub(crate) fn from_proto_and_data_with_shared_shape<O: Into<Option<Self>>>(
-        root_shape: SharedShape,
+        root_shape: &RootShape,
         prototype: O,
         data: ObjectData,
     ) -> Self {
@@ -136,7 +136,7 @@ impl JsObject {
                 object: GcRefCell::new(Object {
                     kind: data.kind,
                     properties: PropertyMap::from_prototype_with_shared_shape(
-                        Shape::shared(root_shape),
+                        root_shape,
                         prototype.into(),
                     ),
                     extensible: true,

boa_engine/src/object/property_map.rs

@@ -3,7 +3,7 @@ use super::{
         property_table::PropertyTableInner,
         shared_shape::TransitionKey,
         slot::{Slot, SlotAttributes},
-        ChangeTransitionAction, Shape, UniqueShape,
+        ChangeTransitionAction, RootShape, Shape, UniqueShape,
     },
     JsPrototype, ObjectStorage, PropertyDescriptor, PropertyKey,
 };
@@ -252,11 +252,14 @@ impl PropertyMap {
     /// Construct a [`PropertyMap`] from with the given prototype with a shared shape [`Shape`].
     #[must_use]
     #[inline]
-    pub fn from_prototype_with_shared_shape(mut root_shape: Shape, prototype: JsPrototype) -> Self {
-        root_shape = root_shape.change_prototype_transition(prototype);
+    pub fn from_prototype_with_shared_shape(
+        root_shape: &RootShape,
+        prototype: JsPrototype,
+    ) -> Self {
+        let shape = root_shape.shape().change_prototype_transition(prototype);
         Self {
             indexed_properties: IndexedProperties::default(),
-            shape: root_shape,
+            shape: Shape::shared(shape),
             storage: Vec::default(),
         }
     }

boa_engine/src/object/shape/mod.rs

@@ -1,10 +1,12 @@
 //! Implements object shapes.
 
 pub(crate) mod property_table;
+mod root_shape;
 pub(crate) mod shared_shape;
 pub(crate) mod slot;
 pub(crate) mod unique_shape;
 
+pub use root_shape::RootShape;
 pub use shared_shape::SharedShape;
 pub(crate) use unique_shape::UniqueShape;
 

boa_engine/src/object/shape/root_shape.rs

@@ -0,0 +1,26 @@
+use boa_macros::{Finalize, Trace};
+
+use super::SharedShape;
+
+/// Represent the root shape that [`SharedShape`] transitions start from.
+///
+/// This is a wrapper around [`SharedShape`] that ensures that the shape the root shape.
+#[derive(Debug, Clone, Trace, Finalize)]
+pub struct RootShape {
+    shape: SharedShape,
+}
+
+impl Default for RootShape {
+    fn default() -> Self {
+        Self {
+            shape: SharedShape::root(),
+        }
+    }
+}
+
+impl RootShape {
+    /// Gets the inner [`SharedShape`].
+    pub(crate) const fn shape(&self) -> &SharedShape {
+        &self.shape
+    }
+}

boa_engine/src/object/shape/shared_shape/mod.rs

@@ -174,7 +174,7 @@ impl SharedShape {
 
     /// Create a root [`SharedShape`].
     #[must_use]
-    pub fn root() -> Self {
+    pub(crate) fn root() -> Self {
         Self::new(Inner {
             forward_transitions: ForwardTransition::default(),
             prototype: None,

boa_engine/src/realm.rs

@@ -10,7 +10,7 @@ use crate::{
     context::{intrinsics::Intrinsics, HostHooks},
     environments::DeclarativeEnvironment,
     module::Module,
-    object::{shape::shared_shape::SharedShape, JsObject},
+    object::{shape::RootShape, JsObject},
     JsString,
 };
 use boa_gc::{Finalize, Gc, GcRefCell, Trace};
@@ -57,7 +57,7 @@ struct Inner {
 impl Realm {
     /// Create a new Realm.
     #[inline]
-    pub fn create(hooks: &dyn HostHooks, root_shape: &SharedShape) -> Self {
+    pub fn create(hooks: &dyn HostHooks, root_shape: &RootShape) -> Self {
         let _timer = Profiler::global().start_event("Realm::create", "realm");
 
         let intrinsics = Intrinsics::new(root_shape);