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[[HostDefined]] Refactor #3370

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[[HostDefined]] Refactor #3370

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aa8c75e
Refactor the `[[HostDefined]]` implementation.
johnyob Oct 9, 2023
72e5a2d
Update `[[HostDefined]]` example.
johnyob Oct 9, 2023
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89 changes: 35 additions & 54 deletions boa_engine/src/host_defined.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,97 +6,78 @@ use rustc_hash::FxHashMap;

use crate::object::NativeObject;

/// Map used to store the host defined objects.
#[doc(hidden)]
type HostDefinedMap = FxHashMap<TypeId, Box<dyn NativeObject>>;

/// This represents a `ECMASCript` specification \[`HostDefined`\] field.
///
/// This allows storing types which are mapped by their [`TypeId`].
#[derive(Default, Trace, Finalize)]
#[allow(missing_debug_implementations)]
pub struct HostDefined {
state: GcRefCell<HostDefinedMap>,
env: FxHashMap<TypeId, GcRefCell<Box<dyn NativeObject>>>,
}

#[allow(unsafe_op_in_unsafe_fn)]
unsafe fn downcast_boxed_native_object_unchecked<T: NativeObject>(
obj: Box<dyn NativeObject>,
) -> Box<T> {
let raw: *mut dyn NativeObject = Box::into_raw(obj);
Box::from_raw(raw as *mut T)
}

impl HostDefined {
/// Insert a type into the [`HostDefined`].
///
/// # Panics
///
/// Panics if [`HostDefined`] field is borrowed.
#[track_caller]
pub fn insert_default<T: NativeObject + Default>(&self) -> Option<Box<dyn NativeObject>> {
self.state
.borrow_mut()
.insert(TypeId::of::<T>(), Box::<T>::default())
pub fn insert_default<T: NativeObject + Default>(&mut self) -> Option<Box<T>> {
self.env
.insert(TypeId::of::<T>(), GcRefCell::new(Box::new(T::default())))
.map(|obj| unsafe { downcast_boxed_native_object_unchecked(obj.into_inner()) })
}

/// Insert a type into the [`HostDefined`].
///
/// # Panics
///
/// Panics if [`HostDefined`] field is borrowed.
#[track_caller]
pub fn insert<T: NativeObject>(&self, value: T) -> Option<Box<dyn NativeObject>> {
self.state
.borrow_mut()
.insert(TypeId::of::<T>(), Box::new(value))
pub fn insert<T: NativeObject>(&mut self, value: T) -> Option<Box<T>> {
self.env
.insert(TypeId::of::<T>(), GcRefCell::new(Box::new(value)))
.map(|obj| unsafe { downcast_boxed_native_object_unchecked(obj.into_inner()) })
}

/// Check if the [`HostDefined`] has type T.
///
/// # Panics
///
/// Panics if [`HostDefined`] field is borrowed mutably.
#[track_caller]
pub fn has<T: NativeObject>(&self) -> bool {
self.state.borrow().contains_key(&TypeId::of::<T>())
self.env.contains_key(&TypeId::of::<T>())
}

/// Remove type T from [`HostDefined`], if it exists.
///
/// Returns [`Some`] with the object if it exits, [`None`] otherwise.
///
/// # Panics
///
/// Panics if [`HostDefined`] field is borrowed.
#[track_caller]
pub fn remove<T: NativeObject>(&self) -> Option<Box<dyn NativeObject>> {
self.state.borrow_mut().remove(&TypeId::of::<T>())
pub fn remove<T: NativeObject>(&mut self) -> Option<Box<T>> {
self.env
.remove(&TypeId::of::<T>())
.map(|obj| unsafe { downcast_boxed_native_object_unchecked(obj.into_inner()) })
}

/// Get type T from [`HostDefined`], if it exits.
/// Get type T from [`HostDefined`], if it exists.
///
/// # Panics
///
/// Panics if [`HostDefined`] field is borrowed.
/// Panics if T's entry in [`HostDefined`] is mutably borrowed.
#[track_caller]
pub fn get<T: NativeObject>(&self) -> Option<GcRef<'_, T>> {
GcRef::try_map(self.state.borrow(), |state| {
state
.get(&TypeId::of::<T>())
.map(Box::as_ref)
.and_then(<dyn NativeObject>::downcast_ref::<T>)
})
let entry = self.env.get(&TypeId::of::<T>())?;

GcRef::try_map(entry.borrow(), |obj| obj.as_ref().downcast_ref::<T>())
}

/// Get type T from [`HostDefined`], if it exits.
/// Get type T from [`HostDefined`], if it exists.
///
/// # Panics
///
/// Panics if [`HostDefined`] field is borrowed.
/// Panics if T's entry in [`HostDefined`] is borrowed.
#[track_caller]
pub fn get_mut<T: NativeObject>(&self) -> Option<GcRefMut<'_, HostDefinedMap, T>> {
GcRefMut::try_map(
self.state.borrow_mut(),
|state: &mut FxHashMap<TypeId, Box<dyn NativeObject>>| {
state
.get_mut(&TypeId::of::<T>())
.map(Box::as_mut)
.and_then(<dyn NativeObject>::downcast_mut::<T>)
},
)
pub fn get_mut<T: NativeObject>(&self) -> Option<GcRefMut<'_, Box<dyn NativeObject>, T>> {
let entry = self.env.get(&TypeId::of::<T>())?;

GcRefMut::try_map(entry.borrow_mut(), |obj| obj.as_mut().downcast_mut::<T>())
}

/// Clears all the objects.
Expand All @@ -105,7 +86,7 @@ impl HostDefined {
///
/// Panics if [`HostDefined`] field is borrowed.
#[track_caller]
pub fn clear(&self) {
self.state.borrow_mut().clear();
pub fn clear(&mut self) {
self.env.clear();
}
}
6 changes: 3 additions & 3 deletions boa_engine/src/realm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,7 @@ struct Inner {
loaded_modules: GcRefCell<FxHashMap<JsString, Module>>,
host_classes: GcRefCell<FxHashMap<TypeId, StandardConstructor>>,

host_defined: HostDefined,
host_defined: GcRefCell<HostDefined>,
}

impl Realm {
Expand All @@ -86,7 +86,7 @@ impl Realm {
template_map: GcRefCell::default(),
loaded_modules: GcRefCell::default(),
host_classes: GcRefCell::default(),
host_defined: HostDefined::default(),
host_defined: GcRefCell::default(),
}),
};

Expand All @@ -107,7 +107,7 @@ impl Realm {
/// [spec]: https://tc39.es/ecma262/#table-realm-record-fields
#[inline]
#[must_use]
pub fn host_defined(&self) -> &HostDefined {
pub fn host_defined(&self) -> &GcRefCell<HostDefined> {
&self.inner.host_defined
}

Expand Down
40 changes: 23 additions & 17 deletions boa_examples/src/bin/host_defined.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -32,51 +32,54 @@ fn main() -> Result<(), JsError> {
// Get the realm from the context.
let realm = context.realm().clone();

// Get the [[HostDefined]] field from the realm.
let mut host_defined = realm.host_defined().borrow_mut();

// Insert a default CustomHostDefinedStruct.
realm
.host_defined()
.insert_default::<CustomHostDefinedStruct>();
host_defined.insert_default::<CustomHostDefinedStruct>();

{
assert!(realm.host_defined().has::<CustomHostDefinedStruct>());
assert!(host_defined.has::<CustomHostDefinedStruct>());

// Get the [[HostDefined]] field from the realm and downcast it to our concrete type.
let Some(host_defined) = realm.host_defined().get::<CustomHostDefinedStruct>() else {
let Some(custom_host_defined_struct) = host_defined.get::<CustomHostDefinedStruct>() else {
return Err(JsNativeError::typ()
.with_message("Realm does not have HostDefined field")
.into());
};

// Assert that the [[HostDefined]] field is in it's initial state.
assert_eq!(host_defined.counter, 0);
assert_eq!(custom_host_defined_struct.counter, 0);
}

// Insert another struct with state into [[HostDefined]] field.
realm
.host_defined()
.insert(AnotherCustomHostDefinedStruct::new(10));
host_defined.insert(AnotherCustomHostDefinedStruct::new(10));

{
assert!(realm.host_defined().has::<AnotherCustomHostDefinedStruct>());
assert!(host_defined.has::<AnotherCustomHostDefinedStruct>());

// Get the [[HostDefined]] field from the realm and downcast it to our concrete type.
let Some(host_defined) = realm.host_defined().get::<AnotherCustomHostDefinedStruct>()
let Some(another_custom_host_defined_struct) =
host_defined.get::<AnotherCustomHostDefinedStruct>()
else {
return Err(JsNativeError::typ()
.with_message("Realm does not have HostDefined field")
.into());
};

// Assert that the [[HostDefined]] field is in it's initial state.
assert_eq!(host_defined.counter, 10);
assert_eq!(another_custom_host_defined_struct.counter, 10);
}

// Remove a type from the [[HostDefined]] field.
assert!(realm
.host_defined()
assert!(host_defined
.remove::<AnotherCustomHostDefinedStruct>()
.is_some());

// We need to explicitly drop the borrow of the [[HostDefined]] field
// to avoid a double borrow when running the JavaScript code.
drop(host_defined);

// Create and register function for getting and setting the realm value.
//
// The funtion lives in the context's realm and has access to the host-defined field.
Expand All @@ -86,7 +89,7 @@ fn main() -> Result<(), JsError> {
NativeFunction::from_fn_ptr(|_, args, context| {
let value: usize = args.get_or_undefined(0).try_js_into(context)?;

let host_defined = context.realm().host_defined();
let host_defined = context.realm().host_defined().borrow_mut();
let Some(mut host_defined) = host_defined.get_mut::<CustomHostDefinedStruct>() else {
return Err(JsNativeError::typ()
.with_message("Realm does not have HostDefined field")
Expand All @@ -103,7 +106,7 @@ fn main() -> Result<(), JsError> {
js_string!("getRealmValue"),
0,
NativeFunction::from_fn_ptr(|_, _, context| {
let host_defined = context.realm().host_defined();
let host_defined = context.realm().host_defined().borrow_mut();
let Some(host_defined) = host_defined.get::<CustomHostDefinedStruct>() else {
return Err(JsNativeError::typ()
.with_message("Realm does not have HostDefined field")
Expand All @@ -122,7 +125,10 @@ fn main() -> Result<(), JsError> {
",
))?;

let Some(host_defined) = realm.host_defined().get::<CustomHostDefinedStruct>() else {
// Get the [[HostDefined]] field from the realm
let host_defined = realm.host_defined().borrow();

let Some(host_defined) = host_defined.get::<CustomHostDefinedStruct>() else {
return Err(JsNativeError::typ()
.with_message("Realm does not have HostDefined field")
.into());
Expand Down
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