Implement Classes (#1976)

This Pull Request fixes/closes #337.

It changes the following:

- Implement class declaration parsing.
- Implement class expression parsing.
- Implement class execution.

There are still some features like `super` missing and there are some early errors that are not implemented yet. But I think it makes sense to merge this, as we can branch out the missing features from here.

boa_engine/src/object/jsobject.rs

@@ -10,6 +10,7 @@ use crate::{
     Context, JsResult, JsValue,
 };
 use boa_gc::{self, Finalize, Gc, Trace};
+use rustc_hash::FxHashMap;
 use std::{
     cell::RefCell,
     collections::HashMap,
@@ -51,12 +52,28 @@ impl JsObject {
     /// internal slots from the `data` provided.
     #[inline]
     pub fn from_proto_and_data<O: Into<Option<Self>>>(prototype: O, data: ObjectData) -> Self {
-        Self::from_object(Object {
-            data,
-            prototype: prototype.into(),
-            extensible: true,
-            properties: PropertyMap::default(),
-        })
+        let prototype: Option<Self> = prototype.into();
+        if let Some(prototype) = prototype {
+            let private = {
+                let prototype_b = prototype.borrow();
+                prototype_b.private_elements.clone()
+            };
+            Self::from_object(Object {
+                data,
+                prototype: Some(prototype),
+                extensible: true,
+                properties: PropertyMap::default(),
+                private_elements: private,
+            })
+        } else {
+            Self::from_object(Object {
+                data,
+                prototype: None,
+                extensible: true,
+                properties: PropertyMap::default(),
+                private_elements: FxHashMap::default(),
+            })
+        }
     }
 
     /// Immutably borrows the `Object`.

boa_engine/src/object/mod.rs

@@ -45,6 +45,8 @@ use crate::{
     Context, JsBigInt, JsResult, JsString, JsSymbol, JsValue,
 };
 use boa_gc::{Finalize, Trace};
+use boa_interner::Sym;
+use rustc_hash::FxHashMap;
 use std::{
     any::Any,
     fmt::{self, Debug, Display},
@@ -106,6 +108,18 @@ pub struct Object {
     prototype: JsPrototype,
     /// Whether it can have new properties added to it.
     extensible: bool,
+    /// The `[[PrivateElements]]` internal slot.
+    private_elements: FxHashMap<Sym, PrivateElement>,
+}
+
+/// The representation of private object elements.
+#[derive(Clone, Debug, Trace, Finalize)]
+pub(crate) enum PrivateElement {
+    Value(JsValue),
+    Accessor {
+        getter: Option<JsObject>,
+        setter: Option<JsObject>,
+    },
 }
 
 /// Defines the kind of an object and its internal methods
@@ -459,6 +473,7 @@ impl Default for Object {
             properties: PropertyMap::default(),
             prototype: None,
             extensible: true,
+            private_elements: FxHashMap::default(),
         }
     }
 }
@@ -1219,6 +1234,62 @@ impl Object {
     pub(crate) fn remove(&mut self, key: &PropertyKey) -> Option<PropertyDescriptor> {
         self.properties.remove(key)
     }
+
+    /// Get a private element.
+    #[inline]
+    pub(crate) fn get_private_element(&self, name: Sym) -> Option<&PrivateElement> {
+        self.private_elements.get(&name)
+    }
+
+    /// Set a private element.
+    #[inline]
+    pub(crate) fn set_private_element(&mut self, name: Sym, value: PrivateElement) {
+        self.private_elements.insert(name, value);
+    }
+
+    /// Set a private setter.
+    #[inline]
+    pub(crate) fn set_private_element_setter(&mut self, name: Sym, setter: JsObject) {
+        match self.private_elements.get_mut(&name) {
+            Some(PrivateElement::Accessor {
+                getter: _,
+                setter: s,
+            }) => {
+                *s = Some(setter);
+            }
+            _ => {
+                self.private_elements.insert(
+                    name,
+                    PrivateElement::Accessor {
+                        getter: None,
+                        setter: Some(setter),
+                    },
+                );
+            }
+        }
+    }
+
+    /// Set a private getter.
+    #[inline]
+    pub(crate) fn set_private_element_getter(&mut self, name: Sym, getter: JsObject) {
+        match self.private_elements.get_mut(&name) {
+            Some(PrivateElement::Accessor {
+                getter: g,
+                setter: _,
+            }) => {
+                *g = Some(getter);
+            }
+            _ => {
+                self.private_elements.insert(
+                    name,
+                    PrivateElement::Accessor {
+                        getter: Some(getter),
+                        setter: None,
+                    },
+                );
+            }
+        }
+    }
 }
 
 /// The functions binding.