Fix DataDescriptor Value to possibly be empty (#1419)

boa/src/object/gcobject.rs

@@ -534,12 +534,14 @@ impl GcObject {
             }
 
             Ok(AccessorDescriptor::new(get, set, attribute).into())
+        } else if let Some(v) = value {
+            Ok(DataDescriptor::new(v, attribute).into())
         } else {
-            Ok(DataDescriptor::new(value.unwrap_or_else(Value::undefined), attribute).into())
+            Ok(DataDescriptor::new_without_value(attribute).into())
         }
     }
 
-    /// Reeturn `true` if it is a native object and the native type is `T`.
+    /// Return `true` if it is a native object and the native type is `T`.
     ///
     /// # Panics
     ///

boa/src/object/internal_methods.rs

@@ -196,6 +196,7 @@ impl GcObject {
             }
 
             self.insert(key, desc);
+
             return true;
         };
 
@@ -234,8 +235,8 @@ impl GcObject {
                     return false;
                 }
 
-                let current = DataDescriptor::new(value, current.attributes());
-                self.insert(key, current);
+                self.insert(key, DataDescriptor::new(value, current.attributes()));
+
                 return true;
             }
             (PropertyDescriptor::Data(current), PropertyDescriptor::Data(desc)) => {
@@ -268,7 +269,22 @@ impl GcObject {
             }
         }
 
-        self.insert(key, desc);
+        match (&current, &desc) {
+            (PropertyDescriptor::Data(current_data), PropertyDescriptor::Data(desc_data)) => {
+                if desc_data.has_value() {
+                    self.insert(key, desc);
+                } else {
+                    self.insert(
+                        key,
+                        DataDescriptor::new(current_data.value.clone(), desc_data.attributes()),
+                    );
+                }
+            }
+            _ => {
+                self.insert(key, desc);
+            }
+        }
+
         true
     }
 

boa/src/property/mod.rs

@@ -36,6 +36,7 @@ pub use attribute::Attribute;
 pub struct DataDescriptor {
     pub(crate) value: Value,
     attributes: Attribute,
+    has_value: bool,
 }
 
 impl DataDescriptor {
@@ -48,6 +49,17 @@ impl DataDescriptor {
         Self {
             value: value.into(),
             attributes,
+            has_value: true,
+        }
+    }
+
+    /// Create a new `DataDescriptor` without a value.
+    #[inline]
+    pub fn new_without_value(attributes: Attribute) -> Self {
+        Self {
+            value: Value::undefined(),
+            attributes,
+            has_value: false,
         }
     }
 
@@ -57,6 +69,12 @@ impl DataDescriptor {
         self.value.clone()
     }
 
+    /// Check whether the data descriptor has a value.
+    #[inline]
+    pub fn has_value(&self) -> bool {
+        self.has_value
+    }
+
     /// Return the attributes of the descriptor.
     #[inline]
     pub fn attributes(&self) -> Attribute {