LibJS: Distinguish between omitted descriptor attributes and false ones

When calling Object.defineProperty, there is now a difference between
omitting a descriptor attribute and specifying that it is false. For
example, "{}" and "{ configurable: false }" will have different
attribute values.

8 files changed, 186 insertions, 83 deletions

diff --git a/Libraries/LibJS/AST.cpp b/Libraries/LibJS/AST.cpp
index 1aebc91944..1bb684d7ee 100644
--- a/Libraries/LibJS/AST.cpp
+++ b/Libraries/LibJS/AST.cpp
@@ -1304,7 +1304,7 @@ Value ObjectExpression::execute(Interpreter& interpreter) const
                 auto& obj_to_spread = key_result.as_object();
 
                 for (auto& it : obj_to_spread.shape().property_table_ordered()) {
-                    if (it.value.attributes & Attribute::Enumerable)
+                    if (it.value.attributes.is_enumerable())
                         object->define_property(it.key, obj_to_spread.get(it.key));
                 }
             } else if (key_result.is_string()) {
diff --git a/Libraries/LibJS/Runtime/IndexedProperties.cpp b/Libraries/LibJS/Runtime/IndexedProperties.cpp
index 5da0f570b6..3ef6f16166 100644
--- a/Libraries/LibJS/Runtime/IndexedProperties.cpp
+++ b/Libraries/LibJS/Runtime/IndexedProperties.cpp
@@ -47,7 +47,7 @@ Optional<ValueAndAttributes> SimpleIndexedPropertyStorage::get(u32 index) const
     return ValueAndAttributes { m_packed_elements[index], default_attributes };
 }
 
-void SimpleIndexedPropertyStorage::put(u32 index, Value value, u8 attributes)
+void SimpleIndexedPropertyStorage::put(u32 index, Value value, PropertyAttributes attributes)
 {
     ASSERT(attributes == default_attributes);
     ASSERT(index < SPARSE_ARRAY_THRESHOLD);
@@ -66,7 +66,7 @@ void SimpleIndexedPropertyStorage::remove(u32 index)
         m_packed_elements[index] = {};
 }
 
-void SimpleIndexedPropertyStorage::insert(u32 index, Value value, u8 attributes)
+void SimpleIndexedPropertyStorage::insert(u32 index, Value value, PropertyAttributes attributes)
 {
     ASSERT(attributes == default_attributes);
     ASSERT(index < SPARSE_ARRAY_THRESHOLD);
@@ -122,7 +122,7 @@ Optional<ValueAndAttributes> GenericIndexedPropertyStorage::get(u32 index) const
     return m_sparse_elements.get(index);
 }
 
-void GenericIndexedPropertyStorage::put(u32 index, Value value, u8 attributes)
+void GenericIndexedPropertyStorage::put(u32 index, Value value, PropertyAttributes attributes)
 {
     if (index >= m_array_size)
         m_array_size = index + 1;
@@ -151,7 +151,7 @@ void GenericIndexedPropertyStorage::remove(u32 index)
     }
 }
 
-void GenericIndexedPropertyStorage::insert(u32 index, Value value, u8 attributes)
+void GenericIndexedPropertyStorage::insert(u32 index, Value value, PropertyAttributes attributes)
 {
     if (index >= m_array_size) {
         put(index, value, attributes);
@@ -281,7 +281,7 @@ Optional<ValueAndAttributes> IndexedProperties::get(Object* this_object, u32 ind
     return result;
 }
 
-void IndexedProperties::put(Object* this_object, u32 index, Value value, u8 attributes, bool evaluate_accessors)
+void IndexedProperties::put(Object* this_object, u32 index, Value value, PropertyAttributes attributes, bool evaluate_accessors)
 {
     if (m_storage->is_simple_storage() && (index >= SPARSE_ARRAY_THRESHOLD || attributes != default_attributes))
         switch_to_generic_storage();
@@ -304,13 +304,13 @@ bool IndexedProperties::remove(u32 index)
     auto result = m_storage->get(index);
     if (!result.has_value())
         return true;
-    if (!(result.value().attributes & Attribute::Configurable))
+    if (!result.value().attributes.is_configurable())
         return false;
     m_storage->remove(index);
     return true;
 }
 
-void IndexedProperties::insert(u32 index, Value value, u8 attributes)
+void IndexedProperties::insert(u32 index, Value value, PropertyAttributes attributes)
 {
     if (m_storage->is_simple_storage() && (index >= SPARSE_ARRAY_THRESHOLD || attributes != default_attributes || array_like_size() == SPARSE_ARRAY_THRESHOLD))
         switch_to_generic_storage();
diff --git a/Libraries/LibJS/Runtime/IndexedProperties.h b/Libraries/LibJS/Runtime/IndexedProperties.h
index 9456a9dafe..916a7747c2 100644
--- a/Libraries/LibJS/Runtime/IndexedProperties.h
+++ b/Libraries/LibJS/Runtime/IndexedProperties.h
@@ -37,7 +37,7 @@ const u32 MIN_PACKED_RESIZE_AMOUNT = 20;
 
 struct ValueAndAttributes {
     Value value;
-    u8 attributes { default_attributes };
+    PropertyAttributes attributes { default_attributes };
 };
 
 class IndexedProperties;
@@ -50,10 +50,10 @@ public:
 
     virtual bool has_index(u32 index) const = 0;
     virtual Optional<ValueAndAttributes> get(u32 index) const = 0;
-    virtual void put(u32 index, Value value, u8 attributes = default_attributes) = 0;
+    virtual void put(u32 index, Value value, PropertyAttributes attributes = default_attributes) = 0;
     virtual void remove(u32 index) = 0;
 
-    virtual void insert(u32 index, Value value, u8 attributes = default_attributes) = 0;
+    virtual void insert(u32 index, Value value, PropertyAttributes attributes = default_attributes) = 0;
     virtual ValueAndAttributes take_first() = 0;
     virtual ValueAndAttributes take_last() = 0;
 
@@ -71,10 +71,10 @@ public:
 
     virtual bool has_index(u32 index) const override;
     virtual Optional<ValueAndAttributes> get(u32 index) const override;
-    virtual void put(u32 index, Value value, u8 attributes = default_attributes) override;
+    virtual void put(u32 index, Value value, PropertyAttributes attributes = default_attributes) override;
     virtual void remove(u32 index) override;
 
-    virtual void insert(u32 index, Value value, u8 attributes = default_attributes) override;
+    virtual void insert(u32 index, Value value, PropertyAttributes attributes = default_attributes) override;
     virtual ValueAndAttributes take_first() override;
     virtual ValueAndAttributes take_last() override;
 
@@ -98,10 +98,10 @@ public:
 
     virtual bool has_index(u32 index) const override;
     virtual Optional<ValueAndAttributes> get(u32 index) const override;
-    virtual void put(u32 index, Value value, u8 attributes = default_attributes) override;
+    virtual void put(u32 index, Value value, PropertyAttributes attributes = default_attributes) override;
     virtual void remove(u32 index) override;
 
-    virtual void insert(u32 index, Value value, u8 attributes = default_attributes) override;
+    virtual void insert(u32 index, Value value, PropertyAttributes attributes = default_attributes) override;
     virtual ValueAndAttributes take_first() override;
     virtual ValueAndAttributes take_last() override;
 
@@ -146,14 +146,14 @@ public:
 
     bool has_index(u32 index) const { return m_storage->has_index(index); }
     Optional<ValueAndAttributes> get(Object* this_object, u32 index, bool evaluate_accessors = true) const;
-    void put(Object* this_object, u32 index, Value value, u8 attributes = default_attributes, bool evaluate_accessors = true);
+    void put(Object* this_object, u32 index, Value value, PropertyAttributes attributes = default_attributes, bool evaluate_accessors = true);
     bool remove(u32 index);
 
-    void insert(u32 index, Value value, u8 attributes = default_attributes);
+    void insert(u32 index, Value value, PropertyAttributes attributes = default_attributes);
     ValueAndAttributes take_first(Object* this_object);
     ValueAndAttributes take_last(Object* this_object);
 
-    void append(Value value, u8 attributes = default_attributes) { put(nullptr, array_like_size(), value, attributes, false); }
+    void append(Value value, PropertyAttributes attributes = default_attributes) { put(nullptr, array_like_size(), value, attributes, false); }
     void append_all(Object* this_object, const IndexedProperties& properties, bool evaluate_accessors = true);
 
     IndexedPropertyIterator begin(bool skip_empty = true) const { return IndexedPropertyIterator(*this, 0, skip_empty); };
diff --git a/Libraries/LibJS/Runtime/Object.cpp b/Libraries/LibJS/Runtime/Object.cpp
index e62c68cfaa..2b3995f98a 100644
--- a/Libraries/LibJS/Runtime/Object.cpp
+++ b/Libraries/LibJS/Runtime/Object.cpp
@@ -123,7 +123,7 @@ Value Object::get_own_property(const Object& this_object, PropertyName property_
     return value_here;
 }
 
-Value Object::get_own_properties(const Object& this_object, GetOwnPropertyMode kind, u8 attributes) const
+Value Object::get_own_properties(const Object& this_object, GetOwnPropertyMode kind, PropertyAttributes attributes) const
 {
     auto* properties_array = Array::create(interpreter().global_object());
 
@@ -168,7 +168,7 @@ Value Object::get_own_properties(const Object& this_object, GetOwnPropertyMode k
     }
 
     for (auto& it : this_object.shape().property_table_ordered()) {
-        if (it.value.attributes & attributes) {
+        if (it.value.attributes.bits() & attributes.bits()) {
             size_t offset = it.value.offset + property_index;
 
             if (kind == GetOwnPropertyMode::Key) {
@@ -194,7 +194,7 @@ Value Object::get_own_properties(const Object& this_object, GetOwnPropertyMode k
 Value Object::get_own_property_descriptor(PropertyName property_name) const
 {
     Value value;
-    u8 attributes;
+    PropertyAttributes attributes;
 
     if (property_name.is_number()) {
         auto existing_value = m_indexed_properties.get(nullptr, property_name.as_number(), false);
@@ -214,12 +214,12 @@ Value Object::get_own_property_descriptor(PropertyName property_name) const
     }
 
     auto* descriptor = Object::create_empty(interpreter(), interpreter().global_object());
-    descriptor->define_property("enumerable", Value((attributes & Attribute::Enumerable) != 0));
-    descriptor->define_property("configurable", Value((attributes & Attribute::Configurable) != 0));
+    descriptor->define_property("enumerable", Value(attributes.is_enumerable()));
+    descriptor->define_property("configurable", Value(attributes.is_configurable()));
     if (value.is_object() && value.as_object().is_native_property()) {
         auto result = call_native_property_getter(const_cast<Object*>(this), value);
         descriptor->define_property("value", result);
-        descriptor->define_property("writable", Value((attributes & Attribute::Writable) != 0));
+        descriptor->define_property("writable", Value(attributes.is_writable()));
     } else if (value.is_accessor()) {
         auto& pair = value.as_accessor();
         if (pair.getter())
@@ -228,7 +228,7 @@ Value Object::get_own_property_descriptor(PropertyName property_name) const
             descriptor->define_property("set", pair.setter());
     } else {
         descriptor->define_property("value", value.value_or(js_undefined()));
-        descriptor->define_property("writable", Value((attributes & Attribute::Writable) != 0));
+        descriptor->define_property("writable", Value(attributes.is_writable()));
     }
     return descriptor;
 }
@@ -242,13 +242,25 @@ void Object::set_shape(Shape& new_shape)
 bool Object::define_property(const FlyString& property_name, const Object& descriptor, bool throw_exceptions)
 {
     bool is_accessor_property = descriptor.has_property("get") || descriptor.has_property("set");
-    u8 configurable = descriptor.get("configurable").value_or(Value(false)).to_boolean() * Attribute::Configurable;
-    if (interpreter().exception())
-        return {};
-    u8 enumerable = descriptor.get("enumerable").value_or(Value(false)).to_boolean() * Attribute::Enumerable;
-    if (interpreter().exception())
-        return {};
-    u8 attributes = configurable | enumerable;
+    PropertyAttributes attributes;
+    if (descriptor.has_property("configurable")) {
+        if (interpreter().exception())
+            return false;
+        attributes.set_has_configurable();
+        if (descriptor.get("configurable").value_or(Value(false)).to_boolean())
+            attributes.set_configurable();
+        if (interpreter().exception())
+            return false;
+    }
+    if (descriptor.has_property("enumerable")) {
+        if (interpreter().exception())
+            return false;
+        attributes.set_has_enumerable();
+        if (descriptor.get("enumerable").value_or(Value(false)).to_boolean())
+            attributes.set_enumerable();
+        if (interpreter().exception())
+            return false;
+    }
 
     if (is_accessor_property) {
         if (descriptor.has_property("value") || descriptor.has_property("writable")) {
@@ -291,10 +303,17 @@ bool Object::define_property(const FlyString& property_name, const Object& descr
     auto value = descriptor.get("value");
     if (interpreter().exception())
         return {};
-    u8 writable = descriptor.get("writable").value_or(Value(false)).to_boolean() * Attribute::Writable;
+    if (descriptor.has_property("writable")) {
+        if (interpreter().exception())
+            return false;
+        attributes.set_has_writable();
+        if (descriptor.get("writable").value_or(Value(false)).to_boolean())
+            attributes.set_writable();
+        if (interpreter().exception())
+            return false;
+    }
     if (interpreter().exception())
         return {};
-    attributes |= writable;
 
     dbg() << "Defining new property " << property_name << " with data descriptor { attributes=" << attributes
           << ", value=" << (value.is_empty() ? "<empty>" : value.to_string_without_side_effects()) << " }";
@@ -302,7 +321,7 @@ bool Object::define_property(const FlyString& property_name, const Object& descr
     return define_property(property_name, value, attributes, throw_exceptions);
 }
 
-bool Object::define_property(PropertyName property_name, Value value, u8 attributes, bool throw_exceptions)
+bool Object::define_property(PropertyName property_name, Value value, PropertyAttributes attributes, bool throw_exceptions)
 {
     if (property_name.is_number())
         return put_own_property_by_index(*this, property_name.as_number(), value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
@@ -313,7 +332,7 @@ bool Object::define_property(PropertyName property_name, Value value, u8 attribu
     return put_own_property(*this, property_name.as_string(), value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
 }
 
-bool Object::put_own_property(Object& this_object, const FlyString& property_name, Value value, u8 attributes, PutOwnPropertyMode mode, bool throw_exceptions)
+bool Object::put_own_property(Object& this_object, const FlyString& property_name, Value value, PropertyAttributes attributes, PutOwnPropertyMode mode, bool throw_exceptions)
 {
     ASSERT(!(mode == PutOwnPropertyMode::Put && value.is_accessor()));
 
@@ -327,9 +346,9 @@ bool Object::put_own_property(Object& this_object, const FlyString& property_nam
     if (value.is_accessor()) {
         auto& accessor = value.as_accessor();
         if (accessor.getter())
-            attributes |= Attribute::HasGet;
+            attributes.set_has_getter();
         if (accessor.setter())
-            attributes |= Attribute::HasSet;
+            attributes.set_has_setter();
     }
 
     auto metadata = shape().lookup(property_name);
@@ -352,7 +371,7 @@ bool Object::put_own_property(Object& this_object, const FlyString& property_nam
         ASSERT(metadata.has_value());
     }
 
-    if (!new_property && mode == PutOwnPropertyMode::DefineProperty && !(metadata.value().attributes & Attribute::Configurable) && attributes != metadata.value().attributes) {
+    if (!new_property && mode == PutOwnPropertyMode::DefineProperty && !metadata.value().attributes.is_configurable() && attributes != metadata.value().attributes) {
         dbg() << "Disallow reconfig of non-configurable property";
         if (throw_exceptions)
             interpreter().throw_exception<TypeError>(String::format("Cannot change attributes of non-configurable property '%s'", property_name.characters()));
@@ -371,7 +390,7 @@ bool Object::put_own_property(Object& this_object, const FlyString& property_nam
     }
 
     auto value_here = m_storage[metadata.value().offset];
-    if (!new_property && mode == PutOwnPropertyMode::Put && !value_here.is_accessor() && !(metadata.value().attributes & Attribute::Writable)) {
+    if (!new_property && mode == PutOwnPropertyMode::Put && !value_here.is_accessor() && !metadata.value().attributes.is_writable()) {
         dbg() << "Disallow write to non-writable property";
         return false;
     }
@@ -387,7 +406,7 @@ bool Object::put_own_property(Object& this_object, const FlyString& property_nam
     return true;
 }
 
-bool Object::put_own_property_by_index(Object& this_object, u32 property_index, Value value, u8 attributes, PutOwnPropertyMode mode, bool throw_exceptions)
+bool Object::put_own_property_by_index(Object& this_object, u32 property_index, Value value, PropertyAttributes attributes, PutOwnPropertyMode mode, bool throw_exceptions)
 {
     ASSERT(!(mode == PutOwnPropertyMode::Put && value.is_accessor()));
 
@@ -401,16 +420,16 @@ bool Object::put_own_property_by_index(Object& this_object, u32 property_index,
     if (value.is_accessor()) {
         auto& accessor = value.as_accessor();
         if (accessor.getter())
-            attributes |= Attribute::HasGet;
+            attributes.set_has_getter();
         if (accessor.setter())
-            attributes |= Attribute::HasSet;
+            attributes.set_has_setter();
     }
 
     auto existing_property = m_indexed_properties.get(nullptr, property_index, false);
     auto new_property = !existing_property.has_value();
-    auto existing_attributes = new_property ? 0 : existing_property.value().attributes;
+    PropertyAttributes existing_attributes = new_property ? 0 : existing_property.value().attributes;
 
-    if (!new_property && mode == PutOwnPropertyMode::DefineProperty && !(existing_attributes & Attribute::Configurable) && attributes != existing_attributes) {
+    if (!new_property && mode == PutOwnPropertyMode::DefineProperty && !existing_attributes.is_configurable() && attributes != existing_attributes) {
         dbg() << "Disallow reconfig of non-configurable property";
         if (throw_exceptions)
             interpreter().throw_exception<TypeError>(String::format("Cannot change attributes of non-configurable property %d", property_index));
@@ -418,7 +437,7 @@ bool Object::put_own_property_by_index(Object& this_object, u32 property_index,
     }
 
     auto value_here = new_property ? Value() : existing_property.value().value;
-    if (!new_property && mode == PutOwnPropertyMode::Put && !value_here.is_accessor() && !(existing_attributes & Attribute::Writable)) {
+    if (!new_property && mode == PutOwnPropertyMode::Put && !value_here.is_accessor() && !existing_attributes.is_writable()) {
         dbg() << "Disallow write to non-writable property";
         return false;
     }
@@ -442,7 +461,7 @@ Value Object::delete_property(PropertyName property_name)
     auto metadata = shape().lookup(property_name.as_string());
     if (!metadata.has_value())
         return Value(true);
-    if (!(metadata.value().attributes & Attribute::Configurable))
+    if (!metadata.value().attributes.is_configurable())
         return Value(false);
 
     size_t deleted_offset = metadata.value().offset;
@@ -565,7 +584,7 @@ bool Object::put(PropertyName property_name, Value value)
     return put_own_property(*this, property_string, value, default_attributes, PutOwnPropertyMode::Put);
 }
 
-bool Object::define_native_function(const FlyString& property_name, AK::Function<Value(Interpreter&)> native_function, i32 length, u8 attribute)
+bool Object::define_native_function(const FlyString& property_name, AK::Function<Value(Interpreter&)> native_function, i32 length, PropertyAttributes attribute)
 {
     auto* function = NativeFunction::create(interpreter(), interpreter().global_object(), property_name, move(native_function));
     function->define_property("length", Value(length), Attribute::Configurable);
@@ -573,7 +592,7 @@ bool Object::define_native_function(const FlyString& property_name, AK::Function
     return define_property(property_name, function, attribute);
 }
 
-bool Object::define_native_property(const FlyString& property_name, AK::Function<Value(Interpreter&)> getter, AK::Function<void(Interpreter&, Value)> setter, u8 attribute)
+bool Object::define_native_property(const FlyString& property_name, AK::Function<Value(Interpreter&)> getter, AK::Function<void(Interpreter&, Value)> setter, PropertyAttributes attribute)
 {
     return define_property(property_name, heap().allocate<NativeProperty>(move(getter), move(setter)), attribute);
 }
diff --git a/Libraries/LibJS/Runtime/Object.h b/Libraries/LibJS/Runtime/Object.h
index 3263b225ad..f39d816c08 100644
--- a/Libraries/LibJS/Runtime/Object.h
+++ b/Libraries/LibJS/Runtime/Object.h
@@ -68,14 +68,14 @@ public:
     bool put(PropertyName, Value);
 
     Value get_own_property(const Object& this_object, PropertyName) const;
-    Value get_own_properties(const Object& this_object, GetOwnPropertyMode, u8 attributes = default_attributes) const;
+    Value get_own_properties(const Object& this_object, GetOwnPropertyMode, PropertyAttributes attributes = default_attributes) const;
     Value get_own_property_descriptor(PropertyName) const;
 
     bool define_property(const FlyString& property_name, const Object& descriptor, bool throw_exceptions = true);
-    bool define_property(PropertyName, Value value, u8 attributes = default_attributes, bool throw_exceptions = true);
+    bool define_property(PropertyName, Value value, PropertyAttributes attributes = default_attributes, bool throw_exceptions = true);
 
-    bool define_native_function(const FlyString& property_name, AK::Function<Value(Interpreter&)>, i32 length = 0, u8 attribute = default_attributes);
-    bool define_native_property(const FlyString& property_name, AK::Function<Value(Interpreter&)> getter, AK::Function<void(Interpreter&, Value)> setter, u8 attribute = default_attributes);
+    bool define_native_function(const FlyString& property_name, AK::Function<Value(Interpreter&)>, i32 length = 0, PropertyAttributes attributes = default_attributes);
+    bool define_native_property(const FlyString& property_name, AK::Function<Value(Interpreter&)> getter, AK::Function<void(Interpreter&, Value)> setter, PropertyAttributes attributes = default_attributes);
 
     Value delete_property(PropertyName);
 
@@ -116,8 +116,8 @@ public:
 private:
     virtual Value get_by_index(u32 property_index) const;
     virtual bool put_by_index(u32 property_index, Value);
-    bool put_own_property(Object& this_object, const FlyString& property_name, Value, u8 attributes, PutOwnPropertyMode = PutOwnPropertyMode::Put, bool throw_exceptions = true);
-    bool put_own_property_by_index(Object& this_object, u32 property_index, Value, u8 attributes, PutOwnPropertyMode = PutOwnPropertyMode::Put, bool throw_exceptions = true);
+    bool put_own_property(Object& this_object, const FlyString& property_name, Value, PropertyAttributes attributes, PutOwnPropertyMode = PutOwnPropertyMode::Put, bool throw_exceptions = true);
+    bool put_own_property_by_index(Object& this_object, u32 property_index, Value, PropertyAttributes attributes, PutOwnPropertyMode = PutOwnPropertyMode::Put, bool throw_exceptions = true);
 
     Value call_native_property_getter(Object* this_object, Value property) const;
     void call_native_property_setter(Object* this_object, Value property, Value) const;
diff --git a/Libraries/LibJS/Runtime/PropertyAttributes.h b/Libraries/LibJS/Runtime/PropertyAttributes.h
new file mode 100644
index 0000000000..d421182a8c
--- /dev/null
+++ b/Libraries/LibJS/Runtime/PropertyAttributes.h
@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2020, Matthew Olsson <matthewcolsson@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+namespace JS {
+
+struct Attribute {
+    enum {
+        Configurable = 1 << 0,
+        Enumerable = 1 << 1,
+        Writable = 1 << 2,
+        HasGetter = 1 << 3,
+        HasSetter = 1 << 4,
+        HasConfigurable = 1 << 5,
+        HasEnumerable = 1 << 6,
+        HasWritable = 1 << 7,
+    };
+};
+
+class PropertyAttributes {
+public:
+    PropertyAttributes(u8 bits = 0)
+    {
+        m_bits = bits;
+        if (bits & Attribute::Configurable)
+            m_bits |= Attribute::HasConfigurable;
+        if (bits & Attribute::Enumerable)
+            m_bits |= Attribute::HasEnumerable;
+        if (bits & Attribute::Writable)
+            m_bits |= Attribute::HasWritable;
+    }
+
+    bool is_empty() const { return !m_bits; }
+
+    bool has_configurable() const { return m_bits & Attribute::HasConfigurable; }
+    bool has_enumerable() const { return m_bits & Attribute::HasEnumerable; }
+    bool has_writable() const { return m_bits & Attribute::HasWritable; }
+    bool has_getter() const { return m_bits & Attribute::HasGetter; }
+    bool has_setter() const { return m_bits & Attribute::HasSetter; }
+
+    bool is_configurable() const { return m_bits & Attribute::Configurable; }
+    bool is_enumerable() const { return m_bits & Attribute::Enumerable; }
+    bool is_writable() const { return m_bits & Attribute::Writable; }
+
+    void set_has_configurable() { m_bits |= Attribute::HasConfigurable; }
+    void set_has_enumerable() { m_bits |= Attribute::HasEnumerable; }
+    void set_has_writable() { m_bits |= Attribute::HasWritable; }
+    void set_configurable() { m_bits |= Attribute::Configurable; }
+    void set_enumerable() { m_bits |= Attribute::Enumerable; }
+    void set_writable() { m_bits |= Attribute::Writable; }
+    void set_has_getter() { m_bits |= Attribute::HasGetter; }
+    void set_has_setter() { m_bits |= Attribute::HasSetter; }
+
+    bool operator==(const PropertyAttributes& other) const { return m_bits == other.m_bits; }
+    bool operator!=(const PropertyAttributes& other) const { return m_bits != other.m_bits; }
+
+    u8 bits() const { return m_bits; }
+
+private:
+    u8 m_bits;
+};
+
+const LogStream& operator<<(const LogStream& stream, const PropertyAttributes& attributes);
+
+const PropertyAttributes default_attributes = Attribute::Configurable | Attribute::Writable | Attribute::Enumerable;
+
+}
diff --git a/Libraries/LibJS/Runtime/Shape.cpp b/Libraries/LibJS/Runtime/Shape.cpp
index ef10ea8c51..989894ec5d 100644
--- a/Libraries/LibJS/Runtime/Shape.cpp
+++ b/Libraries/LibJS/Runtime/Shape.cpp
@@ -29,6 +29,11 @@
 
 namespace JS {
 
+const LogStream& operator<<(const LogStream& stream, const PropertyAttributes& attributes)
+{
+    return stream << attributes.bits();
+}
+
 Shape* Shape::create_unique_clone() const
 {
     auto* new_shape = heap().allocate<Shape>();
@@ -40,7 +45,7 @@ Shape* Shape::create_unique_clone() const
     return new_shape;
 }
 
-Shape* Shape::create_put_transition(const FlyString& property_name, u8 attributes)
+Shape* Shape::create_put_transition(const FlyString& property_name, PropertyAttributes attributes)
 {
     TransitionKey key { property_name, attributes };
     if (auto* existing_shape = m_forward_transitions.get(key).value_or(nullptr))
@@ -50,7 +55,7 @@ Shape* Shape::create_put_transition(const FlyString& property_name, u8 attribute
     return new_shape;
 }
 
-Shape* Shape::create_configure_transition(const FlyString& property_name, u8 attributes)
+Shape* Shape::create_configure_transition(const FlyString& property_name, PropertyAttributes attributes)
 {
     TransitionKey key { property_name, attributes };
     if (auto* existing_shape = m_forward_transitions.get(key).value_or(nullptr))
@@ -69,7 +74,7 @@ Shape::Shape()
 {
 }
 
-Shape::Shape(Shape* previous_shape, const FlyString& property_name, u8 attributes, TransitionType transition_type)
+Shape::Shape(Shape* previous_shape, const FlyString& property_name, PropertyAttributes attributes, TransitionType transition_type)
     : m_previous(previous_shape)
     , m_property_name(property_name)
     , m_attributes(attributes)
@@ -160,7 +165,7 @@ void Shape::ensure_property_table() const
     }
 }
 
-void Shape::add_property_to_unique_shape(const FlyString& property_name, u8 attributes)
+void Shape::add_property_to_unique_shape(const FlyString& property_name, PropertyAttributes attributes)
 {
     ASSERT(is_unique());
     ASSERT(m_property_table);
@@ -168,7 +173,7 @@ void Shape::add_property_to_unique_shape(const FlyString& property_name, u8 attr
     m_property_table->set(property_name, { m_property_table->size(), attributes });
 }
 
-void Shape::reconfigure_property_in_unique_shape(const FlyString& property_name, u8 attributes)
+void Shape::reconfigure_property_in_unique_shape(const FlyString& property_name, PropertyAttributes attributes)
 {
     ASSERT(is_unique());
     ASSERT(m_property_table);
diff --git a/Libraries/LibJS/Runtime/Shape.h b/Libraries/LibJS/Runtime/Shape.h
index ac19d775c7..60f59f09e4 100644
--- a/Libraries/LibJS/Runtime/Shape.h
+++ b/Libraries/LibJS/Runtime/Shape.h
@@ -31,35 +31,23 @@
 #include <AK/OwnPtr.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Runtime/Cell.h>
+#include <LibJS/Runtime/PropertyAttributes.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS {
 
-struct Attribute {
-    enum {
-        Configurable = 1 << 0,
-        Enumerable = 1 << 1,
-        Writable = 1 << 2,
-        HasGet = 1 << 3,
-        HasSet = 1 << 4,
-    };
-};
-
-const u8 default_attributes = Attribute::Configurable | Attribute::Writable | Attribute::Enumerable;
-
 struct PropertyMetadata {
     size_t offset { 0 };
-    u8 attributes { 0 };
+    PropertyAttributes attributes { 0 };
 };
 
 struct TransitionKey {
     FlyString property_name;
-    u8 attributes { 0 };
+    PropertyAttributes attributes { 0 };
 
     bool operator==(const TransitionKey& other) const
     {
-        return property_name == other.property_name
-            && attributes == other.attributes;
+        return property_name == other.property_name && attributes == other.attributes;
     }
 };
 
@@ -75,11 +63,11 @@ public:
     };
 
     Shape();
-    Shape(Shape* previous_shape, const FlyString& property_name, u8 attributes, TransitionType);
+    Shape(Shape* previous_shape, const FlyString& property_name, PropertyAttributes attributes, TransitionType);
     Shape(Shape* previous_shape, Object* new_prototype);
 
-    Shape* create_put_transition(const FlyString& name, u8 attributes);
-    Shape* create_configure_transition(const FlyString& name, u8 attributes);
+    Shape* create_put_transition(const FlyString& name, PropertyAttributes attributes);
+    Shape* create_configure_transition(const FlyString& name, PropertyAttributes attributes);
     Shape* create_prototype_transition(Object* new_prototype);
 
     bool is_unique() const { return m_unique; }
@@ -102,8 +90,8 @@ public:
     void set_prototype_without_transition(Object* new_prototype) { m_prototype = new_prototype; }
 
     void remove_property_from_unique_shape(const FlyString&, size_t offset);
-    void add_property_to_unique_shape(const FlyString&, u8 attributes);
-    void reconfigure_property_in_unique_shape(const FlyString& property_name, u8 attributes);
+    void add_property_to_unique_shape(const FlyString&, PropertyAttributes attributes);
+    void reconfigure_property_in_unique_shape(const FlyString& property_name, PropertyAttributes attributes);
 
 private:
     virtual const char* class_name() const override { return "Shape"; }
@@ -116,7 +104,7 @@ private:
     HashMap<TransitionKey, Shape*> m_forward_transitions;
     Shape* m_previous { nullptr };
     FlyString m_property_name;
-    u8 m_attributes { 0 };
+    PropertyAttributes m_attributes { 0 };
     bool m_unique { false };
     Object* m_prototype { nullptr };
     TransitionType m_transition_type { TransitionType::Invalid };
@@ -128,6 +116,6 @@ template<>
 struct AK::Traits<JS::TransitionKey> : public GenericTraits<JS::TransitionKey> {
     static unsigned hash(const JS::TransitionKey& key)
     {
-        return pair_int_hash(int_hash(key.attributes), key.property_name.hash());
+        return pair_int_hash(key.attributes.bits(), key.property_name.hash());
     }
 };