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LibJS: Support array holes, encoded as empty JS::Value

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This patch adds a new kind of JS::Value, the empty value.
It's what you get when you do JSValue() (or most commonly, {} in C++.)

An empty Value signifies the absence of a value, and should never be
visible to JavaScript itself. As of right now, it's used for array
holes and as a return value when an exception has been thrown and we
just want to unwind.

This patch is a bit of a mess as I had to fix a whole bunch of code
that was relying on JSValue() being undefined, etc.
This commit is contained in:
Andreas Kling 2020-04-06 20:24:45 +02:00
parent 5495f06af5
commit bdffc9e7fb
9 changed files with 102 additions and 35 deletions
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18
Libraries/LibJS/Runtime/Object.cpp
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@ -77,6 +77,7 @@ Optional<Value> Object::get_own_property(const Object& this_object, const FlyStr
return {};
auto value_here = m_storage[metadata.value().offset];
ASSERT(!value_here.is_empty());
if (value_here.is_object() && value_here.as_object().is_native_property()) {
auto& native_property = static_cast<const NativeProperty&>(value_here.as_object());
auto& interpreter = const_cast<Object*>(this)->interpreter();
@ -126,8 +127,12 @@ Optional<Value> Object::get_by_index(i32 property_index) const
const Object* object = this;
while (object) {
if (static_cast<size_t>(property_index) < object->m_elements.size())
return object->m_elements[property_index];
if (static_cast<size_t>(property_index) < object->m_elements.size()) {
auto value = object->m_elements[property_index];
if (value.is_empty())
return {};
return value;
}
object = object->prototype();
}
return {};
@ -159,6 +164,7 @@ Optional<Value> Object::get(PropertyName property_name) const
void Object::put_by_index(i32 property_index, Value value)
{
ASSERT(!value.is_empty());
if (property_index < 0)
return put(String::number(property_index), value);
// FIXME: Implement some kind of sparse storage for arrays with huge indices.
@ -169,6 +175,7 @@ void Object::put_by_index(i32 property_index, Value value)
void Object::put(const FlyString& property_name, Value value)
{
ASSERT(!value.is_empty());
bool ok;
i32 property_index = property_name.to_int(ok);
if (ok && property_index >= 0)
@ -231,8 +238,11 @@ bool Object::has_own_property(const FlyString& property_name) const
{
bool ok;
i32 property_index = property_name.to_int(ok);
if (ok && property_index >= 0)
return static_cast<size_t>(property_index) < m_elements.size();
if (ok && property_index >= 0) {
if (static_cast<size_t>(property_index) >= m_elements.size())
return false;
return !m_elements[property_index].is_empty();
}
return shape().lookup(property_name).has_value();
}