LibJS: Automatically & lazily coerce PropertyNames into numbers

This commit expands on 5eef07d232 by
automatically trying to coerce Type::String PropertyNames into numbers
when a caller checks if the PropertyName is_number/is_string.
This has several benefits:
 - We no longer have to duplicate the number coercion code to every
   function that accepts a PropertyNumber. (Or more likely, forget to.)
 - This keeps the lazy nature of only doing the coercion when and if
   there is a semantic difference to the different PropertyName types,
   which means this shouldnt cause any performance drop.
 - Since this coercion changes the state of the PropertyName itself the
   result is essentially cached and can speed up any repeat uses of the
   same PropertyName instance.

Userland/Libraries/LibJS/Runtime/Object.cpp

@@ -196,11 +196,6 @@ bool Object::set_integrity_level(IntegrityLevel level)
     case IntegrityLevel::Sealed:
         for (auto& key : keys) {
             auto property_name = PropertyName::from_value(global_object(), key);
-            if (property_name.is_string() && property_name.string_may_be_number()) {
-                i32 property_index = property_name.as_string().to_int().value_or(-1);
-                if (property_index >= 0)
-                    property_name = property_index;
-            }
             update_property(property_name, ~Attribute::Configurable);
             if (vm.exception())
                 return {};
@@ -209,11 +204,6 @@ bool Object::set_integrity_level(IntegrityLevel level)
     case IntegrityLevel::Frozen:
         for (auto& key : keys) {
             auto property_name = PropertyName::from_value(global_object(), key);
-            if (property_name.is_string() && property_name.string_may_be_number()) {
-                i32 property_index = property_name.as_string().to_int().value_or(-1);
-                if (property_index >= 0)
-                    property_name = property_index;
-            }
             auto property_descriptor = get_own_property_descriptor(property_name);
             if (!property_descriptor.has_value())
                 continue;
@@ -395,11 +385,6 @@ Optional<PropertyDescriptor> Object::get_own_property_descriptor(const PropertyN
         value = existing_value.value().value;
         attributes = existing_value.value().attributes;
     } else {
-        if (property_name.is_string() && property_name.string_may_be_number()) {
-            i32 property_index = property_name.as_string().to_int().value_or(-1);
-            if (property_index >= 0)
-                return get_own_property_descriptor(property_index);
-        }
         auto metadata = shape().lookup(property_name.to_string_or_symbol());
         if (!metadata.has_value())
             return {};
@@ -545,11 +530,6 @@ bool Object::define_property(const PropertyName& property_name, Value value, Pro
     if (property_name.is_number())
         return put_own_property_by_index(property_name.as_number(), value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
 
-    if (property_name.is_string() && property_name.string_may_be_number()) {
-        i32 property_index = property_name.as_string().to_int().value_or(-1);
-        if (property_index >= 0)
-            return put_own_property_by_index(property_index, value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
-    }
     return put_own_property(property_name.to_string_or_symbol(), value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
 }
 
@@ -775,12 +755,6 @@ bool Object::delete_property(const PropertyName& property_name)
     if (property_name.is_number())
         return m_indexed_properties.remove(property_name.as_number());
 
-    if (property_name.is_string() && property_name.string_may_be_number()) {
-        i32 property_index = property_name.as_string().to_int().value_or(-1);
-        if (property_index >= 0)
-            return m_indexed_properties.remove(property_index);
-    }
-
     auto metadata = shape().lookup(property_name.to_string_or_symbol());
     if (!metadata.has_value())
         return true;
@@ -836,13 +810,6 @@ Value Object::get(const PropertyName& property_name, Value receiver, bool withou
     if (property_name.is_number())
         return get_by_index(property_name.as_number(), without_side_effects);
 
-    if (property_name.is_string() && property_name.string_may_be_number()) {
-        auto& property_string = property_name.as_string();
-        i32 property_index = property_string.to_int().value_or(-1);
-        if (property_index >= 0)
-            return get_by_index(property_index, without_side_effects);
-    }
-
     if (receiver.is_empty())
         receiver = Value(this);
 
@@ -904,13 +871,6 @@ bool Object::put(const PropertyName& property_name, Value value, Value receiver)
 
     VERIFY(!value.is_empty());
 
-    if (property_name.is_string() && property_name.string_may_be_number()) {
-        auto& property_string = property_name.as_string();
-        i32 property_index = property_string.to_int().value_or(-1);
-        if (property_index >= 0)
-            return put_by_index(property_index, value);
-    }
-
     auto string_or_symbol = property_name.to_string_or_symbol();
 
     if (receiver.is_empty())
@@ -1045,12 +1005,6 @@ bool Object::has_own_property(const PropertyName& property_name) const
     if (property_name.is_number())
         return has_indexed_property(property_name.as_number());
 
-    if (property_name.is_string() && property_name.string_may_be_number()) {
-        i32 property_index = property_name.as_string().to_int().value_or(-1);
-        if (property_index >= 0)
-            return has_indexed_property(property_index);
-    }
-
     return shape().lookup(property_name.to_string_or_symbol()).has_value();
 }
 

Userland/Libraries/LibJS/Runtime/PropertyName.h

@@ -88,10 +88,38 @@ public:
     }
 
     bool is_valid() const { return m_type != Type::Invalid; }
-    bool is_number() const { return m_type == Type::Number; }
+    bool is_number() const
-    bool is_string() const { return m_type == Type::String; }
+    {
+        if (m_type == Type::Number)
+            return true;
+        if (m_type != Type::String || !m_string_may_be_number)
+            return false;
+
+        return const_cast<PropertyName*>(this)->try_coerce_into_number();
+    }
+    bool is_string() const
+    {
+        if (m_type != Type::String)
+            return false;
+        if (!m_string_may_be_number)
+            return true;
+
+        return !const_cast<PropertyName*>(this)->try_coerce_into_number();
+    }
     bool is_symbol() const { return m_type == Type::Symbol; }
-    bool string_may_be_number() const { return m_string_may_be_number; }
+
+    bool try_coerce_into_number()
+    {
+        VERIFY(m_string_may_be_number);
+        i32 property_index = m_string.to_int().value_or(-1);
+        if (property_index < 0) {
+            m_string_may_be_number = false;
+            return false;
+        }
+        m_type = Type::Number;
+        m_number = property_index;
+        return true;
+    }
 
     u32 as_number() const
     {