LibJS: Stop using a native property for RegExp's lastIndex property

This is not a functional change, the exposed (incorrect) behaviour is
the same as it was before, this simply removes the last user of
NativeProperties, allowing us to remove them completely from LibJS.

Userland/Libraries/LibJS/AST.cpp

@@ -1993,7 +1993,7 @@ void RegExpLiteral::dump(int indent) const
 Value RegExpLiteral::execute(Interpreter& interpreter, GlobalObject& global_object) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
-    return RegExpObject::create(global_object, pattern(), flags());
+    return regexp_create(global_object, js_string(interpreter.heap(), pattern()), js_string(interpreter.heap(), flags()));
 }
 
 void ArrayExpression::dump(int indent) const

Userland/Libraries/LibJS/Runtime/RegExpConstructor.cpp

@@ -43,20 +43,8 @@ Value RegExpConstructor::call()
 Value RegExpConstructor::construct(FunctionObject&)
 {
     auto& vm = this->vm();
-    String pattern = "";
-    String flags = "";
-    if (!vm.argument(0).is_undefined()) {
-        pattern = vm.argument(0).to_string(global_object());
-        if (vm.exception())
-            return {};
-    }
-    if (!vm.argument(1).is_undefined()) {
-        flags = vm.argument(1).to_string(global_object());
-        if (vm.exception())
-            return {};
-    }
-    // FIXME: Use RegExpAlloc (which uses OrdinaryCreateFromConstructor)
-    return RegExpObject::create(global_object(), pattern, flags);
+    // FIXME: This is non-conforming
+    return regexp_create(global_object(), vm.argument(0), vm.argument(1));
 }
 
 // 22.2.4.2 get RegExp [ @@species ], https://tc39.es/ecma262/#sec-get-regexp-@@species

Userland/Libraries/LibJS/Runtime/RegExpObject.cpp

@@ -100,75 +100,42 @@ RegExpObject::RegExpObject(String pattern, String flags, Object& prototype)
     }
 }
 
-void RegExpObject::initialize(GlobalObject& global_object)
-{
-    auto& vm = this->vm();
-    Object::initialize(global_object);
-
-    define_native_property(vm.names.lastIndex, last_index, set_last_index, Attribute::Writable);
-}
-
 RegExpObject::~RegExpObject()
 {
 }
 
-static RegExpObject* regexp_object_from(VM& vm, GlobalObject& global_object)
-{
-    auto* this_object = vm.this_value(global_object).to_object(global_object);
-    if (!this_object)
-        return nullptr;
-    if (!is<RegExpObject>(this_object)) {
-        vm.throw_exception<TypeError>(global_object, ErrorType::NotA, "RegExp");
-        return nullptr;
-    }
-    return static_cast<RegExpObject*>(this_object);
-}
-
-JS_DEFINE_NATIVE_GETTER(RegExpObject::last_index)
-{
-    auto regexp_object = regexp_object_from(vm, global_object);
-    if (!regexp_object)
-        return {};
-
-    return Value((unsigned)regexp_object->regex().start_offset);
-}
-
-JS_DEFINE_NATIVE_SETTER(RegExpObject::set_last_index)
+void RegExpObject::initialize(GlobalObject& global_object)
 {
-    auto regexp_object = regexp_object_from(vm, global_object);
-    if (!regexp_object)
-        return;
-
-    auto index = value.to_i32(global_object);
-    if (vm.exception())
-        return;
-
-    if (index < 0)
-        index = 0;
-
-    regexp_object->regex().start_offset = index;
+    auto& vm = this->vm();
+    Object::initialize(global_object);
+    define_direct_property(vm.names.lastIndex, {}, Attribute::Writable);
 }
 
 // 22.2.3.2.4 RegExpCreate ( P, F ), https://tc39.es/ecma262/#sec-regexpcreate
 RegExpObject* regexp_create(GlobalObject& global_object, Value pattern, Value flags)
 {
+    auto& vm = global_object.vm();
     String p;
     if (pattern.is_undefined()) {
         p = String::empty();
     } else {
         p = pattern.to_string(global_object);
-        if (p.is_null())
-            return nullptr;
+        if (vm.exception())
+            return {};
     }
     String f;
     if (flags.is_undefined()) {
         f = String::empty();
     } else {
         f = flags.to_string(global_object);
-        if (f.is_null())
-            return nullptr;
+        if (vm.exception())
+            return {};
     }
-    return RegExpObject::create(global_object, move(p), move(f));
+    auto* object = RegExpObject::create(global_object, move(p), move(f));
+    object->set(vm.names.lastIndex, Value(0), true);
+    if (vm.exception())
+        return {};
+    return object;
 }
 
 }

Userland/Libraries/LibJS/Runtime/RegExpObject.h

@@ -36,9 +36,6 @@ public:
     const Regex<ECMA262>& regex() const { return m_regex; }
 
 private:
-    JS_DECLARE_NATIVE_GETTER(last_index);
-    JS_DECLARE_NATIVE_SETTER(set_last_index);
-
     String m_pattern;
     String m_flags;
     Flags m_active_flags;

Userland/Libraries/LibJS/Runtime/RegExpPrototype.cpp

@@ -165,10 +165,25 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::exec)
     StringView str_to_match = str;
 
     // RegExps without "global" and "sticky" always start at offset 0.
-    if (!regexp_object->regex().options().has_flag_set((ECMAScriptFlags)regex::AllFlags::Internal_Stateful))
-        regexp_object->regex().start_offset = 0;
+    if (!regexp_object->regex().options().has_flag_set((ECMAScriptFlags)regex::AllFlags::Internal_Stateful)) {
+        regexp_object->set(vm.names.lastIndex, Value(0), true);
+        if (vm.exception())
+            return {};
+    }
+
+    auto last_index = regexp_object->get(vm.names.lastIndex);
+    if (vm.exception())
+        return {};
+    regexp_object->regex().start_offset = last_index.to_length(global_object);
+    if (vm.exception())
+        return {};
 
     auto result = do_match(regexp_object->regex(), str_to_match);
+
+    regexp_object->set(vm.names.lastIndex, Value(regexp_object->regex().start_offset), true);
+    if (vm.exception())
+        return {};
+
     if (!result.success)
         return js_null();
 
@@ -217,10 +232,25 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::test)
         return {};
 
     // RegExps without "global" and "sticky" always start at offset 0.
-    if (!regexp_object->regex().options().has_flag_set((ECMAScriptFlags)regex::AllFlags::Internal_Stateful))
-        regexp_object->regex().start_offset = 0;
+    if (!regexp_object->regex().options().has_flag_set((ECMAScriptFlags)regex::AllFlags::Internal_Stateful)) {
+        regexp_object->set(vm.names.lastIndex, Value(0), true);
+        if (vm.exception())
+            return {};
+    }
+
+    auto last_index = regexp_object->get(vm.names.lastIndex);
+    if (vm.exception())
+        return {};
+    regexp_object->regex().start_offset = last_index.to_length(global_object);
+    if (vm.exception())
+        return {};
 
     auto result = do_match(regexp_object->regex(), str);
+
+    regexp_object->set(vm.names.lastIndex, Value(regexp_object->regex().start_offset), true);
+    if (vm.exception())
+        return {};
+
     return Value(result.success);
 }
 
@@ -301,8 +331,11 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::symbol_replace)
         return {};
 
     bool global = global_value.to_boolean();
-    if (global)
-        rx->regex().start_offset = 0;
+    if (global) {
+        rx->set(vm.names.lastIndex, Value(0), true);
+        if (vm.exception())
+            return {};
+    }
 
     // FIXME: Implement and use RegExpExec - https://tc39.es/ecma262/#sec-regexpexec
     auto* exec = Value(rx).get_method(global_object, vm.names.exec);
@@ -336,7 +369,15 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::symbol_replace)
         if (match_str.is_empty()) {
             // FIXME: Implement AdvanceStringIndex to take Unicode code points into account - https://tc39.es/ecma262/#sec-advancestringindex
             //        Once implemented, step (8a) of the @@replace algorithm must also be implemented.
-            rx->regex().start_offset += 1;
+            auto last_index = rx->get(vm.names.lastIndex);
+            if (vm.exception())
+                return {};
+            auto this_index = last_index.to_length(global_object);
+            if (vm.exception())
+                return {};
+            rx->set(vm.names.lastIndex, Value(this_index + 1), true);
+            if (vm.exception())
+                return {};
         }
     }