LibWeb/IDL: Add support for optional sequences

Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp

@@ -707,6 +707,41 @@ static void generate_to_cpp(SourceGenerator& generator, ParameterType& parameter
         // 3. If method is undefined, throw a TypeError.
         // 4. Return the result of creating a sequence from V and method.
 
+        if (optional) {
+            auto sequence_cpp_type = idl_type_name_to_cpp_type(parameterized_type.parameters.first(), interface);
+            sequence_generator.set("sequence.type", sequence_cpp_type.name);
+            sequence_generator.set("sequence.storage_type", sequence_storage_type_to_cpp_storage_type_name(sequence_cpp_type.sequence_storage_type));
+
+            if (!optional_default_value.has_value()) {
+                if (sequence_cpp_type.sequence_storage_type == IDL::SequenceStorageType::Vector) {
+                    sequence_generator.append(R"~~~(
+    Optional<@sequence.storage_type@<@sequence.type@>> @cpp_name@;
+)~~~");
+                } else {
+                    sequence_generator.append(R"~~~(
+    Optional<@sequence.storage_type@> @cpp_name@;
+)~~~");
+                }
+            } else {
+                if (optional_default_value != "[]")
+                    TODO();
+
+                if (sequence_cpp_type.sequence_storage_type == IDL::SequenceStorageType::Vector) {
+                    sequence_generator.append(R"~~~(
+    @sequence.storage_type@<@sequence.type@> @cpp_name@;
+)~~~");
+                } else {
+                    sequence_generator.append(R"~~~(
+    @sequence.storage_type@ @cpp_name@ { global_object.heap() };
+)~~~");
+                }
+            }
+
+            sequence_generator.append(R"~~~(
+    if (!@js_name@@js_suffix@.is_undefined()) {
+)~~~");
+        }
+
         sequence_generator.append(R"~~~(
     if (!@js_name@@js_suffix@.is_object())
         return vm.throw_completion<JS::TypeError>(global_object, JS::ErrorType::NotAnObject, @js_name@@js_suffix@.to_string_without_side_effects());
@@ -716,7 +751,14 @@ static void generate_to_cpp(SourceGenerator& generator, ParameterType& parameter
         return vm.throw_completion<JS::TypeError>(global_object, JS::ErrorType::NotIterable, @js_name@@js_suffix@.to_string_without_side_effects());
 )~~~");
 
-        parameterized_type.generate_sequence_from_iterable(sequence_generator, acceptable_cpp_name, String::formatted("{}{}", js_name, js_suffix), String::formatted("iterator_method{}", recursion_depth), interface, recursion_depth + 1);
+        parameterized_type.generate_sequence_from_iterable(sequence_generator, String::formatted("{}{}", acceptable_cpp_name, optional ? "_non_optional" : ""), String::formatted("{}{}", js_name, js_suffix), String::formatted("iterator_method{}", recursion_depth), interface, recursion_depth + 1);
+
+        if (optional) {
+            sequence_generator.append(R"~~~(
+        @cpp_name@ = move(@cpp_name@_non_optional);
+    }
+)~~~");
+        }
     } else if (parameter.type->name == "record") {
         // https://webidl.spec.whatwg.org/#es-record