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#pragma once
///@file
#include <tao/pegtl.hpp>
namespace nix::parser {
// modified copy of change_state, as the manual suggest for more involved
// state manipulation. we want to change only the first state parameter,
// and we care about the *initial* position of a rule application (not the
// past-the-end position as pegtl change_state provides)
template<typename NewState>
struct change_head : tao::pegtl::maybe_nothing
{
template<
typename Rule,
tao::pegtl::apply_mode A,
tao::pegtl::rewind_mode M,
template<typename...> class Action,
template<typename...> class Control,
typename ParseInput,
typename State,
typename... States
>
[[nodiscard]] static bool match(ParseInput & in, State && st, States &&... sts)
{
const auto begin = in.iterator();
if constexpr (std::is_constructible_v<NewState, State, States...>) {
NewState s(st, sts...);
if (tao::pegtl::match<Rule, A, M, Action, Control>(in, s, sts...)) {
if constexpr (A == tao::pegtl::apply_mode::action) {
_success<Action<Rule>>(0, begin, in, s, st, sts...);
}
return true;
}
return false;
} else if constexpr (std::is_default_constructible_v<NewState>) {
NewState s;
if (tao::pegtl::match<Rule, A, M, Action, Control>(in, s, sts...)) {
if constexpr (A == tao::pegtl::apply_mode::action) {
_success<Action<Rule>>(0, begin, in, s, st, sts...);
}
return true;
}
return false;
} else {
static_assert(decltype(sizeof(NewState))(), "unable to instantiate new state");
}
}
template<typename Target, typename ParseInput, typename... S>
static void _success(void *, auto & begin, ParseInput & in, S & ... sts)
{
const typename ParseInput::action_t at(begin, in);
Target::success(at, sts...);
}
template<typename Target, typename... S>
static void _success(decltype(Target::success0(std::declval<S &>()...), 0), auto &, auto &, S & ... sts)
{
Target::success0(sts...);
}
};
}
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