Raito Bezarius
19ad871b74
Progress towards REUSE compliance. Change-Id: Ia64efc4fbf4e8eb3800b75159f357ea009438ae1 Signed-off-by: Raito Bezarius <raito@lix.systems>
71 lines
2.3 KiB
C++
71 lines
2.3 KiB
C++
// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
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//
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// SPDX-License-Identifier: LGPL-2.1-only
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#pragma once
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///@file
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#include <tao/pegtl.hpp>
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namespace nix::parser {
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// modified copy of change_state, as the manual suggest for more involved
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// state manipulation. we want to change only the first state parameter,
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// and we care about the *initial* position of a rule application (not the
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// past-the-end position as pegtl change_state provides)
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template<typename NewState>
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struct change_head : tao::pegtl::maybe_nothing
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{
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template<
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typename Rule,
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tao::pegtl::apply_mode A,
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tao::pegtl::rewind_mode M,
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template<typename...> class Action,
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template<typename...> class Control,
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typename ParseInput,
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typename State,
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typename... States
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>
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[[nodiscard]] static bool match(ParseInput & in, State && st, States &&... sts)
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{
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const auto begin = in.iterator();
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if constexpr (std::is_constructible_v<NewState, State, States...>) {
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NewState s(st, sts...);
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if (tao::pegtl::match<Rule, A, M, Action, Control>(in, s, sts...)) {
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if constexpr (A == tao::pegtl::apply_mode::action) {
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_success<Action<Rule>>(0, begin, in, s, st, sts...);
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}
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return true;
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}
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return false;
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} else if constexpr (std::is_default_constructible_v<NewState>) {
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NewState s;
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if (tao::pegtl::match<Rule, A, M, Action, Control>(in, s, sts...)) {
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if constexpr (A == tao::pegtl::apply_mode::action) {
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_success<Action<Rule>>(0, begin, in, s, st, sts...);
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}
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return true;
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}
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return false;
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} else {
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static_assert(decltype(sizeof(NewState))(), "unable to instantiate new state");
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}
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}
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template<typename Target, typename ParseInput, typename... S>
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static void _success(void *, auto & begin, ParseInput & in, S & ... sts)
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{
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const typename ParseInput::action_t at(begin, in);
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Target::success(at, sts...);
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}
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template<typename Target, typename... S>
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static void _success(decltype(Target::success0(std::declval<S &>()...), 0), auto &, auto &, S & ... sts)
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{
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Target::success0(sts...);
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}
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};
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}
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