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Semantic action attached to a parser that has attribute type of unused_type shall not inhibit the outer rule's attribute composition #104
Description
This kind of grammar definition does not alter the semantics of the internal attribute as it's unused_type in the first place. Therefore, there's no reason that we must inhibit the rule parser's attribute handling even when semantic action is attached.
constexpr auto some_rule_grammar_def =
lit("prefix").on_match([](auto&& ctx) {
if (x4::get<some_local_variable>(ctx) == 42) {
do_something();
return true;
}
return false;
}) >>
body_parser
;Fundamentally, the code above shall match the semantics below:
constexpr auto some_rule_grammar_def =
eps([](auto&& ctx) {
if (x4::get<some_local_variable>(ctx) == 42) {
do_something();
return true;
}
return false;
}) >>
body_parser
;Workaround
We can currently use x4::as<x4::unused_type>(...) to explicitly re-enable the inhibited attribute. However it's actually a hack (which I introduced for some good reason) when I implemented x4::as, so it's solely a workaround and should not be the desired way of expressing it in application code.
constexpr auto some_rule_grammar_def =
as<unused_type>(lit("prefix").on_match([](auto&& ctx) { // <----- as<unused_type>(...) added
if (x4::get<some_local_variable>(ctx) == 42) {
do_something();
return true;
}
return false;
})) >>
body_parser
;Additional info
Related: #100
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