Throw custom error per rule

[MahaZaid]

I have a grammar as follows

struct andOperator : TAO_PEGTL_STRING("AND") {};
struct keyword: minus<identifier, andOperator >{};
struct atomic: seq< keyword, andOperator , keyword >{};
struct expression: must<atomic> {};

And I have a custom error message for every rule as follows:

template <>inline const std::string errors<query:: andOperator >::error_message = "andOperator";
template <>inline const std::string errors<query:: keyword >::error_message = "invalid keyword";
template <>inline const std::string errors<query:: atomic >::error_message = "atomic";
template <>inline const std::string errors<query:: expression >::error_message = "expression";

If my query is for example AND so it will not match the expression but it will fail in the rule atomic, so the error message I get is atomic.

my question: is there any way to track the problem back to keyword rule
so that the error message that will be thrown would be invalid keyword, the one specified in keyword error message ?

[d-frey]

You could unroll minus back to rematch and use the inner rule to raise an error directly:

struct andOperator : TAO_PEGTL_STRING("AND") {};
struct invalidKeyword {};
struct keyword: rematch<identifier, not_at< andOperator, eof, raise< invalidKeyword > > > {};
struct atomic: seq< keyword, plus<space>, andOperator, plus<space>, keyword >{};
struct expression: must<atomic> {};

Now it will use the error message specialization for invalidKeyword when an identifier matches a keyword.

[ColinH]

I'm assuming that your question was answered, if not please feel free to continue here and/or reopen this issue.