Segfault when trying to dump a grammar state machine

[mingodad]

When there is no rules in the grammar (lexer declarations only) and we try to dump the grammar state machine we get a segfault. This https://github.com/mingodad/parsertl-playground/commit/96890dfd4af6b80f9f64ac118ac6c0194450bcf2 seems to fix it.

[BenHanson]

I tried:

    parsertl::rules rules;
    parsertl::state_machine sm;

    parsertl::generator::build(rules, sm);

Which threw an exception saying "No productions are defined."

[mingodad]

The segfault happens when trying to dump the state machine of a user grammar in playground.cpp that is a variant of gram_grep:

The problem can be seem when adding the code shown bellow here https://github.com/BenHanson/gram_grep/blob/23d06f813ba0c58735a1278c5af0a7aed416f573/main.cpp#L431:

        if(true /*gs.dump_grammar_gsm*/)
        {
            parsertl::dfa dfa_;
            parsertl::generator::build_dfa(gs.user_parser.grules, dfa_);  //!!!! segfaults inside build_dfa
            parsertl::debug::dump(gs.user_parser.grules, dfa_, std::cout);
            return false;
        }

[BenHanson]

Done