Boost spirit parsing objective-C like language - c++

Question

I'm trying to use boost's spirit to reimplement the logos parsing perl script from iPhone jailbreaking development.
An example of input is:
%hook SBLockScreenView
-(void)setCustomSlideToUnlockText:(id)arg1
{
arg1 = #"Changed the slider";
%orig(arg1);
}
%end
I so far have:
namespace logos
{
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
struct class_hook
{
std::string class_name;
std::string method_signature;
std::string method_body;
};
template <typename Iterator>
struct class_hook_parser : qi::grammar<Iterator, class_hook(), ascii::space_type>
{
class_hook_parser() : class_hook_parser::base_type(start)
{
using qi::int_;
using qi::lit;
using qi::on_error;
using qi::fail;
using qi::double_;
using qi::lexeme;
using ascii::char_;
hooked_class %= lexeme[+(char_("a-zA-Z") - '-')];
method_sig %= lexeme[+(char_) - '{'];
method_body %= lexeme[+(char_ - '}')];
start %=
lit("%hook")
>> hooked_class
>> method_sig
>> method_body
>> lit("%end")
;
on_error<fail>
(
start,
boost::phoenix::ref(std::cout) << "Something errored!" << std::endl);
}
qi::rule<Iterator, std::string(), ascii::space_type> hooked_class;
qi::rule<Iterator, std::string(), ascii::space_type> method_sig;
qi::rule<Iterator, std::string(), ascii::space_type> method_body;
qi::rule<Iterator, class_hook(), ascii::space_type> start;
};
}
BOOST_FUSION_ADAPT_STRUCT(logos::class_hook,
(std::string, class_name)
(std::string, method_signature)
(std::string, method_body))
typedef std::string::const_iterator iterator_type;
typedef logos::class_hook_parser<iterator_type> class_hook_parser;
using boost::spirit::ascii::space;
std::string::const_iterator
iter = std::begin(tweak_source_code),
end = std::end(tweak_source_code);
class_hook_parser g;
logos::class_hook emp;
bool r = phrase_parse(iter, end, g, space, emp);
if (r) {
std::cout << "Got: " << boost::fusion::as_vector(emp) << std::endl;
}
else std::cout << "Something isn't working" << std::endl;
But this oddly only prints out the Something isn't working message, not the on_fail callback. Where is my mistake in the parsing and how can I get actually working and informative parse error messages?

Answer 1

Did you mean
+(char_ - '{')
instead of
+(char_) - '{'
And likely, you'd require the body to begin with that { that was rejected as part of the signature. Here's my fixed version:
hooked_class = +char_("a-zA-Z");
method_sig = +(char_ - '{');
method_body = '{' >> +(char_ - '}') >> '}';
Notes:
Dropping the skipper allows you to drop the lexeme[] directive too.
Rejecting - from the "a-zA-Z" set is useless (it's not in it...).
method_sig now includes all whitespace (including the trailing newline)
Use BOOST_SPIRIT_DEBUG to get insight in why your grammar works in mysterious ways
See also: Boost spirit skipper issues
Live On Coliru
//#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace logos
{
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
struct class_hook
{
std::string class_name;
std::string method_signature;
std::string method_body;
};
template <typename Iterator>
struct class_hook_parser : qi::grammar<Iterator, class_hook(), ascii::space_type>
{
class_hook_parser() : class_hook_parser::base_type(start)
{
using qi::int_;
using qi::lit;
using qi::on_error;
using qi::fail;
using qi::double_;
using qi::lexeme;
using ascii::char_;
hooked_class = +char_("a-zA-Z");
method_sig = +(char_ - '{');
method_body = '{' >> +(char_ - '}') >> '}';
start = "%hook"
>> hooked_class
>> method_sig
>> method_body
>> "%end"
;
on_error<fail> (start,
boost::phoenix::ref(std::cout) << "Something errored\n"
);
BOOST_SPIRIT_DEBUG_NODES((hooked_class)(method_sig)(method_body)(start))
}
private:
qi::rule<Iterator, std::string()> hooked_class, method_sig, method_body;
qi::rule<Iterator, class_hook(), ascii::space_type> start;
};
}
BOOST_FUSION_ADAPT_STRUCT(logos::class_hook, class_name, method_signature, method_body)
int main() {
typedef std::string::const_iterator iterator_type;
typedef logos::class_hook_parser<iterator_type> class_hook_parser;
std::string const tweak_source_code = R"(
%hook SBLockScreenView
-(void)setCustomSlideToUnlockText:(id)arg1
{
arg1 = #"Changed the slider";
%orig(arg1);
}
%end
)";
using boost::spirit::ascii::space;
iterator_type iter = std::begin(tweak_source_code), end = std::end(tweak_source_code);
class_hook_parser g;
logos::class_hook emp;
bool r = phrase_parse(iter, end, g, space, emp);
if (r) {
std::cout << "Got: " << boost::fusion::as_vector(emp) << "\n";
} else {
std::cout << "Something isn't working\n";
}
}
Prints
Got: (SBLockScreenView -(void)setCustomSlideToUnlockText:(id)arg1
arg1 = #"Changed the slider";
%orig(arg1);
)