GDB pretty print support

[y9luiz]

It's pretty hard to debug programs with a complex JSON structure such as Json::Value, thinking on that.
I did create a very simple pretty print gdb script that would help you debug and see the content under yours JSON objects.

import gdb
import json
class JsonValuePrinter:
    def __init__(self, val):
        self.val = val

    def _invoke_to_styledString_(self):
        eval_string = f"(({self.val.type.name}*){self.val.address})->toStyledString().c_str()"
        output = json.loads(gdb.parse_and_eval(eval_string).string())
        return str(output)

    def to_string(self):
        return self._invoke_to_styledString_()

def build_pretty_printer(val):
    if str(val.type) == 'Json::Value':
        return JsonValuePrinter(val)

gdb.pretty_printers.append(build_pretty_printer)

The script is pretty simple and just converts the JSON to a styled string representation with the method Json::Value::toStyledString

Would be good to access each member individually, but it's considered more complex task So if someone already have a better script or even would like to improve mine, I would really appreciate it.

Anyways, to use this script just launch gdb in your program, for example:

#include <jsoncpp/json/json.h>
#include <jsoncpp/json/value.h>

#include <iostream>

int main()
{
  Json::Value val;

  val["xd"] = 10;

  Json::Value arr;

  arr.append(val);
  arr.append(val);

  val["complex json"] = arr;

  return 0;
}

compile it

g++ main.cpp -g -O0 -o run
gdb run
source prettyPrint.py

if you try to print val for example, you would see the following output: