Long case insensitive style also makes short case insensitive.

Start by reproducing the issue with the provided command_line_parser example, especially ./test -A, and trace how long_case_insensitive is handled in the command-line style parsing path. Done means long_case_insensitive no longer makes short options case-insensitive, with the 1.67.0 expected output preserved and a regression test covering the behavior.

When you use the ::long_case_insensitive style it inadvertently behaves as if you also selected ::short_case_insensitive.

I noticed this behavior since boost 1.68.0, compiling with 1.67.0 gives the correct result.

In v1.67.0, if you call the test program below like this, ./test -A, it will give the correct result:

Adam is selected:  false
Alice is selected: true

In v1.68.0 and v1.69.0 it will give the wrong result, as if ::short_case_insensitive was also selected.:

Adam is selected:  true
Alice is selected: false

Basically the -A argument becomes an -a argument.

Example code to illustrate the problem.

#include <iostream>
#include <boost/program_options.hpp>

namespace po = boost::program_options;
namespace po_style = boost::program_options::command_line_style;

int main(int argc, char* argv[]){

        bool adamSelected = false;
        bool aliceSelected = false;


        try{
                po::options_description desc("Allowed options");
                desc.add_options()
                    ("adam,a", po::value<bool>(&adamSelected)->default_value(false)->implicit_value(true),"Choose Adam")
                    ("alice,A", po::value<bool>(&aliceSelected)->default_value(false)->implicit_value(true),"Choose Alice")
                ;

                po::variables_map vm;

                auto parsed = po::command_line_parser(argc, argv).options(desc).style(po_style::unix_style | po_style::long_case_insensitive).run();
                po::store(parsed, vm);

                po::notify(vm);

                std::cout << "Adam is selected:  " << (adamSelected?"true":"false") << std::endl
                        << "Alice is selected: " << (aliceSelected?"true":"false") << std::endl;
        }
        catch(std::exception& e){
                std::cerr << e.what() << std::endl;
        }
        return 0;
}