nix-super/src/libutil/fmt.hh

#pragma once
///@file

#include <boost/format.hpp>
#include <string>
#include "ansicolor.hh"


namespace nix {


/**
 * Inherit some names from other namespaces for convenience.
 */
using boost::format;


/**
 * A variadic template that does nothing. Useful to call a function
 * for all variadic arguments but ignoring the result.
 */
struct nop { template<typename... T> nop(T...) {} };


/**
 * A helper for formatting strings. ‘fmt(format, a_0, ..., a_n)’ is
 * equivalent to ‘boost::format(format) % a_0 % ... %
 * ... a_n’. However, ‘fmt(s)’ is equivalent to ‘s’ (so no %-expansion
 * takes place).
 */
template<class F>
inline void formatHelper(F & f)
{
}

template<class F, typename T, typename... Args>
inline void formatHelper(F & f, const T & x, const Args & ... args)
{
    formatHelper(f % x, args...);
}

inline std::string fmt(const std::string & s)
{
    return s;
}

inline std::string fmt(std::string_view s)
{
    return std::string(s);
}

inline std::string fmt(const char * s)
{
    return s;
}

template<typename... Args>
inline std::string fmt(const std::string & fs, const Args & ... args)
{
    boost::format f(fs);
    f.exceptions(boost::io::all_error_bits ^ boost::io::too_many_args_bit);
    formatHelper(f, args...);
    return f.str();
}

// format function for hints in errors.  same as fmt, except templated values
// are always in magenta.
template <class T>
struct magentatxt
{
    magentatxt(const T &s) : value(s) {}
    const T & value;
};

template <class T>
std::ostream & operator<<(std::ostream & out, const magentatxt<T> & y)
{
    return out << ANSI_WARNING << y.value << ANSI_NORMAL;
}

template <class T>
struct normaltxt
{
    normaltxt(const T & s) : value(s) {}
    const T & value;
};

template <class T>
std::ostream & operator<<(std::ostream & out, const normaltxt<T> & y)
{
    return out << ANSI_NORMAL << y.value;
}

class hintformat
{
public:
    hintformat(const std::string & format) : fmt(format)
    {
        fmt.exceptions(boost::io::all_error_bits ^
                       boost::io::too_many_args_bit ^
                       boost::io::too_few_args_bit);
    }

    hintformat(const hintformat & hf)
        : fmt(hf.fmt)
    { }

    hintformat(format && fmt)
        : fmt(std::move(fmt))
    { }

    template<class T>
    hintformat & operator%(const T & value)
    {
        fmt % magentatxt(value);
        return *this;
    }

    template<class T>
    hintformat & operator%(const normaltxt<T> & value)
    {
        fmt % value.value;
        return *this;
    }

    std::string str() const
    {
        return fmt.str();
    }

private:
    format fmt;
};

std::ostream & operator<<(std::ostream & os, const hintformat & hf);

template<typename... Args>
inline hintformat hintfmt(const std::string & fs, const Args & ... args)
{
    hintformat f(fs);
    formatHelper(f, args...);
    return f;
}

inline hintformat hintfmt(const std::string & plain_string)
{
    // we won't be receiving any args in this case, so just print the original string
    return hintfmt("%s", normaltxt(plain_string));
}

}