Statically error out on a given date.

error_on_date.hpp

namespace error_on_date {
    inline constexpr bool strequal(char const *a, char const *b) {
        return *a == *b && (*a == '\0' || strequal(a + 1, b + 1));
    }
}

#if defined(ERROR_ON_DATE$$USE_CLASS) && ERROR_ON_DATE$$USE_CLASS
    namespace error_on_date {
        struct date {
            constexpr date(unsigned int year, unsigned int month, unsigned int day):
                array{
                    months[month-1][0], months[month-1][1], months[month-1][2],
                    ' ',
                    static_cast<char>(day < 10 ? ' ' : day/10 + '0'),  static_cast<char>(day%10 + '0'),
                    ' ',
                    static_cast<char>(year/1000 + '0'), static_cast<char>(year/100%10 + '0'), static_cast<char>(year/10%10 + '0'), static_cast<char>(year%10 + '0'),
                    '\0'
                }
            {}

            constexpr bool is_today() const noexcept {
                return strequal(__DATE__, array);
            }

        private:
            const char array[12];

            static constexpr const char months[12][3] = {
                { 'J', 'a', 'n' },
                { 'F', 'e', 'b' },
                { 'M', 'a', 'r' },
                { 'A', 'p', 'r' },
                { 'M', 'a', 'y' },
                { 'J', 'u', 'n' },
                { 'J', 'u', 'l' },
                { 'A', 'u', 'g' },
                { 'S', 'e', 'p' },
                { 'O', 'c', 't' },
                { 'N', 'o', 'v' },
                { 'D', 'e', 'c' },
            };
        };
    }

#   define ERROR_ON_DATE(year, month, day, msg) static_assert(!error_on_date::date(year, month, day).is_today(), msg)
#else
#   define ERROR_ON_DATE$$MONTH_1  "Jan"
#   define ERROR_ON_DATE$$MONTH_2  "Feb"
#   define ERROR_ON_DATE$$MONTH_3  "Mar"
#   define ERROR_ON_DATE$$MONTH_4  "Apr"
#   define ERROR_ON_DATE$$MONTH_5  "May"
#   define ERROR_ON_DATE$$MONTH_6  "Jun"
#   define ERROR_ON_DATE$$MONTH_7  "Jul"
#   define ERROR_ON_DATE$$MONTH_8  "Aug"
#   define ERROR_ON_DATE$$MONTH_9  "Sep"
#   define ERROR_ON_DATE$$MONTH_10 "Oct"
#   define ERROR_ON_DATE$$MONTH_11 "Nov"
#   define ERROR_ON_DATE$$MONTH_12 "Dec"

#   define ERROR_ON_DATE$$DAY_1  " 1"
#   define ERROR_ON_DATE$$DAY_2  " 2"
#   define ERROR_ON_DATE$$DAY_3  " 3"
#   define ERROR_ON_DATE$$DAY_4  " 4"
#   define ERROR_ON_DATE$$DAY_5  " 5"
#   define ERROR_ON_DATE$$DAY_6  " 6"
#   define ERROR_ON_DATE$$DAY_7  " 7"
#   define ERROR_ON_DATE$$DAY_8  " 8"
#   define ERROR_ON_DATE$$DAY_9  " 9"
#   define ERROR_ON_DATE$$DAY_10 "10"
#   define ERROR_ON_DATE$$DAY_11 "11"
#   define ERROR_ON_DATE$$DAY_12 "12"
#   define ERROR_ON_DATE$$DAY_13 "13"
#   define ERROR_ON_DATE$$DAY_14 "14"
#   define ERROR_ON_DATE$$DAY_15 "15"
#   define ERROR_ON_DATE$$DAY_16 "16"
#   define ERROR_ON_DATE$$DAY_17 "17"
#   define ERROR_ON_DATE$$DAY_18 "18"
#   define ERROR_ON_DATE$$DAY_19 "19"
#   define ERROR_ON_DATE$$DAY_20 "20"
#   define ERROR_ON_DATE$$DAY_21 "21"
#   define ERROR_ON_DATE$$DAY_22 "22"
#   define ERROR_ON_DATE$$DAY_23 "23"
#   define ERROR_ON_DATE$$DAY_24 "24"
#   define ERROR_ON_DATE$$DAY_25 "25"
#   define ERROR_ON_DATE$$DAY_26 "26"
#   define ERROR_ON_DATE$$DAY_27 "27"
#   define ERROR_ON_DATE$$DAY_28 "28"
#   define ERROR_ON_DATE$$DAY_29 "29"
#   define ERROR_ON_DATE$$DAY_30 "30"
#   define ERROR_ON_DATE$$DAY_31 "31"

#   define ERROR_ON_DATE$$DATE(year, month, day) ERROR_ON_DATE$$MONTH_##month " " ERROR_ON_DATE$$DAY_##day " " #year

#   define ERROR_ON_DATE(year, month, day, msg) static_assert(!error_on_date::strequal(__DATE__, ERROR_ON_DATE$$DATE(year, month, day)), msg)
#endif

error_on_date_example.cpp

#include "error_on_date.hpp"

ERROR_ON_DATE(2019, 6, 26, "Dude, check your code!");