better assert() with optional format and varadic args

vigil.h

#pragma once /* Copyright (c) Dmitry "Leo" Kuznetsov 2021 see LICENSE for details */
#include <assert.h> // to prevent further redefinition of assert

// better assert(0 <= i && i < n, "index i=%d out of [0..%d( range", i, n);
// also available as 'swear' and 'implore' instead of assert()
// see: https://github.com/munificent/vigil

#undef assert

#if defined(_DEBUG) || defined(DEBUG) || defined(ASSERT_IN_NDEBUG)
#define assert(b, ...) do { \
    if (!(b)) { assertion_failed(__FILE__, __LINE__, __FUNCTION__, #b, "" __VA_ARGS__); } \
} while (0)
#define swear(condition, ...) assert(condition, ##__VA_ARGS__);
#define implore(condition, ...) assert(condition, ##__VA_ARGS__);
#else
#define assert(condition, ...) do { } while (0)
#define swear(condition, ...) do { } while (0)
#define implore(condition, ...) do { } while (0)
#endif

void assertion_failed(const char* file, int line, const char* function,
                      const char* condition, const char* format, ...) __printflike(5, 6);

// implement your own assertion_failed, or define:

#ifdef VIGIL_IMPLEMENTATION

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static const char* assertion_failed_filename(const char* file) {
    char* fn = strrchr(file, '/');
    if (fn == (void*)0) { fn = strrchr(file, '\\'); }
    return fn != (void*)0 ? fn + 1 : file;
}

void assertion_failed(const char* file, int line, const char* function,
                      const char* condition, const char* format, ...) {
    const char* fn = assertion_failed_filename(file);
    const int n = (int)strlen(format);
    if (n == 0) {
        fprintf(stderr, "%s:%d %s() assertion failed: \"%s\"", fn, line, function, condition);
    } else {
        fprintf(stderr, "%s:%d %s() assertion failed: \"%s\" ",  fn, line, function, condition);
        va_list va;
        va_start(va, format);
        vfprintf(stderr, format, va);
        va_end(va);
    }
    if (n == 0 || format[n - 1] != '\n') { fprintf(stderr, "\n"); }
    abort();
}

#endif // VIGIL_IMPLEMENTATION