usage.c: add BUG() function

There's a convention in Git's code base to write assertions

  if (...some_bad_thing...)
	die("BUG: the terrible thing happened");

with the idea that users should never see a "BUG:" message
(but if they, it at least gives a clue what happened).  We
use die() here because it's convenient, but there are a few

  1. Without parsing the messages, it's hard for callers to
     distinguish BUG assertions from regular errors.

     For instance, it would be nice if the test suite could
     check that we don't hit any assertions, but
     test_must_fail will pass BUG deaths as OK.

  2. It would be useful to add more debugging features to
     BUG assertions, like file/line numbers or dumping core.

  3. The die() handler can be replaced, and might not
     actually exit the whole program (e.g., it may just
     pthread_exit()). This is convenient for normal errors,
     but for an assertion failure (which is supposed to
     never happen), we're probably better off taking down
     the whole process as quickly and cleanly as possible.

We could address these by checking in die() whether the
error message starts with "BUG", and behaving appropriately.
But there's little advantage at that point to sharing the
die() code, and only downsides (e.g., we can't change the
BUG() interface independently). Moreover, converting all of
the existing BUG calls reveals that the test suite does
indeed trigger a few of them.

Instead, this patch introduces a new BUG() function, which
prints an error before dying via SIGABRT. This gives us test
suite checking and core dumps.  The function is actually a
macro (when supported) so that we can show the file/line

We can convert die("BUG") invocations to BUG() in further
patches, dealing with any test fallouts individually.

Signed-off-by: Jeff King <>
Signed-off-by: Junio C Hamano <>
Jeff King 5 years ago committed by Junio C Hamano
parent b06d364310
commit d8193743e0
  1. 9
  2. 32

@ -1064,6 +1064,15 @@ static inline int regexec_buf(const regex_t *preg, const char *buf, size_t size,
__attribute__((format (printf, 3, 4))) NORETURN
void BUG_fl(const char *file, int line, const char *fmt, ...);
#define BUG(...) BUG_fl(__FILE__, __LINE__, __VA_ARGS__)
__attribute__((format (printf, 1, 2))) NORETURN
void BUG(const char *fmt, ...);
* Preserves errno, prints a message, but gives no warning for ENOENT.
* Returns 0 on success, which includes trying to unlink an object that does

@ -201,3 +201,35 @@ void warning(const char *warn, ...)
warn_routine(warn, params);
static NORETURN void BUG_vfl(const char *file, int line, const char *fmt, va_list params)
char prefix[256];
/* truncation via snprintf is OK here */
if (file)
snprintf(prefix, sizeof(prefix), "BUG: %s:%d: ", file, line);
snprintf(prefix, sizeof(prefix), "BUG: ");
vreportf(prefix, fmt, params);
void BUG_fl(const char *file, int line, const char *fmt, ...)
va_list ap;
va_start(ap, fmt);
BUG_vfl(file, line, fmt, ap);
void BUG(const char *fmt, ...)
va_list ap;
va_start(ap, fmt);
BUG_vfl(NULL, 0, fmt, ap);