date -d "next thur"

Version:

coreutils-7.2 (fixed in 7.3)

How to reproduce?

If today’s date is Thursday (Sept. 6, 2012), then run the following command:

$ coreutils-7.2/src/date -d "next thur"

Symptom:

Wrong result.

The output printed:

Thu Sep  6 00:00:00 PDT 2012

However, the correct output should be

Thu Sep 13 00:00:00 PDT 2012

Root cause:

The problem is because of getdate.y -- wrong calculation.

In getdate.y, the parser interpret the “next wed” differently.

get_date {

…

/* tm is a struct storing the time info of the current time,

   where tm_wday stores the day of week [0-6]. In this case

   tm.tm_wday = 4.

   pc stores the command-line arg parsing info. So

   pc.day_number stores the day of week of the request (in this case

   pc.day_number equals 4 since the command arg is “next thur”).

   So the bug is that originally it didn’t expect the case where

   tm.tm_wday == pc.day_number (both thursday). */

tm.tm_mday += ((pc.day_number - tm.tm_wday + 7) % 7

        + 7 * (pc.day_ordinal -

+          (0 < pc.day_ordinal

+               && tm.tm_wday == pc.day_number)));

-          (0 < pc.day_ordinal)));

}

Is there an error message?

No.

Can Errlog/developer anticipate an error message?

No. The error condition is subtle, and if we assume developers can anticipate the error, it means they can fix the bug