On Thu, Sep 29, 2016 at 8:54 PM, Junio C Hamano <gitster@pobox.com> wrote:
>
>  * The script uses "git rev-parse --short HEAD"; I suspect that it
>    says "ah, default_abbrev is -1 and minimum_abbrev is 4, so let's
>    try abbreviating to 4 hexdigits".

Ahh, right you are. The logic there is

                                abbrev = DEFAULT_ABBREV;
                                if (arg[7] == '=')
                                        abbrev = strtoul(arg + 8, NULL, 10);
                                if (abbrev < MINIMUM_ABBREV)
                                        abbrev = MINIMUM_ABBREV;
                                ....

which now does something different than what it used to do because
DEFAULT_ABBREV is -1.

Putting the "sanity-check the abbrev range" tests inside the "if()"
statement that does strtoul() should fix it. Let me test...

[ short time passes ]

Yup. Incremental patch for that single issue attached.  I made it do
an early "continue" instead of adding another level on indentation.

                 Linus