On Wed, 19 Feb 2020, 04:27 Eli Zaretskii, <eliz@gnu.org> wrote:

I thought in the scenario we are discussing there will be no bitmaps
shown at all, since the scenario disables the fringes. Isn't that so?

If the user turns fringe-mode back on, diff-hl will use the previously created bitmaps, which will be width 1 if define-fringe-bitmap decides to use that instead of zero, or will crash if x_cr_define_fringe_bitmap does not define the bitmap when width == 0

Maybe signaling an error is best :-)