bug#19442: 25.0.50; Overflowing newline into right fringe requires left fringe to be nonempty

bug#19442: 25.0.50; Overflowing newline into right fringe requires left fringe to be nonempty

[Kirill Ignatiev]

According to overflow-newline-into-fringe's docstring, when point is
that the end of a line that is as wide as the frame the point should
be displayed in the right fringe.

However, it seems that on 25.0.50 (with -Q), it requires both the
right *and* the left fringe to be non-empty. If the left fringe is
empty, the newline does not overflow into the right fringe, as the
documentation and common sense says it should.

(setq overflow-newline-into-fringe t)
(dolist (x '((cursor-type . box)
             (cursor-color . "red")
             (width . 80)
             (left-fringe . 8) ; change this to 0
             (right-fringe . 8)))
  (set-frame-parameter (selected-frame) (car x) (cdr x)))
;; (progn (insert "\n;") (dotimes (x 79) (insert ?x)))
;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

In GNU Emacs 25.0.50.36 (x86_64-apple-darwin13.4.0, NS appkit-1265.21
Version 10.9.5 (Build 13F34))

bug#19442: 25.0.50; Overflowing newline into right fringe requires left fringe to be nonempty

[Eli Zaretskii]

> Date: Thu, 25 Dec 2014 19:16:13 -0500
> From: Kirill Ignatiev <kirill.ignatiev@gmail.com>
> 
> According to overflow-newline-into-fringe's docstring, when point is
> that the end of a line that is as wide as the frame the point should
> be displayed in the right fringe.
> 
> However, it seems that on 25.0.50 (with -Q), it requires both the
> right *and* the left fringe to be non-empty. If the left fringe is
> empty, the newline does not overflow into the right fringe, as the
> documentation and common sense says it should.
> 
> (setq overflow-newline-into-fringe t)
> (dolist (x '((cursor-type . box)
>              (cursor-color . "red")
>              (width . 80)
>              (left-fringe . 8) ; change this to 0
>              (right-fringe . 8)))
>   (set-frame-parameter (selected-frame) (car x) (cdr x)))
> ;; (progn (insert "\n;") (dotimes (x 79) (insert ?x)))
> ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

This is not a bug.

You insert too many characters in that line.  Insert only 79 of them,
including the semi-colon, and you will see the newline overflow into
the right fringe, as documented.

When one of the fringes is missing, the display engine reserves one
column for the continuation glyph, so you have one column less for
characters.  For more details about this, see

  http://debbugs.gnu.org/cgi/bugreport.cgi?bug=19395#32

and a few follow-ups after that.

If you want to avoid losing 1 full column, set the left fringe to 1
pixel, not zero.