GNU bug report logs - #19188
point adjustemnt moves *into* invisible text

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From: Jonas Bernoulli <jonas <at> bernoul.li>
To: 19188 <at> debbugs.gnu.org
Subject: bug#19188: point adjustemnt moves *into* invisible text
Date: Wed, 26 Nov 2014 04:07:04 +0100

When moving backward "point adjustment" which is supposed to move
point out of an invisible region may end up doing the opposite.

This problem exists at least in 24.3 and 24.4.

1. Yank this in an empty buffer in fundamental-mode and evaluate it.

(progn
  (goto-char (point-min))
  (insert "1\n"
	  (propertize "3\n" 'invisible t)
	  "5\n"
	  "7\n")
	  (backward-char 2))

2. The cursor is now on the "7", which also is the 7th character.

   The buffer looks like
   .-----
   |1
   |5
   |7
   |(progn
   |...
   `-----

   The cursor sits on the "7" and

     M-: (point) => 7
   
3. Move to "5" using e.g. C-p or C-b C-b.

   The cursor is now on "5", which also is the 5th character.

   However point is not were the cursor is

     M-: (point) => 3

The problem is in the code that is supposed to move point *out* of an
invisible region, does the opposite when moving backward places point
on the first character after an invisible region.  It moves to the
beginning of the preceding invisible region.

When point adjustment is disabled (non-nil disable-point-adjustment or
global-disable-point-adjustment) then this does not happen.

It also does not happen when moving forward, e.g. starting at "1"
C-p C-f places the cursor on "5" *and* point is also 5.

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