bug#22761: Surprising interaction between font-lock, invisible text, and point (self-insert-command and insert behave differently)

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 22761@debbugs.gnu.org
> From: Clément Pit--Claudel <clement.pitclaudel@live.com>
> Date: Mon, 22 Feb 2016 11:03:03 -0500
> 
> On 02/22/2016 10:53 AM, Eli Zaretskii wrote:
> >> From: Clément Pit--Claudel <clement.pitclaudel@live.com> Date: Sun,
> >> 21 Feb 2016 19:19:17 -0500
> >> 
> >> The problem happens when editing ‘a_foo_b’ to replace ‘foo’ by
> >> ‘bar’ (to get ‘a_bar_b’). Removing ‘foo’ leaves ‘__’ in the buffer,
> >> which font-lock recognizes: the whole string gets displayed as
> >> ‘ab’. Even then, the point is still between the two underscores (it
> >> hasn't moved after font-lock added the invisible property to the
> >> underscores). Pressing ‘b’ to start inserting ‘bar’ works fine (I
> >> end up with ‘a_b_c’), except for one thing: the point gets moved
> >> after the second underscore. Thus, pressing ‘ar’ to complete ‘bar’
> >> ends up inserting ‘a_b_arb’.
> > 
> > Did you try binding global-disable-point-adjustment to a non-nil 
> > value?
> 
> I imagine that it would work, but wouldn't it break other parts of Emacs? The mode to which I'm adding this subscripts feature also uses hideshow, for example, and I do want the point to be moved out of invisible sections then.

If it works, perhaps you could bind disable-point-adjustment (not the
global variable) in the insertion commands.

In general, insertion in the middle of invisible text is tricky at
best.  So perhaps you should rethink how you handle this situation --
you could, for example, temporarily remove the entire invisible
portion, until the insertion is complete.