bug#32142: WG: 26.1; Problems with flyspell-region

[R. Diez]

I mentioned some problems with flyspell-region on the help-gnu-emacs mailing 
list here:

https://lists.gnu.org/archive/html/help-gnu-emacs/2018-07/msg00100.html
Issues are:


Issue 1) The spell check is performed just once, and is not updated as I type 
inside that region. This is what I wrote on the mailing list:


"If I mark a region (click on the beginning, hold shift, move to the end), and 
then run flyspell-region, the region gets spell-checked, and all the dictionary 
misses are underlined in red, as expected. But then, if I fix the words, the 
spelling marking (the red underlining) is not removed. It looks like Flyspell 
is not 'live' anymore within that region. The "overlay" is left behind as 
static font faces."
I do not want to activate Flyspell for the whole buffer, because that would 
lead to too much red underlining.

If I just wanted a single-shot, I would use ispell-region instead.

If this cannot be fixed, the current behaviour should be documented.



Issue 2) There is no easy way to remove the red underlining (overlays) left 
behind by flyspell-region. This is what I wrote on the mailing list:

"Often I get too many dictionary misses (too much red underlining). Or I just 
do not want to be distracted anymore. That is the reason why I want to be able 
to turn spell-checking on and off on demand on a particular region. And, when I 
want it off, I want to remove the "overlays" from that region. Why should they 
remain? At the moment, there is no direct way to do that."

I also wrote:

"After some searching, I found out about flyspell-delete-all-overlays and 
flyspell-delete-region-overlays, but alas, they are not marked as 
'interactive'. I wonder how Flyspell thinks users should remove those marks 
(how to end the flyspell-region command)."

Issue 3) Disabling flyspell-persistent-highlight renders flyspell-region 
useless.

Contrary to some of the answers in the mailing list, that combination does not 
work at all. This is what I am seeing:

"What I mean is that, if you turn flyspell-persistent-highlight off, then 
flyspell-region does nothing other than consume CPU cycles. The red underlining 
for dictionary misses does not show up at all."

Again, I do not want to turn on Flyspell for the whole buffer. If 
flyspell-region is supposed to work only when the Flyspell Mode is active, it 
should check, and error if it is not active. But that kind of defeats the 
purpose of having a flyspell-region.