bug#30204: 27.0.50; Changing major mode resets non-default invisibility spec

[Lars Ingebrigtsen]

Philipp <p.stephani2@gmail.com> writes:

>> And I think this is correct behaviour -- if you've switched to
>> fundamental-mode, then you don't want these remnants from markdown-mode
>> to survive, I think?
>
> Yes, but they do survive, i.e. once markdown-mode has made some text
> conditionally-visible (which it does for URLs etc.), I'd expect it to
> become unconditionally-visible instead of unconditionally-invisible
> when changing the major mode.

That's true.  Hm...  Should major modes remove `invisible' text
properties (where the value isn't t)?  No, that wouldn't be right,
either.

Uhm.  OK, if `buffer-invisibility-spec' isn't t,
`kill-all-local-variables' could remove the `invisible' text property
from all text that has a non-t value?

That sounds like it would potentially be expensive, but a non-nil
invisibility spec is quite unusual (and switching major modes, in
general, is unusual (well, switching from anything but fundamental-mode
is unusual)).

I dunno.  Anybody have an opinion here?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no