Re: inhibit-read-only text property does not work expectedly

[Eli Zaretskii]

> From: Serhii Mozghovyi <address@hidden>
> Date: Sat, 14 Sep 2019 09:35:41 +0300
> 
> C-x b <unique buffer name>, then insert some text, such as:
> 
> First paragraph.
> 
> Second paragraph.
> 
> Then M-: (put-text-property (point-min) (point-max) 'inhibit-read-only 
> t), and C-x C-q to make the buffer read-only. Now select the "Se" and 
> kill it with C-w: it succeeds. Then hit C-/ to undo, select "Sec" and 
> try to kill again. Now it fails. For any other region that does not 
> intersect with "Se", killing works.

Please file a bug report with all the details.

> I found out that the reason for that is this code in the function 
> "verify_interval_modifications" in textprop.c (lines 2259-2263):
> 
>         if (i->position + LENGTH (i) < end
>             && (!NILP (BVAR (current_buffer, read_only))
>                 && NILP (Vinhibit_read_only)))
>           xsignal1 (Qbuffer_read_only, Fcurrent_buffer ());
> 
> I don't quite understand what is its purpose, anyway? To disable 
> deletion of entire intervals? Does it make any bit of a sense? Intervals 
> should be invisible at Lisp programming level, right?

AFAIU, this code catches the cases where only part of the region to be
deleted has the inhibit-read-only property.

I think the bug is that undo doesn't cause the adjacent intervals to
be spliced or something.