bug#30823: 25.3; modification-hooks of overlays are not run in some cases

[Noam Postavsky <npostavs@gmail.com>]

Noam Postavsky <npostavs@gmail.com> writes:

> @@ -10403,6 +10403,13 @@ message_dolog (const char *m, ptrdiff_t nbytes, bool nlflag, bool multibyte)
>  	  ptrdiff_t this_bol, this_bol_byte, prev_bol, prev_bol_byte;
>  	  printmax_t dups;
>  
> +          /* Since we call del_range_both passing false for PREPARE,
> +             we aren't prepared to run modification hooks (we could
> +             end up calling modification hooks from another buffer and
> +             only with AFTER=t, Bug#21824).  */
> +          ptrdiff_t count = SPECPDL_INDEX ();
> +          specbind (Qinhibit_modification_hooks, Qt);
> +
>  	  insert_1_both ("\n", 1, 1, true, false, false);
>  
>  	  scan_newline (Z, Z_BYTE, BEG, BEG_BYTE, -2, false);

Coming back to this, there is also the possibility of passing true for
PREPARE, though I'm not sure if that would be better or worse.  Any
comments?

(adding Stefan to Cc since I think this somewhat relates to/collides
with the patch for *Messages* buffer text properties in
https://lists.gnu.org/archive/html/emacs-devel/2018-05/msg00600.html).