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Re: /* FIXME: Call signal_after_change! */ in callproc.c. Well, why no

From: Eli Zaretskii
Subject: Re: /* FIXME: Call signal_after_change! */ in callproc.c. Well, why not?
Date: Sat, 21 Dec 2019 20:11:01 +0200

> Date: Sat, 21 Dec 2019 17:23:24 +0000
> From: Alan Mackenzie <address@hidden>
>             /* FIXME: Call signal_after_change!  */
> +              beg = PT;

Can you tell why you needed this variable and the assignment?  AFAIK,
PT doesn't change when we call decode_coding_c_string.

>             decode_coding_c_string (&process_coding,
>                                     (unsigned char *) buf, nread, curbuf);
>             unbind_to (count1, Qnil);
> +              signal_after_change (beg, 0, PT - beg);
>             if (display_on_the_fly
>                 && CODING_REQUIRE_DETECTION (&saved_coding)
>                 && ! CODING_REQUIRE_DETECTION (&process_coding))
> , and this appears to solve the OP's problem.
> However, a few lines further on, there's a del_range_2 call inside a condition
> I don't understand (though might, with a great deal of study).  I suspect that
> the call to signal_after_change ought to take this del_range_2 into account,
> possibly coming after it.
> Would somebody who's familiar with this bit of callproc.c please help me out
> here, and explain what this call to del_range_2 is doing, and whether there's
> anything basically wrong with my simple-minded addition of
> signal_after_change.

I'm not sure what you want to hear.  The del_range_2 call deletes the
just-inserted text, because the condition means that text was inserted
using the wrong coding-system to decode the incoming bytes.  What does
that mean for the modification hooks, I don't know: the
before-change-functions were already called, but nothing was inserted
from the Lisp application's POV, so if you insist on having before and
after hooks to be called in pairs, you are in a conundrum.

It's possible that we should simplify all this by calling the before
hooks just once before the loop and the after hooks just once after
the loop, instead of calling them for each individual chunk inside the
loop, but again I don't know what that means for applications which
expects these hook calls to pair.

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