From: Alan Mackenzie <acm@muc.de>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: (insert ?\n) spuriously calls before-change-functions twice. Help!
Date: Tue, 5 Jan 2010 17:31:58 +0000 [thread overview]
Message-ID: <20100105173158.GB2639@muc.de> (raw)
In-Reply-To: <jwvfx6ko9vw.fsf-monnier+emacs@gnu.org>
Hi, Stefan,
On Tue, Jan 05, 2010 at 10:22:26AM -0500, Stefan Monnier wrote:
> > In emacs -Q, in an AWK buffer, do M-: (insert ?\n). The following
> [...]
> > However, M-: (insert "\n") just does the Right Thing.
> That's curious indeed.
> > This second invocation of before-change-functions is surely a bug. I
> > can make this happen in a Fundamental Mode buffer in my normal Emacs
> > session, but not in Emacs -Q.
> Can you try to figure out which diference between "emacs -Q" and your
> "normal Emacs session" triggers the problem?
I think I've tracked down what's happening. After inserting the ?\n (any
other character is just the same), Emacs clears any text properties from
the new character by calling set_properties. This, in its turn, invokes
before-change-functions. A more detailed call stack is:
Finsert calls
general_insert_function (insert, insert_from_string, 0, nargs, args) calls
(*insert_func) (str, len), namely insert (str, len), calls
insert_1_both (string, len, nbytes, 0, 1, 0), calls
prepare_to_modify_buffer, calls
signal_before_change. This does the first invocation of b_c_f. <======
insert_1_both inserts the character ?\n into the buffer.
insert_1_both (conditionally on BUF_INTERVALS) calls
set_text_properties on the newly inserted character, calls
modify_region, calls
prepare_to_modify_buffer, calls
signal_before_change. This does the second invocation of
b_c_f. <=============================
There doesn't seem to be any system in where the two change hooks are
invoked. For example, insert directly calls signal_after_change, yet not
signal_before_change; surely invocations of these should be paired.
I think there needs to be two levels of these primitive: a "user level",
which invokes the change hooks, and calls the "internal level" to do the
actual work. Other primitives would call only the "internal level". Or
something like that.
For CC Mode, I will put in a test for two consecutive invocations of
before-change-functions without an after-change-functions between them.
In such a case, I then ignore the second invocation. I think.
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2010-01-05 17:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-05 11:09 (insert ?\n) spuriously calls before-change-functions twice. Help! Alan Mackenzie
2010-01-05 15:22 ` Stefan Monnier
2010-01-05 17:31 ` Alan Mackenzie [this message]
2010-01-05 19:52 ` Stefan Monnier
2010-01-06 13:05 ` Alan Mackenzie
2010-01-06 14:33 ` Stefan Monnier
2010-01-19 13:23 ` Alan Mackenzie
2010-01-19 15:11 ` Chong Yidong
2010-01-19 17:11 ` Alan Mackenzie
2010-01-19 18:02 ` Chong Yidong
2010-01-19 22:30 ` Alan Mackenzie
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