after change function not invoked on all changes in *Messages*

after change function not invoked on all changes in *Messages*

[Milan Zamazal]

In GNU Emacs 21.3.2 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2003-06-03 on blackbird, modified by Debian

When I try to install a local after change function on the *Messages*
buffer, it's not invoked on insertions to that buffer via the `message'
function and some other functions.  When I edit the buffer manually, the
after change function gets invoked as expected.  On deletions, the after
change function seems to be always invoked.

Try the following:

- Eval the following code:

   (defvar foo nil)
   (defun my-after-change (&rest args)
     (setq foo (cons args foo)))

- Switch to the *Messages* buffer.

- Apply

   `M-: (add-hook 'after-change-functions 'my-after-change nil t) RET'

- Apply

   `M-: (message "hello") RET'

- There's nothing about the `hello' insertion in the variable `foo'.

- Now try to type or yank some text in *Messages*.

- `foo' should contain information about the changes.

I couldn't find anything in documentation explaining this behavior, so I
think it's a bug.

Re: after change function not invoked on all changes in *Messages*

[Richard Stallman]

    When I try to install a local after change function on the *Messages*
    buffer, it's not invoked on insertions to that buffer via the `message'
    function and some other functions.

Messages are generated from places in the code where
it is not safe to call Lisp code, so the change hooks are
disabled.  I will document that.

Re: after change function not invoked on all changes in *Messages*

[Milan Zamazal]

>>>>> "RS" == Richard Stallman <rms@gnu.org> writes:

    RS> Messages are generated from places in the code where it is not
    RS> safe to call Lisp code, so the change hooks are disabled.  I
    RS> will document that.

OK, thank you.

Regards,

Milan Zamazal

-- 
All programmers are optimists.  Perhaps this modern sorcery especially attracts
those who believe in happy endings and fairy godmothers.  Perhaps the hundreds
of nitty frustrations drive away all but those who habitually focus on the end
goal.                     -- Frederick P. Brooks, Jr. in The Mythical Man-Month