Re: command-error-function default handler

[Jarek Czekalski]

W dniu 2013-10-27 04:44, Stefan Monnier pisze:
> The way to do that right is as follows:
> - change command-error-function's default value to not be nil.
> - don't set command-error-function via `setq' but via `add-function'.
> The first step may require changes to the C code.

Now I noticed that in current state of Emacs command-error-function may 
not be used by a package. Only user can use it. If a package grabs it, 
no other package can use it. So no package at all may grab it as a result.

A cumbersome workaround is possible. If the value is nil, create a first 
handler with standard output included. If the value is not nil (there is 
already other handler), do add-function and don't produce standard 
output. But this is a workaround, not a reasonable usage of the feature.

In the meantime I probably found the answer to my question. Looking at 
usage of print_error_message in other files I came up with something 
that resembles the default handler behaviour:

(defun test-handler (&optional conditions context source)
  (message "%s%s: %s" context source (error-message-string conditions))
  ; we would also like to ring a bell here
)

So this is probably something that could be added to docs. Still this 
feature is not yet useful for packages. A package is the place where I 
wanted to use it. See related bug report: 15670 [1]

If I am wrong, please correct me.

Jarek

[1] http://debbugs.gnu.org/cgi/bugreport.cgi?bug=15670