Re: font-lock and shell scripts: Raises redisplay errors in highlight pattern:

[T. V. Raman]

Here are some more details on this problem.

The error is definitely being raised -- but also caught by the
condition-case  handler in functions
font-lock-default-fontify-buffer and
font-lock-default-fontify-region.

The condition-case in those functions means that
toggle-debug-on-error does not give a backtrace alas.

But I am able to reliably trigger it as follows:

Open an empty file and put it in sh-mode.

Type:

#!/bin/bash
export a=1

You see the error immediately after you hit the ' ' after the
keyword "export".

The error being raised  (from searching the font-lock.el sources,
it's one of the font-lock-apply-* functions)
Error during redisplay: (error No match 6 in highlight (6
font-lock-builtin-face))



So two questions:

1) Might be marginally benefitial even for the mainstream emacs user
to not have these errors raised and handled --
--- what variables in my sh-mode/font-lock environment should I
look at to chase down and fix the cause of the error in the first
place? (Note that I'm running with font-lock turned on at the
highest level).

2) And I'll possibly file this as a separate bug report once
   Stephane elaborates on what he said toward the end of his
   note:


How can I tell programmatically at run time if an error that is
raised has a handler somewhere above in the call stack waiting to
handle it?

If I had (2), then my advice  on error could be smart in the
following way:

When (error ...) is called:

Before-Advice:

A)      Check if there is a handler waiting to catch the error.
B)      If yes, do nothing;
C) Else give the user auditory feedback.

I could achieve an equivalent effect if I  knew how to check the
following in elisp:

Check if an error has "bubbled" all the way up the call stack.



Note that I have to advice error in Emacspeak because too many
useful Emacs packages use (error ...) to signal useful
information ---as an example, VM (the mail reader I use)
uses error to signal end of folder.


would be nice if 

>>>>> "Stefan" == Stefan Monnier <address@hidden> writes:
    >> One possibility is that I'm noticing these errors when
    >> others dont because I advice 'error in emacspeak to get
    >> auditory alerts for errors.  Since 'error does not return,
    >> this has to be a before advice.  A side-consequence of
    >> this is that errors that are later by an error-handler
    >> further up the call stack end up still getting signaled
    >> auditorally.
    Stefan> 
    Stefan> Please post a feature request with M-x
    Stefan> report-emacs-bug: it should be possible to customize
    Stefan> the top-level handling of errors (currently hardcoded
    Stefan> in cmd_error_internal).
    Stefan> 
    Stefan> 
    Stefan>         Stefan

 Thanks, 
 --Raman

-- 
Best Regards,
--raman

      
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