Re: Improving representation of EIEIO objects in backtraces/error messages

[Eric Ludlam <eric@siege-engine.com>]

On 12/31/2016 03:48 PM, Eric Abrahamsen wrote:
> Eric Ludlam <eric@siege-engine.com> writes:
>
>> On 12/29/2016 02:02 PM, Eric Abrahamsen wrote:
...
>> CEDET includes a 'data-debug' package.  If you enable that it provides a
>> way to navigate giant data structures as you might get with EIEIO.  It
>> is also a part of Emacs now, though I'm not that familiar with how it
>> all was merged.
>>
>> I have this in my .emacs file to take advantage of it:
>>
>> (require 'data-debug)
>> (global-set-key "\M-:" 'data-debug-eval-expression)
>
> That's interesting, thanks! I'll play with it a bit, it might be nice to
> add the slot names in with the values.

The slot names should be included in the display.  At least they are for 
me in my older Emacs.  It may be that the eieio-support doesn't work 
quite right after the EIEIO change in Emacs?

In CEDET, eieio-datadebug is separate, but with EIEIO as a piece of core 
emacs with Data Debug, maybe the current tenuous load should be replaced 
by merging eieio-datadebug into data-debug.

...
>> In the CEDET repository, you can get cedet-edebug.el.  It includes
>> these two snippets that bind "A" to data debug.
>>
>> ;;;###autoload
>> (add-hook 'edebug-setup-hook
[...]

> These are all good for me as a developer, but I would also like to
> protect users from backtraces that might, ahem, arise from my code. Do
> you have any opinion on the discussion in
> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25295 ? Anything would be
> welcome.

I'm not familiar with Emacs C level expression printing.  That's why I 
just stopped using built ins and added my own top level commands to get 
things done.

The ideas represented in the thread where some special vector-form could 
fork off to a special printer sounds like a pretty nice idea though. 
That way more than just EIEIO objects could be simplified.

In the above thread, someone mentioned giving up an object's ability to 
customize it's print output.  This is a super handy feature where you 
can take some key differentiator of your object that is short to put 
into the short form print output.  Taking advantage of that feature 
makes using the short print output even better.  Of course, the 
developer needs to implement the method to make it work.  I usually go 
add a new print-object method when I'm debugging so I can figure out 
what's going on.

Eric