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bug#36566: 27.0.50; debug is sometimes horribly slow

From: Michael Heerdegen
Subject: bug#36566: 27.0.50; debug is sometimes horribly slow
Date: Mon, 15 Jul 2019 04:05:07 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

Gemini Lasswell <address@hidden> writes:

> The easy fix for you for today is to set backtrace-line-length to 100 or
> less, which will make the initial values of print-length and print-level
> so low that little reprinting will be done.  Then use
> backtrace-expand-ellipsis (bound to "."), with or without C-u, on the
> lines where you want to see the full data structure.  And try "+" and
> "-" if you haven't already.

Ok, will have a look at these commands.  I've simply turned print-gensym
off for now in the debugger.

> I'll experiment with tweaking the heuristic to reduce the amount of
> reprinting it does, and let you know what I come up with.

Ok, great, tia.  Dunno if it would be worth it to optimize this test
printing, e.g. by turning print-gensym temporarily off.

> > BTW, extra points if the debugger provided commands/ a menu to tune such
> > settings (like printing variables) live when using it.
> There is such a command for print-circle (bound to "#") and it would be
> easy to add one for print-gensym, although I could use a keybinding
> suggestion.

You could use ":".  Or "# #" for print-circle and "# :" for print-gensym
(i.e. make "#" a prefix command).  This is inspired by print-circle
references looking like #N# and print syntax of gensyms looking like

In any case, _please_ add both to the menu for discoverability, maybe
also the "global" version (i.e. 4 entries in sum).

BTW, when I eval this

(let ((x '#1=(1 . #1#)))
  (cons x x))

I get a backtrace like

Debugger entered: nil
  (let ((x '(1 . #6))) (debug) (cons x x))
  eval((let ((x '(1 . #7))) (debug) (cons x x)) t)

whereby when I hit C-u # all references get number 1, or start from 1
for every frame:

Debugger entered: nil
  (let ((x '#1=(1 . #1#))) (debug) (cons x x))
  eval((let ((x '#1=(1 . #1#))) (debug) (cons x x)) t)

Just a minor inconvenience, though.

Anyway, thanks for improving the debugger in this way so far, this is
very useful.


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