Getting complete Lisp backraces - the difficulty thereof

[Alan Mackenzie <acm@muc.de>]

Hello Emacs.

Why is it so difficult to get complete Lisp backtraces?

It seems as though Emacs does its level best to discard large amounts of
data from backtraces no matter what one does.  This is frustrating.

Why is there not a single variable to be set for this purpose?  Instead,
there are, perhaps, 20 - 30 controlling variables, all of whom seem set
to discard information by default.  These are things like print-level,
eval-expression-print-leval, edebug-print-level, cl-print-depth,
ert-batch-print-level, ert-batch-backtrace-right-margin, and on and on
and on.

These variables, collectively, are ridiculous.  It is unreasonable to
expect users to master them, the precious differences between them.  Each
of them, taken individually, may seem to be justified, but the collection
as a whole is lamentable.

Personally, I have given up trying to use these variables.  I just go to
the source code (e.g. ert.el), and spend time editing it to use
debug-early rather than debug, setting variables to "infinite" where they
allow it, and such things.

I don't think it's possible to set ert to output complete backtraces, no
matter what one does.  By default one gets tiny amounts of data truncated
to 70 columns wide, utterly useless for debugging.

On a related note, some recent change has caused several copies of the
12-character string "\342\200\246" to be displayed in some lines of my
backtraces.  This appears to be an attempt to write U2026, the ellipsis,
to my terminal.  This is something I never asked for, neither the 12
character string nor the ellipsis itself, and I haven't been able to find
any directions in NEWS or the ChangeLog to restore the old behaviour.

The state of these things in Emacs is not good.

-- 
Alan Mackenzie (Nuremberg, Germany).