bug#63861: [PATCH] pp.el: New "pretty printing" code

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> BTW, how does this compare to the newly added `pp-emacs-lisp-code`?

Very good question.  I had completely missed that (and its `pp-use-max-width`).
This points to a host of integration issues between my code and the
existing code.  I'll have to take a deeper look.

> It was still rough around the edges the last time I set
> `pp-use-max-width' non-nil.  It is also quite a lot slower than the
> old path.

My new code is expected to be slower than the "normal" pretty-printer,
but barring performance bugs in `lisp-indent-line` (such as the one
fixed by the patch I just sent to Thierry) it should be approximately
a constant factor slower.

AFAICT the performance of `pp-emacs-lisp-code` can be more problematic.

Beside performance, I guess the behavior of the two should be
somewhat similar, tho I also see that `pp-emacs-lisp-code` pays
attention to the Edebug and `doc-string-elt` info, so it may give
slightly more refined info.

Another difference is that `pp-emacs-lisp-code` starts with an S-exp
object, whereas my code starts with a region (i.e. an sexp that's
already been printed).


        Stefan