Some thoughts on narrowing, was Re: How to compile Lilypond files using Emacs?

[David Wright]

On Mon 27 Jul 2020 at 17:02:15 (+1000), Andrew Bernard wrote:

> The issue is not WIndows specific. You need to add a line similar to
> this in your emacs init file to get the compile to work:
> 
> ;; lilypond
> (setq LilyPond-lilypond-command "lilypond -I ~/lib/lilypond
> -I~/lib/openlilylib/snippets")
> 
> I also add the following:
> 
> (autoload 'LilyPond-mode "lilypond-mode" "LilyPond Editing Mode" t)
> (add-to-list 'auto-mode-alist '("\\.ly$" . LilyPond-mode))
> (add-to-list 'auto-mode-alist '("\\.ily$" . LilyPond-mode))
> 
> But as said, you will run into issues with narrowing, and nested
> tuplets smash the formatting badly.

I can't say I agree with every indentation decision that LP/emacs
makes, but personally, the effects tend to be very shortlived,
ie lasting just a few lines. (My scores are much simpler than yours.)

As for narrowing, I wrote in 2015 that I'd not met the problem for
years, and that would be compatible with my installing Debian/squeeze
in March 2011. There's a note in lisp/simple.el that the default
value of blink-matching-paren-distance was increased from 25 to
100k with emacs version 23.2. At that time, none of my scores were
as big as 100kB.

Looking at site-lisp/lilypond-indent.el (which has changes quite
recently, though not in this area), it does appear that the
narrow-to-region call should be protected. My guess would be
that the call should be written as:

    (save-excursion
      (save-restriction
        (when blink-matching-paren-distance               ← line 501/502
          (narrow-to-region
           (max (point-min) (- (point) blink-matching-paren-distance))
           (min (point-max) (+ (point) blink-matching-paren-distance))))))

I've based that on the corresponding part of lisp/simple.el's:

            (save-excursion                               ← line 7571
              (save-restriction
                (if blink-matching-paren-distance
                    (narrow-to-region
                     (max (minibuffer-prompt-end) ;(point-min) unless minibuf.
                          (- (point) blink-matching-paren-distance))
                     oldpos))
                … … ))

(AFAICT the section marked … … does not exist in site-lisp/lilypond-indent.el.)

> As mentioned, search the archives of this list. There is quite a lot
> of discussion about this topic. I'd love to fix the issues, but my
> elisp-fu is not powerful enough I'm afraid.

Assuming that LP is getting its default value for blink-matching-paren-distance
from /usr/share/emacs/26.1/lisp/simple.el.gz (Debian/buster), I would
imagine that the definition could be overwritten in one's own startup
file. This could be as simple as inserting these lines, with a greater
value in place of 100.

(defcustom blink-matching-paren-distance (* 100 1024)
  "If non-nil, maximum distance to search backwards for matching open-paren.
If nil, search stops at the beginning of the accessible portion of the buffer."
  :version "23.2"                       ; 25->100k
  :type '(choice (const nil) integer)
  :group 'paren-blinking)

Apologies for my similar lack of elisp-fu.

Cheers,
David.