Re: Extended bar checking?

[Jean Abou Samra]

Le 18/09/2022 à 20:32, Mats Bengtsson a écrit :
> Hi,
>
> I've been pondering about a missing feature in LilyPond, namely the 
> possibility to get a warning printout if there isn't an explicit bar 
> check ("|") in the input file at the end of each measure. This would 
> catch many of the typos I personally do when entering music, where I 
> happen to forget to change a duration, or enter the wrong duration, so 
> that the current default duration happens to be, say, double the 
> correct duration.
>
> Example: Let's say I want to type
>
> \relative c' {
> c4 d e2 |
> g1 |
> g4 f e d |
> c1
> }
> but forget to add the duration "4" in the third measure:\relative c' {
> c4 d e2 |
> g1 |
> g f e d |
> c1
> }
> Obviously, this will not give any bar check warning, but if there was 
> a possibility to get a warning also for missing bar checks, I would 
> immediately catch those mistakes. This feature should not be on by 
> default, but for those of us who consequently add bar checks in the 
> input files, it would be extremely helpful.
>
> In another email thread today, Valentine provided an implementation of 
> a Bar_check_warning_egraver is somewhat along the same lines, but that 
> unfortunatly fails to catch the typo in the above example since it 
> only detects notes  where the duration crosses a bar line. As far as I 
> can see, the idea of Valentine's implementation cannot easily be 
> extended to do what I'm after and it's not immediately obvious to me 
> how hard it would be to implement it. Perhaps some of you clever 
> LilyPond hackers on the list have an idea, otherwise I will send it as 
> a feature request to the bug list.




Yes, it can be done.



\version "2.23.13"

#(define-event-class 'event 'StreamEvent) % cough

"|" = { | #(make-music 'Event 'is-bar-check #t) }

#(define (Require_bar_check_engraver context)
   (let ((heard #f)
         (previous-rhythmic-ev #f)
         (now-rhythmic-ev #f))
     (make-engraver
      (listeners
       ((event engraver event)
        (when (ly:event-property event 'is-bar-check #f)
          (set! heard #t)))
       ((rhythmic-event engraver event)
        (set! now-rhythmic-ev event)))
      ((stop-translation-timestep engraver)
       (when (and (not heard)
                  (ly:context-property context 'measureStartNow #f))
         (if previous-rhythmic-ev
             (ly:event-warning previous-rhythmic-ev "missing bar check 
after this note/rest")
             ;; maybe \skip <music>, for which it is hard to get a location
             (ly:warning "missing bar check at end of measure ~a"
                         (1- (ly:context-property context 
'currentBarNumber)))))
       (set! heard #f)
       (set! previous-rhythmic-ev now-rhythmic-ev)
       (set! now-rhythmic-ev #f)))))

\layout {
  \context {
    \Voice
    \consists #Require_bar_check_engraver
  }
}


\relative c' {
  c4 d e2 |
  g1 |
  g f e d | % notes wrongly entered
  s1 % missing bar check
  \skip {
    c1 % missing bar check
    c1
  } |
}




However, be aware of the limitations. This only checks that
in each voice, there is a bar check at every measure end.
It does not check that every component of the music generating
this voice has this bar check. For example, this gets accepted
without warning:

\new Voice << { c'1 | d' | e' | } { e'1 f' g' } >>


To my knowledge, it's not possible to also warn about this one without
some serious modifications in LilyPond's internals.

Jean