\version "2.19.44"

%% Thanks to David Nalesnik
%% http://lists.gnu.org/archive/html/lilypond-user/2016-07/msg00028.html

#(define create-stanza-number-grob-engraver
;; puts out a StanzaNumber for every LyricText-grob
  (lambda (context)
    (let ((stanza (ly:context-property context 'stanza)))
      `((acknowledgers
          (lyric-syllable-interface .
            ,(lambda (engraver grob source-engraver)
              (let ((new-stanza-grob 
                      (ly:engraver-make-grob engraver 'StanzaNumber '())))
              (ly:grob-set-property! new-stanza-grob 'text stanza)))))))))

#(define (at-line-beginning? grob)
   (let* ((col (ly:item-get-column grob))
          (ln (ly:grob-object col 'left-neighbor))
          (col-to-check (if (ly:grob? ln) ln col)))
     (and (eq? #t (ly:grob-property col-to-check 'non-musical))
          (= 1 (ly:item-break-dir col-to-check)))))

#(define (keep-at-line-begin grob)
   (if (and (ly:item? grob) (not (at-line-beginning? grob)))
       (ly:grob-suicide! grob)
       grob))

keepLineStartStanzaNumbers =
\layout {
  \context {
  \Lyrics
  \override StanzaNumber.after-line-breaking =
    #keep-at-line-begin
  }
}

numberLyrics =
#(define-scheme-function (nmbr)(number?)
"Return a context-modification setting @code{stanza} and consisting 
@code{create-stanza-number-grob-engraver}."
#{
  \with {
    stanza = \markup \italic #(format #f "~a." nmbr)
    \consists #create-stanza-number-grob-engraver
  }
#})