\version "2.17.0"
\paper {
  ragged-right = ##t
}
\relative c'' {
  \override Score.DynamicTextSpanner #'style = #'none
  % a cresc that ends in the same line is okay
  c1\cresc | c c\! | 
  % but a cresc immediately before a line break will trigger a 
  % warning about the line-spanner ending before it started, even 
  % though we don't use any visible spanner:
  c\cresc |\break
  c\!
}