Re: [Lilypond-auto] Issue 2981 in lilypond: Bugs with \set Staff.whichBar

[lilypond]

Comment #1 on issue 2981 by address@hidden: Bugs with \set  
Staff.whichBar
http://code.google.com/p/lilypond/issues/detail?id=2981

'whichBar  is a strange property.  Actually, the strange thing is that the  
Default_bar_line_engraver continually sets and resets this property,  
whereas most properties will stay at the values given by the \set command  
in user input.

It would be nice to use whichBar in a less-strange manner, but that would  
be a big change because of the way whichBar is checked for possible  
line-breaks.

The place in the documentation that says '\set Staff.whichBar = "|:" will  
create a
start-repeat bar in this staff only'  is in the Internals Reference section  
on Default_bar_line_engraver, auto-generated  
from 'define-grob-properties.scm', so we should only expect it to work when  
we also move the engraver to the Staff context:
<< { c' \set Staff.whichBar = "||" c' c' c' }
  { c' \once \set Staff.whichBar = "||" c' c' c' c' c' c' c' } >>
\layout {
  \context { \Staff \consists "Default_bar_line_engraver" }
  \context { \Score \remove "Default_bar_line_engraver" } }

I suggest adding ".. if the engraver is in the Staff context" to that line  
in the documentation.

The version above with \once\set Staff.whichBar did work as the  
bug-reporter suggested, until the fix for issue 153.   Maybe we could have  
\once\set Context.property restore the original value (keeping issue 153  
correct) but *only* if there was an original value in the specified context.

I would rather ask users (like me) to use \set and \unset pairs for this  
strange case.

Attachments:
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