Issue 1322 in lilypond: \context must die (whenever \new can be used instead)

[lilypond]

Status: Accepted
Owner: ----
Labels: Type-Documentation Priority-Medium Syntax

New issue 1322 by v.villenave: \context must die (whenever \new can be used  
instead)
http://code.google.com/p/lilypond/issues/detail?id=1322

There really are only two cases where \context is acceptable:
  - when introducing a block inside \layout { ... }
  - when referring to an existing, /explicitely named/ context.

The first case is off the table.

The second possibility, of course, is much less frequent/useful/used at  
all. Truth is, most of the time people use \context instead of \new without  
any good reason whatsoever, which leads to syntax inconsistencies.

The documentation isn't entirely clear either: for instance, NR  
5.1.2 "Creating contexts" has the following example
<<
  \new Staff \context Voice = "A" \music
  \context Voice = "A" \arts


where \new would be more appropriate when creating the Voice:
<<
  \new Staff \new Voice = "A" \music
  \context Voice = "A" \arts


Another example: NR 1.1.3.5 Automatic accidentals uses the following  
example:
\new PianoStaff {
  <<
    \context Staff = "up" {
      #(set-accidental-style 'default)
      \musicA
    }
    \context Staff = "down" {
      #(set-accidental-style 'default)
      \musicB
    }
  >>

It's also used a lot in LM snippets (templates, etc.).

---

It's not uncommon that users (particularly new users, or users who have  
been using older versions in the past, when the syntax was different)  
encounter problems (and ask for help) just because of that.  So we  
definitely need to:
  - discourage this syntax (unless specifically needed, which is quite  
advanced and pretty rare -- in fact, I've yet to see a case where it  
actually is)
  - clean up the docs/regtests (and possibly snippets), just like we did  
with \new Score.
  - I even wonder if a warning could be issued by convert-ly when it  
encounters \context outside of a \layout block?