From dd7a75b0862bf05adec8033a1c4a15f225255101 Mon Sep 17 00:00:00 2001
From: David Kastrup <dak@gnu.org>
Date: Mon, 20 Feb 2012 18:39:23 +0100
Subject: [PATCH] Add layout changing command \layout-from for getting context
 defs from music

---
 input/regression/layout-from.ly | 19 ++++++++
 ly/context-mods-init.ly         | 77 ++++++++++++++++++++++++++++++++-
 2 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 input/regression/layout-from.ly

diff --git a/input/regression/layout-from.ly b/input/regression/layout-from.ly
new file mode 100644
index 0000000000..2c0669a2fe
--- /dev/null
+++ b/input/regression/layout-from.ly
@@ -0,0 +1,19 @@
+\version "2.15.31"
+
+\header {
+  texidoc = "
+@code{\\layout-from} can interpret property-setting music for changing
+context definitions inside of layout definitions like @code{\\layout}
+or @code{\\midi}.
+"
+}
+
+\score {
+  \relative c' { cis cis cis cis }
+  \layout {
+    \layout-from { \accidentalStyle "dodecaphonic" }
+  }
+  \midi {
+    \layout-from { \tempo 4 = 240 }
+  }
+}
diff --git a/ly/context-mods-init.ly b/ly/context-mods-init.ly
index 087d4bb155..b8361a58ec 100644
--- a/ly/context-mods-init.ly
+++ b/ly/context-mods-init.ly
@@ -16,7 +16,7 @@
 %%%% You should have received a copy of the GNU General Public License
 %%%% along with LilyPond.  If not, see <http://www.gnu.org/licenses/>.
 
-\version "2.15.6"
+\version "2.15.31"
 
 RemoveEmptyStaves = \with {
   \remove "Axis_group_engraver"
@@ -31,3 +31,78 @@ RemoveEmptyStaves = \with {
   \description "Remove staves which are considered to be empty according
 to the list of interfaces set by @code{keepAliveInterfaces}."
 }
+
+"layout-from" =
+#(define-void-function (parser location bottom music)
+   ((symbol? 'Voice) ly:music?)
+   (_i "To be used in output definitions.  Take the layout instruction
+events from @var{music} and do the equivalent of context modifications
+duplicating their effect.
+
+This is handy for making layout definitions by using property
+definitions like @code{\\accidentalStyle} or definitions like
+@code{\\tabFullNotation} that may work in multiple or unknown
+contexts.
+
+Layout instructions specified without explicit context get mapped to
+the context symbol @var{bottom}, with a default of @code{'Voice}.
+
+For example, you can tell @code{\\layout-from} to apply a contained
+@example
+\\override #'font-size = #2
+@end example
+to @samp{TabVoice} or @samp{Lyrics} context instead of the default
+@samp{Voice} context, if the context where you would normally use
+@var{music} is not one that would have @samp{Voice} as its
+@samp{Bottom}.")
+   (let loop ((m music) (mods #f))
+     ;; The parser turns all sets, overrides etc into something
+     ;; wrapped in ContextSpeccedMusic.  If we ever get a set,
+     ;; override etc that is not wrapped in ContextSpeccedMusic, the
+     ;; user has created it in Scheme himself without providing the
+     ;; required wrapping.  In that case, using #f in the place of a
+     ;; context modification results in a reasonably recognizable
+     ;; error.
+     (if (music-is-of-type? m 'layout-instruction-event)
+	 (ly:add-context-mod
+	  mods
+	  (case (ly:music-property m 'name)
+	    ((PropertySet)
+	     (list 'assign
+		   (ly:music-property m 'symbol)
+		   (ly:music-property m 'value)))
+	    ((PropertyUnset)
+	     (list 'unset
+		   (ly:music-property m 'symbol)))
+	    ((OverrideProperty)
+	     (list 'push
+		   (ly:music-property m 'symbol)
+		   (ly:music-property m 'grob-property-path)
+		   (ly:music-property m 'grob-value)))
+	    ((RevertProperty)
+	     (list 'pop
+		   (ly:music-property m 'symbol)
+		   (ly:music-property m 'grob-property-path)))))
+	 (case (ly:music-property m 'name)
+	   ((SequentialMusic SimultaneousMusic)
+	    (fold loop mods (ly:music-property m 'elements)))
+	   ((ContextSpeccedMusic)
+	    ;; It is actually rather embarrassing that we have no
+	    ;; reliable way to check for the type of a context-def.
+	    ;; Nor have a Scheme way to add to a context-def.
+	    (let ((sym (ly:music-property m 'context-type)))
+	      (if (eq? sym 'Bottom)
+		  (set! sym bottom))
+	      (if (module-bound? (current-module) sym)
+		  (module-set!
+		   (current-module)
+		   sym
+		   #{ \context {
+				 $(module-ref (current-module) sym)
+				 $(loop (ly:music-property m 'element)
+					(ly:make-context-mod))
+		      }
+		   #})
+		  (ly:warning music (_f "Cannot find context-def \\~a"
+					sym)))))))
+     mods))
-- 
2.39.2