>From 2cf7db9ee6d7bfdfa9358a889b6210f2b71cb6dd Mon Sep 17 00:00:00 2001
From: Mark Knoop <address@hidden>
Date: Thu, 28 Jul 2016 15:47:46 +0100
Subject: [PATCH] Keep a staff alive if any other staff in the group is alive

This uses the `VerticalAxisGroup.remove-layer' property, when set to -1, to keep
the context alive within a `Keep_alive_together_engraver' only while any other
context is alive, even if those contexts have `VerticalAxisGroup.remove-layer'
set to false.
---
 input/regression/keep-alive-with-any-other.ly | 56 +++++++++++++++++++++++++++
 lily/keep-alive-together-engraver.cc          |  8 +++-
 2 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 input/regression/keep-alive-with-any-other.ly

diff --git a/input/regression/keep-alive-with-any-other.ly b/input/regression/keep-alive-with-any-other.ly
new file mode 100644
index 0000000..ecc4868
--- /dev/null
+++ b/input/regression/keep-alive-with-any-other.ly
@@ -0,0 +1,56 @@
+\version "2.19.47"
+
+\header {
+  texidoc = "The @code{VerticalAxisGroup.remove-layer} property can be set to
+  @code{-1} to keep it alive only while any other VerticalAxisGroup layer
+  controlled by the same Keep_alive_together_engraver is alive."
+}
+
+\score {
+  <<
+    \new StaffGroup \with {
+      \consists Keep_alive_together_engraver
+    } <<
+      \new Staff \with {
+        keepAliveInterfaces = #'()
+        instrumentName = "With 2 or 3"
+        shortInstrumentName = "w"
+		    \override VerticalAxisGroup.remove-empty = ##t
+		    \override VerticalAxisGroup.remove-first = ##t
+        \override VerticalAxisGroup.remove-layer = -1
+      } {
+        \repeat unfold 200 c''4
+      }
+      \new Staff \with {
+        instrumentName = "2"
+        shortInstrumentName = "2"
+		    \override VerticalAxisGroup.remove-empty = ##t
+		    \override VerticalAxisGroup.remove-first = ##t
+        \override VerticalAxisGroup.remove-layer = ##f
+      } {
+        \repeat unfold 20 c'4
+        R1*20
+        \repeat unfold 20 c'4
+        R1*20
+      }
+      \new Staff \with {
+        instrumentName = "3"
+        shortInstrumentName = "3"
+		    \override VerticalAxisGroup.remove-empty = ##t
+		    \override VerticalAxisGroup.remove-first = ##t
+        \override VerticalAxisGroup.remove-layer = ##f
+      } {
+        R1*10
+        \repeat unfold 40 c'4
+        \repeat unfold 40 c'4
+        R1*20
+      }
+    >>
+    \new Staff \with {
+      instrumentName = "Continuous"
+      shortInstrumentName = "c"
+    } {
+      \repeat unfold 200 g'4
+    }
+  >>
+}
diff --git a/lily/keep-alive-together-engraver.cc b/lily/keep-alive-together-engraver.cc
index 9b1cbe4..5125854 100644
--- a/lily/keep-alive-together-engraver.cc
+++ b/lily/keep-alive-together-engraver.cc
@@ -64,12 +64,18 @@ Keep_alive_together_engraver::finalize ()
         {
           if (i == j)
             continue;
+          if (scm_is_integer (this_layer) and (scm_to_int (this_layer) == -1))
+            {
+              // if remove-layer == -1, layer is kept alive by any other layer
+              live->add (group_spanners_[j]);
+              continue;
+            }
           SCM that_layer = group_spanners_[j]->get_property ("remove-layer");
           if (scm_is_false (that_layer))
             continue;
           if (!scm_is_integer (this_layer))
             {
-              // Unspecified layers are kept alive by anything else
+              // unspecified layers are kept alive by all but ignored layers
               live->add (group_spanners_[j]);
               continue;
             }
-- 
2.7.4