(mark_smob): don't mark parents, explain why.

[lilypond.git] / lily / break-substitution.cc

diff --git a/lily/break-substitution.cc b/lily/break-substitution.cc
index 73c24c20e5723fdd462220c828a38f1dac6fc5bf..4f560e85cd1c2b286b8e9106a0fc31e2a2442cb7 100644 (file)
--- a/lily/break-substitution.cc
+++ b/lily/break-substitution.cc
@@ -44,6 +44,15 @@ substitute_grob (Grob *sc)
       if (!line)
        return sc->self_scm();
 
+      /*
+       We don't return SCM_UNDEFINED for
+       suicided grobs, for two reasons
+
+       - it doesn't work (strange disappearing objects)
+
+       - it forces us to mark the parents of a grob, leading to
+       a huge recursion in the GC routine.
+       */
 
       /*
        This was introduced in 1.3.49 as a measure to prevent