From 2df973cc940e9bf1862579a80a2f94a009c8f621 Mon Sep 17 00:00:00 2001
From: David Kastrup <dak@gnu.org>
Date: Sat, 4 Jun 2016 17:41:23 +0200
Subject: [PATCH] Issue 4997/4: Use Preinit in Spanner

---
 lily/include/spanner.hh |  3 ++-
 lily/spanner.cc         | 23 +++++++++++++++++------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/lily/include/spanner.hh b/lily/include/spanner.hh
index 79032dfb30..bc41ec6e63 100644
--- a/lily/include/spanner.hh
+++ b/lily/include/spanner.hh
@@ -39,7 +39,7 @@
     is absolutely necessary for beams, since they have to adjust the
     length of stems of notes they encompass.
 */
-class Spanner : public Grob
+class Spanner : public Preinit<Spanner>, public Grob
 {
   Drul_array<Item *> spanned_drul_;
   vsize break_index_;
@@ -66,6 +66,7 @@ public:
   void set_bound (Direction d, Grob *);
   Item *get_bound (Direction d) const;
 
+  void pre_init ();
   Spanner (SCM);
   Spanner (Spanner const &);
   bool is_broken () const;
diff --git a/lily/spanner.cc b/lily/spanner.cc
index 3f3d17fb27..1b6798086a 100644
--- a/lily/spanner.cc
+++ b/lily/spanner.cc
@@ -224,19 +224,27 @@ Spanner::set_bound (Direction d, Grob *s)
     Pointer_group_interface::add_grob (i, ly_symbol2scm ("bounded-by-me"), this);
 }
 
+void
+Spanner::pre_init ()
+{
+  break_index_ = (vsize)-1;
+  // This is stupid, but derived_mark may be run before broken_into_
+  // has run its constructor and has a recognizable array size.
+  // So we use break_index_ == -1 as a sentinel.
+  spanned_drul_.set (0, 0);
+  pure_property_cache_ = SCM_UNDEFINED;
+}
+
 Spanner::Spanner (SCM s)
   : Grob (s)
 {
   break_index_ = 0;
-  spanned_drul_.set (0, 0);
-  pure_property_cache_ = SCM_UNDEFINED;
 }
 
 Spanner::Spanner (Spanner const &s)
   : Grob (s)
 {
-  spanned_drul_.set (0, 0);
-  pure_property_cache_ = SCM_UNDEFINED;
+  break_index_ = 0;
 }
 
 /*
@@ -341,8 +349,11 @@ Spanner::derived_mark () const
       scm_gc_mark (spanned_drul_[d]->self_scm ());
   ;
 
-  for (vsize i = broken_intos_.size (); i--;)
-    scm_gc_mark (broken_intos_[i]->self_scm ());
+  // If break_index_ is -1, broken_intos_ might not yet have run its
+  // constructor and any access might break things.
+  if (break_index_ != (vsize)-1)
+    for (vsize i = broken_intos_.size (); i--;)
+      scm_gc_mark (broken_intos_[i]->self_scm ());
 }
 
 /*
-- 
2.39.2