Avoid Scheme-computed Skyline_pair values to get collected before use

Retaining them as SCM values until they are no longer needed avoids
premature garbage collection.  This addresses circumstances in
connection with issue 3490.

diff --git a/lily/side-position-interface.cc b/lily/side-position-interface.cc
index dad906f51bf2cef85fcf9ac617d3cdc381a1b28d..8e23c2a03bb27734bfcd0b86afd9f42b43ca0025 100644 (file)
--- a/lily/side-position-interface.cc
+++ b/lily/side-position-interface.cc
@@ -214,14 +214,13 @@ Side_position_interface::aligned_side (Grob *me, Axis a, bool pure, int start, i
     common[Y_AXIS] = staff_symbol->common_refpoint (common[Y_AXIS], Y_AXIS);
 
   Skyline my_dim;
-  Skyline_pair *skyp = Skyline_pair::unsmob (
-                         me->get_maybe_pure_property (a == X_AXIS
-                                                      ? "horizontal-skylines"
-                                                      : "vertical-skylines",
-                                                      pure,
-                                                      start,
-                                                      end));
-  if (skyp)
+  SCM skyp = me->get_maybe_pure_property (a == X_AXIS
+                                          ? "horizontal-skylines"
+                                          : "vertical-skylines",
+                                          pure,
+                                          start,
+                                          end);
+  if (Skyline_pair::unsmob (skyp))
     {
       // for spanner pure heights, we don't know horizontal spacing,
       // so a spanner can never have a meaningful x coordiante
@@ -237,7 +236,7 @@ Side_position_interface::aligned_side (Grob *me, Axis a, bool pure, int start, i
       Real yc = a == X_AXIS
                 ? me->pure_relative_y_coordinate (common[Y_AXIS], start, end)
                 : me->get_parent (Y_AXIS)->maybe_pure_coordinate (common[Y_AXIS], Y_AXIS, pure, start, end);
-      Skyline_pair copy = Skyline_pair (*skyp);
+      Skyline_pair copy = *Skyline_pair::unsmob (skyp);
       copy.shift (a == X_AXIS ? yc : xc);
       copy.raise (a == X_AXIS ? xc : yc);
       my_dim = copy[-dir];
@@ -280,16 +279,15 @@ Side_position_interface::aligned_side (Grob *me, Axis a, bool pure, int start, i
         {
 
 
-           Skyline_pair *sp = Skyline_pair::unsmob
-             (e->get_maybe_pure_property (a == X_AXIS
-                                          ? "horizontal-skylines"
-                                          : "vertical-skylines",
-                                          pure || cross_staff,
-                                          start,
-                                          end));
+           SCM sp = e->get_maybe_pure_property (a == X_AXIS
+                                                ? "horizontal-skylines"
+                                                : "vertical-skylines",
+                                                pure || cross_staff,
+                                                start,
+                                                end);
 
            aligns_to_cross_staff |= cross_staff;
-           if (sp)
+           if (Skyline_pair::unsmob (sp))
              {
                Real xc = pure && dynamic_cast<Spanner *> (e)
                          ? e->get_parent (X_AXIS)->relative_coordinate (common[X_AXIS], X_AXIS)
@@ -299,7 +297,7 @@ Side_position_interface::aligned_side (Grob *me, Axis a, bool pure, int start, i
                Real yc = a == X_AXIS
                          ? e->pure_relative_y_coordinate (common[Y_AXIS], start, end)
                          : e->maybe_pure_coordinate (common[Y_AXIS], Y_AXIS, pure, start, end);
-               Skyline_pair copy = Skyline_pair (*sp);
+               Skyline_pair copy = *Skyline_pair::unsmob (sp);
                if (a == Y_AXIS
                    && Stem::has_interface (e)
                    && to_boolean (me->get_maybe_pure_property ("add-stem-support", pure, start, end)))