[goffice] GocGroup: minimally support of ->children.

[Morten Welinder <mortenw src gnome org>]

commit 8b92b6cb4f3ae7f7037e87f9a3fae9da8e8ee006
Author: Morten Welinder <terra gnome org>
Date:   Tue Jun 16 19:30:01 2020 -0400

    GocGroup: minimally support of ->children.

 goffice/canvas/goc-group.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
---
diff --git a/goffice/canvas/goc-group.c b/goffice/canvas/goc-group.c
index ee8570b7..0e9ae68b 100644
--- a/goffice/canvas/goc-group.c
+++ b/goffice/canvas/goc-group.c
@@ -364,6 +364,18 @@ goc_group_clear (GocGroup *group)
        goc_group_freeze (group, TRUE);
 }
 
+// Provide just enough of the old ->children fields that it can be used
+// to test for empty and inspection of only child.
+static void
+goc_group_fake_xchildren (GocGroup *group)
+{
+       g_list_free (group->Xchildren);
+       group->Xchildren = group->priv->children
+               ? g_list_prepend (NULL, goc_group_get_child (group, 0))
+               : NULL;
+}
+
+
 /**
  * goc_group_add_child:
  * @parent: #GocGroup
@@ -393,6 +405,8 @@ goc_group_add_child (GocGroup *parent, GocItem *item)
        item->parent = parent;
        item->canvas = parent->base.canvas;
 
+       goc_group_fake_xchildren (parent);
+
        /* Notify of changes.  */
        if (old_canvas && item->canvas != old_canvas)
                _goc_canvas_remove_item (old_canvas, item);
@@ -430,6 +444,7 @@ goc_group_remove_child (GocGroup *parent, GocItem *item)
        g_ptr_array_remove_index (parent->priv->children, n);
        item->parent = NULL;
        item->canvas = NULL;
+       goc_group_fake_xchildren (parent);
        g_object_notify (G_OBJECT (item), "parent");
        g_object_notify (G_OBJECT (item), "canvas");
        goc_item_bounds_changed (GOC_ITEM (parent));