Glib: NodeTree etc.: Use callback functions with C linkage

* glib/glibmm/class.cc: Use glibmm_custom_[get|set]_property_callback().
* glib/glibmm/object.[cc|h]: Add set_data_with_c_callback().
Don't call g_object_set_qdata_full() with a function with C++ linkage, if
GLIBMM_CAN_ASSIGN_NON_EXTERN_C_FUNCTIONS_TO_EXTERN_C_CALLBACKS is defined.
* glib/glibmm/property.[cc|h]: Declare some local functions extern "C".
Add glibmm_custom_[get|set]_property_callback().
* glib/src/nodetree.[ccg|hg]:
Add glibmm_NodeTree_c_callback_[traverse|foreach]() and
struct NodeTreeCallback[Traverse|Foreach]Data.
Part of issue #1

7 files changed, 144 insertions, 17 deletions

diff --git a/glib/glibmm/class.cc b/glib/glibmm/class.cc
index 5344f381..1080f1ce 100644
--- a/glib/glibmm/class.cc
+++ b/glib/glibmm/class.cc
@@ -233,8 +233,8 @@ Class::custom_class_init_function(void* g_class, void* class_data)
   (*init_func)(g_class, nullptr);
 
   GObjectClass* const gobject_class = static_cast<GObjectClass*>(g_class);
-  gobject_class->get_property = &Glib::custom_get_property_callback;
-  gobject_class->set_property = &Glib::custom_set_property_callback;
+  gobject_class->get_property = &Glib::glibmm_custom_get_property_callback;
+  gobject_class->set_property = &Glib::glibmm_custom_set_property_callback;
 
   // Call extra class init functions, if any.
   for (std::size_t i = 1; i < class_init_funcs.size(); ++i)
@@ -277,7 +277,8 @@ Class::custom_class_init_function(void* g_class, void* class_data)
 
       // Override only properties which have not been overridden in a base class.
       // Store the default values belonging to the class.
-      // They are copied to an object in custom_set_property_callback() in property.cc.
+      // They are copied to an object in glibmm_custom_set_property_callback()
+      // in property.cc.
       if (!g_object_class_find_property(gobject_class, prop_name))
       {
         GValue* g_value = g_new0(GValue, 1);
diff --git a/glib/glibmm/object.cc b/glib/glibmm/object.cc
index 4dc73b31..30703d7d 100644
--- a/glib/glibmm/object.cc
+++ b/glib/glibmm/object.cc
@@ -283,10 +283,26 @@ Object::set_data(const Quark& id, void* data)
 }
 
 void
+Object::set_data_with_c_callback(const Quark& id, void* data, GDestroyNotify destroy)
+{
+  g_object_set_qdata_full(gobj(), id, data, destroy);
+}
+
+#ifdef GLIBMM_CAN_ASSIGN_NON_EXTERN_C_FUNCTIONS_TO_EXTERN_C_CALLBACKS
+void
 Object::set_data(const Quark& id, void* data, DestroyNotify destroy)
 {
   g_object_set_qdata_full(gobj(), id, data, destroy);
 }
+#else
+void
+Object::set_data(const Quark& id, void* data, DestroyNotify)
+{
+  g_object_set_qdata(gobj(), id, data);
+  g_critical("Can't assign a callback with C++ linkage to g_object_set_qdata_full().\n"
+             "Use Glib::Object::set_data_with_c_callback().\n");
+}
+#endif
 
 void
 Object::remove_data(const QueryQuark& id)
diff --git a/glib/glibmm/object.h b/glib/glibmm/object.h
index 6db4b5cb..4cb6ad91 100644
--- a/glib/glibmm/object.h
+++ b/glib/glibmm/object.h
@@ -33,7 +33,7 @@
 #include <glibmm/utility.h> /* Could be private, but that would be tedious. */
 #include <glibmm/containerhandle_shared.h> /* Because its specializations may be here. */
 #include <glibmm/value.h>
-#include <glib.h> /* for G_GNUC_NULL_TERMINATED */
+#include <glib.h> // for G_GNUC_NULL_TERMINATED and GDestroyNotify
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
 extern "C" {
@@ -118,12 +118,14 @@ public:
 
   // GObject* gobj_copy(); //Give a ref-ed copy to someone. Use for direct struct access.
 
-  // Glib::Objects contain a list<Quark, pair<void*, DestroyNotify> >
-  // to store run time data added to the object at run time.
-  // TODO: Use slots instead:
+  // TODO: When we can break ABI and API, remove DestroyNotify and the
+  // set_data() that uses it. Rename set_data_with_c_callback() to set_data().
   void* get_data(const QueryQuark& key);
   void set_data(const Quark& key, void* data);
   using DestroyNotify = void (*)(gpointer data);
+  /** @newin{2,78} */
+  void set_data_with_c_callback(const Quark& key, void* data, GDestroyNotify notify);
+  /** Prefer set_data_with_c_callback() with a callback with C linkage. */
   void set_data(const Quark& key, void* data, DestroyNotify notify);
   void remove_data(const QueryQuark& quark);
   // same as remove without notifying
diff --git a/glib/glibmm/property.cc b/glib/glibmm/property.cc
index 56dad849..6cb5f317 100644
--- a/glib/glibmm/property.cc
+++ b/glib/glibmm/property.cc
@@ -61,8 +61,10 @@ namespace
 // a) Almost all conceivable use-cases are supported by this approach.
 // b) It's comparatively efficient, and does not need a hash-table lookup.
 
+extern "C"
+{
 // Delete the interface property values when an object of a custom type is finalized.
-void
+static void
 destroy_notify_obj_iface_props(void* data)
 {
   auto obj_iface_props = static_cast<Glib::Class::iface_properties_type*>(data);
@@ -76,6 +78,7 @@ destroy_notify_obj_iface_props(void* data)
     delete obj_iface_props;
   }
 }
+} // extern "C"
 
 struct custom_properties_type
 {
@@ -92,8 +95,10 @@ struct custom_properties_type
 static const GQuark custom_properties_quark =
   g_quark_from_string("gtkmm_CustomObject_custom_properties");
 
+extern "C"
+{
 // Delete the custom properties data when an object of a custom type is finalized.
-void destroy_notify_obj_custom_props(void* data)
+static void destroy_notify_obj_custom_props(void* data)
 {
   auto obj_custom_props = static_cast<custom_properties_type*>(data);
   // prop_base_vector does not own the objects pointed to.
@@ -106,6 +111,7 @@ void destroy_notify_obj_custom_props(void* data)
   }
   delete obj_custom_props;
 }
+} // extern "C"
 
 custom_properties_type*
 get_obj_custom_props(GObject* obj)
@@ -125,11 +131,30 @@ get_obj_custom_props(GObject* obj)
 
 namespace Glib
 {
-
 void
 custom_get_property_callback(
   GObject* object, unsigned int property_id, GValue* value, GParamSpec* param_spec)
 {
+  glibmm_custom_get_property_callback(object, property_id, value, param_spec);
+}
+
+void
+custom_set_property_callback(
+  GObject* object, unsigned int property_id, const GValue* value, GParamSpec* param_spec)
+{
+  glibmm_custom_set_property_callback(object, property_id, value, param_spec);
+}
+
+extern "C"
+{
+// A function with external linkage and C linkage does not get a mangled name.
+// Even though glibmm_custom_get_property_callback() and glibmm_custom_set_property_callback()
+// are declared in a named namespace, the linker does not see the namespace name.
+// Therefore the function names shall have a prefix, hopefully unique.
+void
+glibmm_custom_get_property_callback(
+  GObject* object, unsigned int property_id, GValue* value, GParamSpec* param_spec)
+{
   // If the id is zero there is no property to get.
   g_return_if_fail(property_id != 0);
 
@@ -185,7 +210,7 @@ custom_get_property_callback(
 }
 
 void
-custom_set_property_callback(
+glibmm_custom_set_property_callback(
   GObject* object, unsigned int property_id, const GValue* value, GParamSpec* param_spec)
 {
   // If the id is zero there is no property to set.
@@ -262,6 +287,7 @@ custom_set_property_callback(
     }
   }
 }
+} // extern "C"
 
 /**** Glib::PropertyBase ***************************************************/
 
diff --git a/glib/glibmm/property.h b/glib/glibmm/property.h
index daf92eca..5f553ccf 100644
--- a/glib/glibmm/property.h
+++ b/glib/glibmm/property.h
@@ -26,6 +26,7 @@ namespace Glib
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
 
+// TODO: When we can break ABI, remove custom_[get|set]_property_callback().
 #ifdef GLIBMM_CXX_CAN_USE_NAMESPACES_INSIDE_EXTERNC
 // For the AIX xlC compiler, I can not find a way to do this without putting the functions in the
 // global namespace. murrayc
@@ -44,6 +45,18 @@ void custom_set_property_callback(
 } // extern "C"
 #endif // GLIBMM_CXX_CAN_USE_NAMESPACES_INSIDE_EXTERNC
 
+extern "C"
+{
+GLIBMM_API
+void glibmm_custom_get_property_callback(
+  GObject* object, unsigned int property_id, GValue* value, GParamSpec* param_spec);
+
+GLIBMM_API
+void glibmm_custom_set_property_callback(
+  GObject* object, unsigned int property_id, const GValue* value, GParamSpec* param_spec);
+
+} // extern "C"
+
 #endif /* DOXYGEN_SHOULD_SKIP_THIS */
 
 /** This is the base class for Glib::Object properties.
@@ -109,10 +122,10 @@ protected:
 private:
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
 
-  friend void Glib::custom_get_property_callback(
+  friend void Glib::glibmm_custom_get_property_callback(
     GObject* object, unsigned int property_id, GValue* value, GParamSpec* param_spec);
 
-  friend void Glib::custom_set_property_callback(
+  friend void Glib::glibmm_custom_set_property_callback(
     GObject* object, unsigned int property_id, const GValue* value, GParamSpec* param_spec);
 
 #endif /* DOXYGEN_SHOULD_SKIP_THIS */
diff --git a/glib/src/nodetree.ccg b/glib/src/nodetree.ccg
index 6ee2218c..dbfc52e5 100644
--- a/glib/src/nodetree.ccg
+++ b/glib/src/nodetree.ccg
@@ -1 +1,39 @@
+/* Copyright (C) 2007 glibmm development team
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
 #include <glibmm/nodetree.h>
+
+namespace Glib
+{
+extern "C"
+{
+// A function with external linkage and C linkage does not get a mangled name.
+// Even though glibmm_NodeTree_c_callback_traverse() and glibmm_NodeTree_c_callback_foreach()
+// are declared in a named namespace, the linker does not see the namespace name.
+// Therefore the function names shall have a prefix, hopefully unique.
+gboolean glibmm_NodeTree_c_callback_traverse(GNode* node, gpointer data)
+{
+  auto traverse_data = reinterpret_cast<NodeTreeCallbackTraverseData*>(data);
+  return (*traverse_data->func)(node, traverse_data->data);
+}
+
+void glibmm_NodeTree_c_callback_foreach(GNode* node, gpointer data)
+{
+  auto foreach_data = reinterpret_cast<NodeTreeCallbackForeachData*>(data);
+  (*foreach_data->func)(node, foreach_data->data);
+}
+} // extern "C"
+} // namespace Glib
diff --git a/glib/src/nodetree.hg b/glib/src/nodetree.hg
index 300b7f31..62353574 100644
--- a/glib/src/nodetree.hg
+++ b/glib/src/nodetree.hg
@@ -29,6 +29,33 @@ _DEFS(glibmm,glib)
 
 namespace Glib
 {
+#ifndef DOXYGEN_SHOULD_SKIP_THIS
+extern "C"
+{
+/// Wrapper for invoking a TraverseFunc.
+gboolean glibmm_NodeTree_c_callback_traverse(GNode* node, gpointer data);
+
+/// Wrapper for invoking a ForeachFunc.
+void glibmm_NodeTree_c_callback_foreach(GNode* node, gpointer data);
+
+} // extern "C"
+
+// Like GNodeTraverseFunc and GNodeForeachFunc, but with C++ linkage.
+using NodeTreeCallbackTraverseFuncType = gboolean (*)(GNode *node, gpointer user_data);
+using NodeTreeCallbackForeachFuncType = void (*)(GNode *node, gpointer user_data);
+
+struct NodeTreeCallbackTraverseData
+{
+  NodeTreeCallbackTraverseFuncType func;
+  gpointer data;
+};
+
+struct NodeTreeCallbackForeachData
+{
+  NodeTreeCallbackForeachFuncType func;
+  gpointer data;
+};
+#endif /* DOXYGEN_SHOULD_SKIP_THIS */
 
 /** N-ary Trees - trees of data with any number of branches
  * The NodeTree class and its associated functions provide an N-ary tree data structure, in which nodes in the tree can contain arbitrary data.
@@ -300,7 +327,8 @@ public:
   void traverse(const TraverseFunc& func, TraverseType order = TraverseType::IN_ORDER, TraverseFlags flags = TraverseFlags::ALL, int max_depth = -1)
   {
     TraverseFunc func_copy = func;
-    g_node_traverse(gobj(), (GTraverseType)order, (GTraverseFlags)flags, max_depth, c_callback_traverse, reinterpret_cast<gpointer>(&func_copy));
+    NodeTreeCallbackTraverseData traverse_data = { &c_callback_traverse, &func_copy };
+    g_node_traverse(gobj(), (GTraverseType)order, (GTraverseFlags)flags, max_depth, glibmm_NodeTree_c_callback_traverse, &traverse_data);
   }
   _IGNORE(g_node_traverse);
 
@@ -313,7 +341,8 @@ public:
   void foreach(const ForeachFunc& func, TraverseFlags flags = TraverseFlags::ALL)
   {
     ForeachFunc func_copy = func;
-    g_node_children_foreach(gobj(), (GTraverseFlags)flags, c_callback_foreach, reinterpret_cast<gpointer>(&func_copy));
+    NodeTreeCallbackForeachData foreach_data = { &c_callback_foreach, &func_copy };
+    g_node_children_foreach(gobj(), (GTraverseFlags)flags, glibmm_NodeTree_c_callback_foreach, &foreach_data);
   }
   _IGNORE(g_node_children_foreach)
 
@@ -331,7 +360,8 @@ public:
     using type_foreach_gnode_slot = sigc::slot<void(GNode*)>;
     type_foreach_gnode_slot bound_slot = sigc::bind(real_slot, the_data, &child);
 
-    g_node_children_foreach(gobj(), (GTraverseFlags)flags, c_callback_foreach_compare_child, reinterpret_cast<gpointer>(&bound_slot));
+    NodeTreeCallbackForeachData foreach_data = { &c_callback_foreach_compare_child, &bound_slot };
+    g_node_children_foreach(gobj(), (GTraverseFlags)flags, glibmm_NodeTree_c_callback_foreach, &foreach_data);
 
     return wrap(child);
   }
@@ -365,7 +395,8 @@ public:
     using type_traverse_gnode_slot = sigc::slot<gboolean(GNode*)>;
     type_traverse_gnode_slot bound_slot = sigc::bind(real_slot, the_data, &child);
 
-    g_node_traverse(const_cast<GNode*>(gobj()), (GTraverseType)order, (GTraverseFlags)flags, -1, c_callback_traverse_compare_node, reinterpret_cast<gpointer>(&bound_slot));
+    NodeTreeCallbackTraverseData traverse_data = { &c_callback_traverse_compare_node, &bound_slot };
+    g_node_traverse(const_cast<GNode*>(gobj()), (GTraverseType)order, (GTraverseFlags)flags, -1, glibmm_NodeTree_c_callback_traverse, &traverse_data);
 
     return wrap(child);
   }