Tech data accessible as "technology-data" config value

Previously, the "technology-data" complex configuration
value was stored in the configuration file, but not
accessible from scripts through Application#set_config
and Applicatiob#get_config. It was as pseudo parameter
that wasn't dynamically connected to the application
state.

Now it's handled separately as if it was a normal
parameter. This is just an intermediate solution
required because this interface is the only one
through which tech data is accessible from scripts.

src/lay/layApplication.cc

@@ -1639,7 +1639,22 @@ void
 Application::set_config (const std::string &name, const std::string &value)
 {
   if (mp_plugin_root) {
-    mp_plugin_root->config_set (name, value);
+
+    if (name == cfg_technologies) {
+
+      //  HACK: cfg_technologies is not a real configuration parameter currently. Hence we emulate that
+      //  behavior. But currently this is the only way to access technology data indirectly from a script.
+      //  Note that this method will set only the technologies accessible through the configuration parameter.
+      //  I.e. the ones not auto-imported.
+      //  TODO: rework this one. This is only half-hearted.
+      if (! value.empty ()) {
+        lay::Technologies::instance ()->load_from_xml (value);
+      }
+
+    } else {
+      mp_plugin_root->config_set (name, value);
+    }
+
   }
 }
 
@@ -1655,7 +1670,16 @@ std::string
 Application::get_config (const std::string &name) const
 {
   if (mp_plugin_root) {
-    return mp_plugin_root->config_get (name);
+    if (name == cfg_technologies) {
+      //  HACK: cfg_technologies is not a real configuration parameter currently. Hence we emulate that
+      //  behavior. But currently this is the only way to access technology data indirectly from a script.
+      //  Note that this method will return only the technologies accessible through the configuration parameter.
+      //  I.e. the ones not auto-imported.
+      //  TODO: rework this one.
+      return lay::Technologies::instance ()->to_xml ();
+    } else {
+      return mp_plugin_root->config_get (name);
+    }
   } else {
     return std::string ();
   }

src/laybasic/layTechnology.cc

@@ -97,9 +97,19 @@ Technologies::to_xml () const
 void 
 Technologies::load_from_xml (const std::string &s)
 {
+  //  create a copy to filter out the ones which are not persisted and remain
+  lay::Technologies copy;
+  for (const_iterator t = begin (); t != end (); ++t) {
+    if (! t->is_persisted ()) {
+      copy.add (new Technology (*t));
+    }
+  }
+
   tl::XMLStringSource source (s);
   tl::XMLStruct<lay::Technologies> xml_struct ("technologies", xml_elements ());
-  xml_struct.parse (source, *this);
+  xml_struct.parse (source, copy);
+
+  *this = copy;
 }
 
 void