Fix some location xml handling to work with old session files.

Also refactor some code around it while I'm at it.

libs/ardour/location.cc

@@ -29,6 +29,7 @@
 #include "pbd/stl_delete.h"
 #include "pbd/xml++.h"
 #include "pbd/enumwriter.h"
+#include "pbd/statefulidpredicates.h"
 
 #include "ardour/location.h"
 #include "ardour/midi_scene_change.h"
@@ -610,6 +611,8 @@ Location::set_state (const XMLNode& node, int version)
 	}
 
 	if (!set_id (node)) {
+		// Old versions did not write ids for locations: make a new one.
+		reset_id();
 		warning << _("XML node for Location has no ID information") << endmsg;
 	}
 
@@ -1056,21 +1059,20 @@ Locations::set_state (const XMLNode& node, int version)
 
 			try {
 
+				Location* loc = 0;
 				XMLProperty const * prop_id = (*niter)->property ("id");
-				assert (prop_id);
-				PBD::ID id (prop_id->value ());
+				if (prop_id) {
+					LocationList::const_iterator i = std::find_if(
+						locations.begin(), locations.end(),
+						PBD::StatefulIdEquals(prop_id->value()));
 
-				LocationList::const_iterator i = locations.begin();
-				while (i != locations.end () && (*i)->id() != id) {
-					++i;
+					if (i != locations.end()) {
+						/* we can re-use an old Location object */
+						loc = *i;
+						loc->set_state (**niter, version);
+					}
 				}
-
-				Location* loc;
-				if (i != locations.end()) {
-					/* we can re-use an old Location object */
-					loc = *i;
-					loc->set_state (**niter, version);
-				} else {
+				if (!loc) {
 					loc = new Location (_session, **niter);
 				}
 

libs/pbd/pbd/statefulidpredicates.h

@@ -0,0 +1,59 @@
+/*
+    Copyright (C) 2015 Paul Davis 
+    Author: Sakari Bergen
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program 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 General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#ifndef __pbd_statefulidpredicate_h__
+#define __pbd_statefulidpredicate_h__
+
+#include "pbd/libpbd_visibility.h"
+#include "pbd/id.h"
+#include "pbd/stateful.h"
+
+namespace PBD {
+
+struct LIBPBD_TEMPLATE_MEMBER_API StatefulIdEquals
+{
+	StatefulIdEquals(ID const & id)
+	  : id(id)
+	{}
+
+	template<typename StatefulPtr>
+	bool operator() (StatefulPtr p)
+	{
+		return p && compare(*p);
+	}
+
+	bool operator() (Stateful const & s)
+	{
+		return compare(s);
+	}
+
+private:
+
+	bool compare(Stateful const & s)
+	{
+		return s.id() == id;
+	}
+
+	ID const & id;
+};
+
+} // namespace PBD
+
+#endif // __pbd_statefulidpredicate_h__