[meld/deprecation-cleanup] ui._gtktemplate: Raise when we find unmatched callbacks

[Kai Willadsen <kaiw src gnome org>]

commit 0f5ed7da0b90fdeb3688dc0a75cbd140c1f53554
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Thu Dec 6 05:48:23 2018 +1000

    ui._gtktemplate: Raise when we find unmatched callbacks

 meld/ui/_gtktemplate.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/meld/ui/_gtktemplate.py b/meld/ui/_gtktemplate.py
index efaca339..e66c3b93 100644
--- a/meld/ui/_gtktemplate.py
+++ b/meld/ui/_gtktemplate.py
@@ -24,7 +24,9 @@ def connect_func(builder, obj, signal_name, handler_name,
                  connect_object, flags, cls):
 
     if handler_name not in cls.__gtktemplate_methods__:
-        return
+        raise RuntimeError(
+            "Handler '%s' was specified in template, but has no "
+            "matching @Gtk.Template.Callback" % handler_name)
 
     method_name = cls.__gtktemplate_methods__[handler_name]
     template_inst = builder.get_object(cls.__gtype_name__)