Do not output empty parse error blocks in the CGI script.

* wrap/python/spot.i: Provide a __nonzero__() method for
parse_error_list.
* wrap/python/cgi-bin/ltl2tgba.in: Do not call format_parse_errors()
unconditionally.

ChangeLog

+2011-01-17  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Do not output empty parse error blocks in the CGI script.
+
+	* wrap/python/spot.i: Provide a __nonzero__() method for
+	parse_error_list.
+	* wrap/python/cgi-bin/ltl2tgba.in: Do not call format_parse_errors()
+	unconditionally.
+
 2011-01-12  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	Fix "unused function" warnings reported by clang++.

wrap/python/cgi-bin/ltl2tgba.in

@@ -497,9 +497,10 @@ pel = spot.empty_parse_error_list()
 f = spot.parse(formula, pel, env, show_parse)
 if show_parse: print '</pre>'
 
-print '<font color="red"><pre>'
-err = spot.format_parse_errors(spot.get_cout(), formula, pel)
-print '</pre></font>'
+if pel:
+    print '<font color="red"><pre>'
+    err = spot.format_parse_errors(spot.get_cout(), formula, pel)
+    print '</pre></font>'
 
 if not f:
     print '<p><b>Aborting...</b></p>'

wrap/python/spot.i

@@ -280,3 +280,13 @@ unblock_signal(int signum)
 }
 
 %}
+
+%extend spot::ltl::parse_error_list {
+
+bool
+__nonzero__()
+{
+  return !self->empty();
+}
+
+}