twa: do not set prop_state_acc in set_acceptance

Reported by Juraj Major.

* spot/twa/twa.hh: check num_sets() in prop_state_acc() so we do not
have to set it in set_acceptance(), causing trouble if set_acceptance()
is called multiple times.
* tests/python/setacc.py: New test case.
* tests/Makefile.am: Add it.
* THANKS: Add Juraj.
* NEWS: Mention the bug.

NEWS

@@ -66,6 +66,10 @@ New in spot 2.1.2.dev (not yet released)
   * remove_fin() could produce incorrect result on incomplete
     automata tagged as weak and deterministic.
 
+  * calling set_acceptance() several time on an automaton could result
+    in unexpected behaviors, because set_acceptance(0,...)  used to
+    set the state-based acceptance flag automatically.
+
 New in spot 2.1.2 (2016-10-14)
 
   Command-line tools:

THANKS

@@ -18,6 +18,7 @@ Jan Strejček
 Jean-Michel Couvreur
 Jean-Michel Ilié
 Joachim Klein
+Juraj Major
 Kristin Y. Rozier
 Martin Dieguez Lodeiro
 Matthias Heizmann

spot/twa/twa.hh

@@ -879,17 +879,12 @@ namespace spot
     {
       set_num_sets_(num);
       acc_.set_acceptance(c);
-      if (num == 0)
-        prop_state_acc(true);
     }
 
     /// Copy the acceptance condition of another TωA.
     void copy_acceptance_of(const const_twa_ptr& a)
     {
       acc_ = a->acc();
-      unsigned num = acc_.num_sets();
-      if (num == 0)
-        prop_state_acc(true);
     }
 
     /// Copy the atomic propositions of another TωA
@@ -915,8 +910,6 @@ namespace spot
     {
       set_num_sets_(num);
       acc_.set_generalized_buchi();
-      if (num == 0)
-        prop_state_acc(true);
     }
 
     /// \brief Set Büchi acceptance.
@@ -1092,6 +1085,8 @@ namespace spot
     /// the acceptance set.
     trival prop_state_acc() const
     {
+      if (num_sets() == 0)
+        return true;
       return is.state_based_acc;
     }
 

tests/Makefile.am

@@ -341,6 +341,7 @@ TESTS_python = \
   python/relabel.py \
   python/remfin.py \
   python/satmin.py \
+  python/setacc.py \
   python/setxor.py \
   python/trival.py \
   $(TESTS_ipython)

tests/python/setacc.py

@@ -0,0 +1,26 @@
+#!/usr/bin/python3
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2016 Laboratoire de Recherche et Développement de
+# l'EPITA.
+#
+# This file is part of Spot, a model checking library.
+#
+# Spot 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 3 of the License, or
+# (at your option) any later version.
+#
+# Spot 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, see <http://www.gnu.org/licenses/>.
+
+# Test case reduced from a report from Juraj Major <major@fi.muni.cz>.
+import spot
+a = spot.make_twa_graph(spot._bdd_dict)
+a.set_acceptance(0, spot.acc_code("t"))
+a.set_acceptance(1, spot.acc_code("Fin(0)"))
+assert(a.prop_state_acc() == 0);