fix streett_to_generalized_buchi

Fixes #316.

* spot/twaalgos/totgba.cc: Fix confusing definition of scc_inf_wo_fin.
* tests/python/streett_totgba2.py: New test case.
* tests/Makefile.am: Add it.
* NEWS: Mention the bug.

NEWS

@@ -243,6 +243,10 @@ New in spot 2.4.4.dev (net yet released)
     set.  In spot 2.4.x this function was only used by autfilt
     --simplify-acceptance; in 2.5 it is now used in remove_fin().
 
+  - spot::streett_to_generalized_buchi() could generate incorrect
+    automata with empty language if some Fin set did not intersect all
+    accepting SCCs (in other words, the fix from 2.4.1 was incorrect).
+
   - ltlcross could crash when calling remove_fin() on an automaton
     with 32 acceptance sets would need an additional set.
 

spot/twaalgos/totgba.cc

@@ -556,6 +556,7 @@ namespace spot
         else
           inf_alone |= pair.inf;
 
+        if (pair.inf)
           for (unsigned mark: pair.inf.sets())
             inf_to_finpairs[mark] |= pair.fin;
       }
@@ -573,13 +574,19 @@ namespace spot
         auto acc_fin = acc & fin;     // {0,  2,  4,6}
         auto acc_inf = acc & inf;     // {  1,  3,    7,9}
         acc_cond::mark_t fin_wo_inf = 0U;
+        // Fin sets that are alone either because the acceptance
+        // condition has not matching Inf, or because the SCC the not
+        // intersect the matching inf.
         for (unsigned mark: acc_fin.sets())
           if (!fin_to_infpairs[mark] || (fin_to_infpairs[mark] - acc_inf))
             fin_wo_inf.set(mark);
 
+        // Inf sets that *do* have a matching Fin in the acceptance
+        // condition but without matching Fin in the SCC: they can be
+        // considered as always present in the SCC.
         acc_cond::mark_t inf_wo_fin = 0U;
-        for (unsigned mark: acc_inf.sets())
-          if (!inf_to_finpairs[mark] || (inf_to_finpairs[mark] - acc_fin))
+        for (unsigned mark: inf.sets())
+          if (inf_to_finpairs[mark] && (inf_to_finpairs[mark] - acc_fin))
             inf_wo_fin.set(mark);
 
         sccfi.emplace_back(fin_wo_inf, inf_wo_fin,
@@ -671,7 +678,7 @@ namespace spot
                 // If the acceptance is (Fin(0) | Inf(1)) & Inf(2)
                 // but we do not see any Fin set in this SCC, a
                 // mark {2} should become {1,2} before striping.
-                acc = (t.acc | (inf - scc_inf_wo_fin)).strip(to_strip);
+                acc = (t.acc | scc_inf_wo_fin).strip(to_strip);
               }
             assert((acc & out->acc().all_sets()) == acc);
 

tests/Makefile.am

@@ -388,6 +388,7 @@ TESTS_python = \
   python/setxor.py \
   python/simstate.py \
   python/streett_totgba.py \
+  python/streett_totgba2.py \
   python/rs_like.py \
   python/sum.py \
   python/trival.py \

tests/python/streett_totgba2.py

@@ -0,0 +1,70 @@
+#!/usr/bin/python3
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2018 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/>.
+
+import spot
+
+# Issue 316
+a = spot.automaton("""
+HOA: v1
+States: 8
+Start: 0
+AP: 3 "b" "a" "c"
+Acceptance: 5 (Fin(0) | Inf(1)) & (Fin(2) | Inf(3)) & Inf(4)
+properties: trans-labels explicit-labels state-acc
+--BODY--
+State: 0
+[!0&!2] 1
+[0&!2] 2
+[2] 3
+State: 1
+[0&2] 4
+[0&1&2] 5
+State: 2
+[!0&!2] 1
+[!0&2] 3
+State: 3
+[!0&!2] 1
+[!0&2] 3
+[0&2] 4
+[0&1&2] 5
+State: 4
+[2] 4
+[0&1&2] 5
+[!0&!2] 6
+State: 5 {4}
+[1&2] 5
+[!0&1&!2] 7
+State: 6
+[0&2] 4
+[0&1&2] 5
+State: 7 {1 3 4}
+[0&1&2] 5
+--END--
+""")
+
+tgba = spot.streett_to_generalized_buchi(a)
+assert tgba.acc().is_generalized_buchi()
+ba = spot.simplify_acceptance(a)
+assert ba.acc().is_buchi()
+
+nba = spot.dualize(ba.postprocess('generic', 'deterministic'))
+ntgba = spot.dualize(tgba.postprocess('generic', 'deterministic'))
+assert not ba.intersects(ntgba)
+assert not tgba.intersects(nba)