product: fix handling of operand with false acceptance

* NEWS: Mention the issue.
* spot/twaalgos/product.cc: Fix it.
* tests/python/prodexpt.py: Test it.

NEWS

@@ -91,6 +91,13 @@ New in spot 2.8.6.dev (not yet released)
   - car() is a new variant of LAR algorithm that combines several
     strategies for paritazing any automaton.
 
+  Bugs fixed:
+
+  - Building a product between two complete automata where one operand
+    had false acceptance could create a incomplete automaton
+    incorrectly tagged as complete, causing the print_hoa() function
+    to raise an exception.
+
 New in spot 2.8.6 (2020-02-19)
 
   Bugs fixed:

spot/twaalgos/product.cc

@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2014-2019 Laboratoire de Recherche et Développement
+// Copyright (C) 2014-2020 Laboratoire de Recherche et Développement
 // de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -285,21 +285,34 @@ namespace spot
       if (!res)                 // aborted
         return nullptr;
 
-      // The product of two non-deterministic automata could be
+      if (res->acc().is_f())
-      // deterministic.  Likewise for non-complete automata.
+        {
-      if (left->prop_universal() && right->prop_universal())
+          assert(res->num_edges() == 0);
-        res->prop_universal(true);
+          res->prop_universal(true);
-      if (left->prop_complete() && right->prop_complete())
+          res->prop_complete(false);
-        res->prop_complete(true);
+          res->prop_stutter_invariant(true);
-      if (left->prop_stutter_invariant() && right->prop_stutter_invariant())
+          res->prop_terminal(true);
-        res->prop_stutter_invariant(true);
+          res->prop_state_acc(true);
-      if (left->prop_inherently_weak() && right->prop_inherently_weak())
+        }
-        res->prop_inherently_weak(true);
+      else
-      if (left->prop_weak() && right->prop_weak())
+        {
-        res->prop_weak(true);
+          // The product of two non-deterministic automata could be
-      if (left->prop_terminal() && right->prop_terminal())
+          // deterministic.  Likewise for non-complete automata.
-        res->prop_terminal(true);
+          if (left->prop_universal() && right->prop_universal())
-      res->prop_state_acc(left->prop_state_acc() && right->prop_state_acc());
+            res->prop_universal(true);
+          if (left->prop_complete() && right->prop_complete())
+            res->prop_complete(true);
+          if (left->prop_stutter_invariant() && right->prop_stutter_invariant())
+            res->prop_stutter_invariant(true);
+          if (left->prop_inherently_weak() && right->prop_inherently_weak())
+            res->prop_inherently_weak(true);
+          if (left->prop_weak() && right->prop_weak())
+            res->prop_weak(true);
+          if (left->prop_terminal() && right->prop_terminal())
+            res->prop_terminal(true);
+          res->prop_state_acc(left->prop_state_acc()
+                              && right->prop_state_acc());
+        }
       return res;
     }
   }
@@ -450,6 +463,10 @@ namespace spot
             {
               auto res = make_twa_graph(left->get_dict());
               res->new_state();
+              res->prop_terminal(true);
+              res->prop_stutter_invariant(true);
+              res->prop_universal(true);
+              res->prop_complete(false);
               return res;
             }
           return make_twa_graph(left, twa::prop_set::all());

tests/python/prodexpt.py

@@ -1,6 +1,6 @@
 # -*- mode: python; coding: utf-8 -*-
-# Copyright (C) 2016-2017, 2019 Laboratoire de Recherche et Développement de
+# Copyright (C) 2016-2017, 2019-2020 Laboratoire de Recherche et Développement
-# l'Epita (LRDE).
+# de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
 #
@@ -102,3 +102,34 @@ res = spot.product(left, right, spot.output_aborter(900, 9000))
 assert res is None
 res = spot.product(left, right, spot.output_aborter(1000, 9000))
 assert res is not None
+
+a, b = spot.automata("""HOA: v1 States: 1 Start: 0 AP: 0 acc-name: all
+Acceptance: 0 t properties: trans-labels explicit-labels state-acc complete
+properties: deterministic stutter-invariant weak --BODY-- State: 0 [t] 0
+--END-- HOA: v1 States: 1 Start: 0 AP: 0 acc-name: none Acceptance: 0 f
+properties: trans-labels explicit-labels state-acc complete properties:
+deterministic stutter-invariant weak --BODY-- State: 0 [t] 0 --END--""")
+out = spot.product(a, b).to_str()
+assert out == """HOA: v1
+States: 1
+Start: 0
+AP: 0
+acc-name: none
+Acceptance: 0 f
+properties: trans-labels explicit-labels state-acc deterministic
+properties: stutter-invariant terminal
+--BODY--
+State: 0
+--END--"""
+out = spot.product_susp(a, b).to_str()
+assert out == """HOA: v1
+States: 1
+Start: 0
+AP: 0
+acc-name: all
+Acceptance: 0 t
+properties: trans-labels explicit-labels state-acc deterministic
+properties: stutter-invariant terminal
+--BODY--
+State: 0
+--END--"""