genem: fix removal of unsatisfied Fin(x) sets

Fixes #360.

* spot/twa/acc.cc, spot/twa/acc.hh (force_inf): New method.
* spot/twaalgos/genem.cc: Fix the emptiness check using force_inf.
* tests/python/genem.py: Add test case and adjust the python
version of the emptiness check.

spot/twa/acc.cc

@@ -1481,6 +1481,51 @@ namespace spot
       SPOT_UNREACHABLE();
       return {};
     }
+
+    static acc_cond::acc_code
+    force_inf_rec(const acc_cond::acc_word* pos, acc_cond::mark_t rem)
+    {
+      auto start = pos - pos->sub.size;
+      switch (pos->sub.op)
+        {
+        case acc_cond::acc_op::And:
+          {
+            --pos;
+            auto res = acc_cond::acc_code::t();
+            do
+              {
+                auto tmp = force_inf_rec(pos, rem) & std::move(res);
+                std::swap(tmp, res);
+                pos -= pos->sub.size + 1;
+              }
+            while (pos > start);
+            return res;
+          }
+        case acc_cond::acc_op::Or:
+          {
+            --pos;
+            auto res = acc_cond::acc_code::f();
+            do
+              {
+                auto tmp = force_inf_rec(pos, rem) | std::move(res);
+                std::swap(tmp, res);
+                pos -= pos->sub.size + 1;
+              }
+            while (pos > start);
+            return res;
+          }
+        case acc_cond::acc_op::Fin:
+          return acc_cond::acc_code::fin(pos[-1].mark - rem);
+        case acc_cond::acc_op::Inf:
+          return acc_cond::acc_code::inf(pos[-1].mark);
+        case acc_cond::acc_op::FinNeg:
+        case acc_cond::acc_op::InfNeg:
+          SPOT_UNREACHABLE();
+          return {};
+        }
+      SPOT_UNREACHABLE();
+      return {};
+    }
   }
 
   acc_cond::acc_code
@@ -1499,6 +1544,14 @@ namespace spot
     return strip_rec(&back(), rem, missing, false);
   }
 
+  acc_cond::acc_code
+  acc_cond::acc_code::force_inf(mark_t rem) const
+  {
+    if (is_t() || is_f())
+      return *this;
+    return force_inf_rec(&back(), rem);
+  }
+
   acc_cond::mark_t
   acc_cond::acc_code::used_sets() const
   {

spot/twa/acc.hh

@@ -921,6 +921,8 @@ namespace spot
       acc_code remove(acc_cond::mark_t rem, bool missing) const;
       // Same as remove, but also shift numbers
       acc_code strip(acc_cond::mark_t rem, bool missing) const;
+      // for all x in m, this replaces Fin(x) by false.
+      acc_code force_inf(mark_t m) const;
 
       // Return the set of sets appearing in the condition.
       acc_cond::mark_t used_sets() const;
@@ -1388,6 +1390,12 @@ namespace spot
         { num_sets() - (all_sets() & rem).count(), code_.strip(rem, missing) };
     }
 
+    // For all x in m, this replaces Fin(x) by false.
+    acc_cond force_inf(mark_t m) const
+    {
+      return {num_sets(), code_.force_inf(m)};
+    }
+
     // Restrict an acceptance condition to a subset of set numbers
     // that are occurring at some point.
     acc_cond restrict_to(mark_t rem) const

spot/twaalgos/genem.cc

@@ -175,7 +175,7 @@ namespace spot
            <deal_with_disjunct>))
         return false;
       // Try to accept when Fin(fo) == false
-      tmp.set(acc.remove({(unsigned) fo}, false));
+      tmp.set(acc.force_inf({(unsigned) fo}));
       return generic_emptiness_check_for_scc_nocopy
         <deal_with_disjunct>(si, scc, tocut);
       return true;