genem: improve handling of co-Büchi

* spot/twaalgos/sccinfo.cc, spot/twaalgos/sccinfo.hh: Make sure
scc_and_mark_filter does not install a filter if there is nothing
to filter.
* tests/python/genem.py, spot/twaalgos/genem.cc,
python/spot/impl.i: Adjust.

python/spot/impl.i

@@ -654,7 +654,7 @@ def state_is_accepting(self, src) -> "bool":
 %noexception spot::scc_info::edges_of;
 %noexception spot::scc_info::inner_edges_of;
 %rename(scc_info_with_options) spot::scc_info::scc_info(const_twa_graph_ptr aut, scc_info_options options);
-%rename(scc_info_with_options) spot::scc_info::scc_info(scc_and_mark_filter& filt, scc_info_options options);
+%rename(scc_info_with_options) spot::scc_info::scc_info(const scc_and_mark_filter& filt, scc_info_options options);
 
 %include <spot/twaalgos/sccinfo.hh>
 %template(scc_info_scc_edges) spot::internal::scc_edges<spot::digraph<spot::twa_graph_state, spot::twa_graph_edge_data> const, spot::internal::keep_all>;

spot/twaalgos/genem.cc

@@ -108,9 +108,8 @@ namespace spot
             }
           return true;
         }
-      // FIXME: If there is acc.fin_unit() it, is
+      scc_info si(scc_and_mark_filter(aut, aut_acc.fin_unit()),
-      // probably a good idea to filter right away.
+                  scc_info_options::STOP_ON_ACC);
-      scc_info si(aut, scc_info_options::STOP_ON_ACC);
 
       const int accepting_scc = si.one_accepting_scc();
       if (accepting_scc >= 0)

spot/twaalgos/sccinfo.cc

@@ -75,9 +75,10 @@ namespace spot
     };
   }
 
-  scc_info::scc_info(scc_and_mark_filter& filt, scc_info_options options)
+  scc_info::scc_info(const scc_and_mark_filter& filt, scc_info_options options)
     : scc_info(filt.get_aut(), filt.start_state(),
-               filt.get_filter(), &filt, options)
+               filt.get_filter(),
+               const_cast<scc_and_mark_filter*>(&filt), options)
   {
   }
 

spot/twaalgos/sccinfo.hh

@@ -457,12 +457,12 @@ namespace spot
     /// This is usually used to prevent some edges from being
     /// considered as part of cycles, and can additionally restrict
     /// to exploration to some SCC discovered by another SCC.
-    scc_info(scc_and_mark_filter& filt, scc_info_options options);
+    scc_info(const scc_and_mark_filter& filt, scc_info_options options);
     // we separate the two functions so that we can rename
     // scc_info(x,options) into scc_info_with_options(x,options) in Python.
     // Otherwrise calling scc_info(aut,options) can be confused with
     // scc_info(aut,initial_state).
-    scc_info(scc_and_mark_filter& filt)
+    scc_info(const scc_and_mark_filter& filt)
     : scc_info(filt, scc_info_options::ALL)
     {
     }
@@ -814,9 +814,13 @@ namespace spot
       return aut_->get_init_state_number();
     }
 
-    scc_info::edge_filter get_filter()
+    scc_info::edge_filter get_filter() const
     {
-      return lower_si_ ? filter_scc_and_mark_ : filter_mark_;
+      if (lower_si_)
+        return filter_scc_and_mark_;
+      if (cut_sets_)
+        return filter_mark_;
+      return nullptr;
     }
   };
 

tests/python/genem.py

@@ -207,6 +207,9 @@ def is_scc_empty1(si, scc_num, acc=None):
     return True
 
 def is_empty2(g):
+    return is_empty2_rec(spot.scc_and_mark_filter(g, g.acc().fin_unit()))
+
+def is_empty2_rec(g):
     si = spot.scc_info_with_options(g, spot.scc_info_options_STOP_ON_ACC)
     if si.one_accepting_scc() >= 0:
         return False
@@ -224,13 +227,13 @@ def is_scc_empty2(si, scc_num, acc=None):
     acc = acc.restrict_to(occur)
     acc = acc.remove(common, False)
     # 3 stop conditions removed here, because they are caught by
-    # one_accepting_scc() or is_rejecting_scc() in is_empty2()
+    # one_accepting_scc() or is_rejecting_scc() in is_empty2_rec()
     for cl in acc.top_disjuncts():
         fu = cl.fin_unit() # Is there Fin at the top level
         if fu:
             with spot.scc_and_mark_filter(si, scc_num, fu) as filt:
                 filt.override_acceptance(cl.remove(fu, True))
-                if not is_empty1(filt):
+                if not is_empty2_rec(filt):
                     return False
         else:
             # Pick some Fin term anywhere in the formula
@@ -238,7 +241,7 @@ def is_scc_empty2(si, scc_num, acc=None):
             # Try to solve assuming Fin(fo)=True
             with spot.scc_and_mark_filter(si, scc_num, [fo]) as filt:
                 filt.override_acceptance(cl.remove([fo], True))
-                if not is_empty2(filt):
+                if not is_empty2_rec(filt):
                     return False
             # Try to solve assuming Fin(fo)=False
             if not is_scc_empty2(si, scc_num, acc.force_inf([fo])):