autfilt: Add --is-terminal and --is-weak.

Fixes #47.

* src/twaalgos/strength.cc, src/twaalgos/strength.hh
(is_weak_automaton): New function.
(is_terminal_automaton): Generalize slightly.
* src/bin/autfilt.cc: Add options --is-terminal and --is-weak.
* src/tests/readsave.test: Add a test.
* NEWS: Update.

src/twaalgos/strength.cc

@@ -19,49 +19,68 @@
 
 #include "strength.hh"
 #include "misc/hash.hh"
+#include "isweakscc.hh"
 #include <deque>
 
 namespace spot
 {
+  namespace
+  {
+    template <bool terminal>
+    bool is_type_automaton(const const_twa_graph_ptr& aut, scc_info* si)
+    {
+      // Create an scc_info if the user did not give one to us.
+      bool need_si = !si;
+      if (need_si)
+	si = new scc_info(aut);
+      si->determine_unknown_acceptance();
+
+      bool result = true;
+      unsigned n = si->scc_count();
+      for (unsigned i = 0; i < n; ++i)
+	{
+	  if (si->is_trivial(i))
+	    continue;
+	  bool first = true;
+	  acc_cond::mark_t m = 0U;
+	  for (auto src: si->states_of(i))
+	    for (auto& t: aut->out(src))
+	      if (si->scc_of(t.dst) == i)
+		{
+		  if (first)
+		    {
+		      first = false;
+		      m = t.acc;
+		    }
+		  else if (m != t.acc)
+		    {
+		      result = false;
+		      goto exit;
+		    }
+		}
+	  if (terminal && si->is_accepting_scc(i) && !is_complete_scc(*si, i))
+	    {
+	      result = false;
+	      break;
+	    }
+	}
+    exit:
+      if (need_si)
+	delete si;
+      return result;
+    }
+  }
+
   bool
   is_terminal_automaton(const const_twa_graph_ptr& aut, scc_info* si)
   {
-    if (aut->prop_terminal())
-      return true;
-    // Create an scc_info if the user did not give one to us.
-    bool need_si = !si;
-    if (need_si)
-      si = new scc_info(aut);
-    si->determine_unknown_acceptance();
+    return aut->prop_terminal() || is_type_automaton<true>(aut, si);
+  }
 
-    bool result = true;
-
-    for (auto& scc: *si)
-      {
-	if (scc.is_rejecting())
-	  continue;
-	// Accepting SCCs should have only one state.
-	auto& st = scc.states();
-	if (st.size() != 1)
-	  {
-	    result = false;
-	    break;
-	  }
-	// The state should have only one edge that is a
-	// self-loop labelled by true.
-	auto src = st.front();
-	auto out = aut->out(src);
-	auto it = out.begin();
-	assert(it != out.end());
-	result =
-	  (it->cond == bddtrue) && (it->dst == src) && (++it == out.end());
-	if (!result)
-	  break;
-      }
-
-    if (need_si)
-      delete si;
-    return result;
+  bool
+  is_weak_automaton(const const_twa_graph_ptr& aut, scc_info* si)
+  {
+    return aut->prop_weak() || is_type_automaton<false>(aut, si);
   }
 
   bool is_safety_mwdba(const const_twa_graph_ptr& aut)

src/twaalgos/strength.hh

@@ -25,9 +25,8 @@ namespace spot
 {
   /// \brief Whether an automaton is terminal.
   ///
-  /// An automaton is terminal if any accepting path ends on an
-  /// accepting state with only one transition that is a self-loop
-  /// labelled by true.
+  /// An automaton is terminal if it is weak, and all accepting SCCs
+  /// are complete.
   ///
   /// \param aut the automaton to check
   ///
@@ -36,6 +35,19 @@ namespace spot
   SPOT_API bool
   is_terminal_automaton(const const_twa_graph_ptr& aut, scc_info* sm = nullptr);
 
+
+  /// \brief Whether an automaton is weak.
+  ///
+  /// An automaton is weak if if any given SCC, all transitions belong
+  /// to the same acceptance sets.
+  ///
+  /// \param aut the automaton to check
+  ///
+  /// \param sm an scc_info object for the automaton if available (it
+  /// will be built otherwise).
+  SPOT_API bool
+  is_weak_automaton(const const_twa_graph_ptr& aut, scc_info* sm = nullptr);
+
   /// \brief Whether a minimized WDBA represents a safety property.
   ///
   /// A minimized WDBA (as returned by a successful run of