use only maxres if there is a lexicographic objective, fix #6697

- maxlex.enable heuristic does not work if it is chained among multiple objectives. Only maxres is set up to commit the proper constraints.

src/opt/maxsmt.cpp

@@ -178,14 +178,14 @@ namespace opt {
     maxsmt::maxsmt(maxsat_context& c, unsigned index):
         m(c.get_manager()), m_c(c), m_index(index), m_answer(m) {}
 
-    lbool maxsmt::operator()() {
+    lbool maxsmt::operator()(bool committed) {
         lbool is_sat = l_undef;
         m_msolver = nullptr;
         opt_params optp(m_params);
         symbol const& maxsat_engine = m_c.maxsat_engine();
         IF_VERBOSE(1, verbose_stream() << "(maxsmt)\n";);
         TRACE("opt_verbose", s().display(tout << "maxsmt\n") << "\n";);
-        if (optp.maxlex_enable() && is_maxlex(m_soft)) 
+        if (!committed && optp.maxlex_enable() && is_maxlex(m_soft)) 
             m_msolver = mk_maxlex(m_c, m_index, m_soft);            
         else if (m_soft.empty() || maxsat_engine == symbol("maxres") || maxsat_engine == symbol::null)             
             m_msolver = mk_maxres(m_c, m_index, m_soft);            
@@ -401,7 +401,7 @@ namespace opt {
         for (auto const& p : soft) {
             maxsmt.add(p.first, p.second);
         }
-        lbool r = maxsmt();
+        lbool r = maxsmt(true);
         if (r == l_true) {
             svector<symbol> labels;
             maxsmt.get_model(m_model, labels);

src/opt/maxsmt.h

@@ -137,7 +137,7 @@ namespace opt {
         params_ref       m_params;
     public:
         maxsmt(maxsat_context& c, unsigned id);
-        lbool operator()();
+        lbool operator()(bool committed);
         void updt_params(params_ref& p);
         void add(expr* f, rational const& w); 
         unsigned size() const { return m_soft.size(); }

src/opt/opt_context.cpp

@@ -453,8 +453,8 @@ namespace opt {
     lbool context::execute_maxsat(symbol const& id, bool committed, bool scoped) {
         model_ref tmp;
         maxsmt& ms = *m_maxsmts.find(id);
-        if (scoped) get_solver().push();            
-        lbool result = ms();
+        if (scoped) get_solver().push();         
+        lbool result = ms(committed);
         if (result != l_false && (ms.get_model(tmp, m_labels), tmp.get())) {
             ms.get_model(m_model, m_labels);
         }