Added decide-callback to user-propagator (#5978)

* Fixed registering expressions in push/pop

* Reused existing function

* Reverted reusing can_propagate

* Added decide-callback to user-propagator

* Refactoring

* Fixed index

src/api/api_solver.cpp

@@ -975,6 +975,14 @@ extern "C" {
         Z3_CATCH;
     }
 
+    void Z3_API Z3_solver_propagate_decide(Z3_context c, Z3_solver s, Z3_decide_eh decide_eh) {
+        Z3_TRY;
+        RESET_ERROR_CODE();
+        user_propagator::decide_eh_t c = (void(*)(void*, user_propagator::callback*, expr*&, unsigned&, lbool&))decide_eh;
+        to_solver_ref(s)->user_propagate_register_decide(c);
+        Z3_CATCH;
+    }
+
     Z3_func_decl Z3_API Z3_solver_propagate_declare(Z3_context c, Z3_symbol name, unsigned n, Z3_sort* domain, Z3_sort range) {
         Z3_TRY;
         LOG_Z3_solver_propagate_declare(c, name, n, domain, range);

src/api/c++/z3++.h

@@ -3943,11 +3943,13 @@ namespace z3 {
         typedef std::function<void(void)> final_eh_t;
         typedef std::function<void(expr const&, expr const&)> eq_eh_t;
         typedef std::function<void(expr const&)> created_eh_t;
+        typedef std::function<void(expr&, unsigned&, Z3_lbool&)> decide_eh_t;
 
         final_eh_t m_final_eh;
         eq_eh_t    m_eq_eh;
         fixed_eh_t m_fixed_eh;
         created_eh_t m_created_eh;
+        decide_eh_t m_decide_eh;
         solver*    s;
         context*   c;
         std::vector<z3::context*> subcontexts;
@@ -4009,8 +4011,15 @@ namespace z3 {
             expr e(p->ctx(), _e);
             p->m_created_eh(e);
         }
-
-
+        
+        static void decide_eh(void* _p, Z3_solver_callback cb, Z3_ast& _val, unsigned& bit, Z3_lbool& is_pos) {
+            user_propagator_base* p = static_cast<user_propagator_base*>(_p);
+            scoped_cb _cb(p, cb);
+            expr val(p->ctx(), _val);
+            p->m_decide_eh(val, bit, is_pos);
+            _val = val;
+        }
+        
     public:
         user_propagator_base(context& c) : s(nullptr), c(&c) {}
         
@@ -4119,6 +4128,22 @@ namespace z3 {
                 Z3_solver_propagate_created(ctx(), *s, created_eh);
             }
         }
+        
+        void register_decide(decide_eh_t& c) {
+            m_decide_eh = c;
+            if (s) {
+                Z3_solver_propagate_decide(ctx(), *s, decide_eh);
+            }
+        }
+
+        void register_decide() {
+            m_decide_eh = [this](expr& val, unsigned& bit, Z3_lbool& is_pos) {
+                decide(val, bit, is_pos);
+            };
+            if (s) {
+                Z3_solver_propagate_decide(ctx(), *s, decide_eh);
+            }
+        }
 
         virtual void fixed(expr const& /*id*/, expr const& /*e*/) { }
 
@@ -4127,6 +4152,8 @@ namespace z3 {
         virtual void final() { }
 
         virtual void created(expr const& /*e*/) {}
+        
+        virtual void decide(expr& /*val*/, unsigned& /*bit*/, Z3_lbool& /*is_pos*/) {}
 
         /**
            \brief tracks \c e by a unique identifier that is returned by the call.

src/api/z3_api.h

@@ -1444,6 +1444,7 @@ Z3_DECLARE_CLOSURE(Z3_fixed_eh,   void, (void* ctx, Z3_solver_callback cb, Z3_as
 Z3_DECLARE_CLOSURE(Z3_eq_eh,      void, (void* ctx, Z3_solver_callback cb, Z3_ast s, Z3_ast t));
 Z3_DECLARE_CLOSURE(Z3_final_eh,   void, (void* ctx, Z3_solver_callback cb));
 Z3_DECLARE_CLOSURE(Z3_created_eh, void, (void* ctx, Z3_solver_callback cb, Z3_ast t));
+Z3_DECLARE_CLOSURE(Z3_decide_eh,  void, (void* ctx, Z3_solver_callback cb, Z3_ast&, unsigned&, Z3_lbool&));
 
 
 /**
@@ -6758,6 +6759,14 @@ extern "C" {
     * The registered function appears at the top level and is created using \ref Z3_propagate_solver_declare.
     */
     void Z3_API Z3_solver_propagate_created(Z3_context c, Z3_solver s, Z3_created_eh created_eh);
+    
+    /**
+    * \brief register a callback when a the solver decides to split on a registered expression 
+    * The callback may set passed expression to another registered expression which will be selected instead.
+    * In case the expression is a bitvector the bit to split on is determined by the bit argument and the 
+    * truth-value to try first is given by is_pos
+    */
+    void Z3_API Z3_solver_propagate_decide(Z3_context c, Z3_solver s, Z3_decide_eh decide_eh);
 
     /**
         Create uninterpreted function declaration for the user propagator.