MDEV-14494 Move set_param_xxx() in sql_prepare.cc to methods in Item_…

…param and Type_handler

- sql_prepare.cc: Moving functions set_param_xxx() as
  methods to Item_param

- Replacing a pointer to a function Item_param::set_param_func
  to Type_handler based implementation:
  Item_param::value now derives from Type_handler_hybrid_field_type.
  Adding new virtual methods Type_handler::Item_param_setup_conversion()
  and Type_handler::Item_param_set_param_func()

- Moving declaration of some Item_param members  from "public:" to "private:"
  (CONVERSION_INFO, value, decimal_value)

- Adding a new method Item_param::set_limit_clause_param(),
  to share duplicate code, as well as to encapsulate
  Item_param::value.

- Adding Item_param::setup_conversion_string() and
  Item_param::setup_conversion_blob() to share
  the code for binding from a client value
  (mysql_stmt_bind_param), and for binding from
  an expression (Item).

- Removing two different functions set_param_str_or_null()
  and set_param_str(). Adding a common method Item_param::set_param_str().
  Item_param::m_empty_string_is_null, used by Item_param::set_param_str().

- Removing the call for setup_one_conversion_function() from
  insert_params_from_actual_params_with_log(). It's not needed,
  because the call for ps_param->save_in_param() makes sure
  to initialized all data type dependent members properly,
  by calling setup_conversion_string() from
  Type_handler_string_result::Item_param_set_from_value()
  and by calling setup_conversion_blob() from
  Type_handler_blob_common::Item_param_set_from_value()

- Cleanup: removing multiplication to MY_CHARSET_BIN_MB_MAXLEN
  in a few places. It's 1 anyway, and will never change.

sql/item.cc

@@ -3708,20 +3708,6 @@ Item *Item_null::clone_item(THD *thd)
 
 /*********************** Item_param related ******************************/
 
-/** 
-  Default function of Item_param::set_param_func, so in case
-  of malformed packet the server won't SIGSEGV.
-*/
-
-static void
-default_set_param_func(Item_param *param,
-                       uchar **pos __attribute__((unused)),
-                       ulong len __attribute__((unused)))
-{
-  param->set_null();
-}
-
-
 Item_param::Item_param(THD *thd, const LEX_CSTRING *name_arg,
                        uint pos_in_query_arg, uint len_in_query_arg):
   Item_basic_value(thd),
@@ -3739,8 +3725,8 @@ Item_param::Item_param(THD *thd, const LEX_CSTRING *name_arg,
   state(NO_VALUE),
   /* Don't pretend to be a literal unless value for this item is set. */
   item_type(PARAM_ITEM),
+  m_empty_string_is_null(false),
   indicator(STMT_INDICATOR_NONE),
-  set_param_func(default_set_param_func),
   m_out_param_info(NULL),
   /*
     Set m_is_settable_routine_parameter to "true" by default.
@@ -4025,9 +4011,8 @@ bool Item_param::set_from_item(THD *thd, Item *item)
     else
     {
       unsigned_flag= item->unsigned_flag;
-      set_int(val, MY_INT64_NUM_DECIMAL_DIGITS);
       set_handler_by_result_type(item->result_type());
-      DBUG_RETURN(!unsigned_flag && value.integer < 0 ? 1 : 0);
+      DBUG_RETURN(set_limit_clause_param(val));
     }
   }
   struct st_value tmp;
@@ -4535,7 +4520,6 @@ Item_param::set_param_type_and_swap_value(Item_param *src)
 {
   Type_std_attributes::set(src);
   set_handler(src->type_handler());
-  set_param_func= src->set_param_func;
   item_type= src->item_type;
 
   maybe_null= src->maybe_null;
@@ -4544,6 +4528,7 @@ Item_param::set_param_type_and_swap_value(Item_param *src)
   fixed= src->fixed;
   value= src->value;
 
+  value.set_handler(src->value.type_handler());
   decimal_value.swap(src->decimal_value);
   str_value.swap(src->str_value);
   str_value_ptr.swap(src->str_value_ptr);

sql/item.h

@@ -3128,7 +3128,6 @@ class Item_param :public Item_basic_value,
 
   void fix_temporal(uint32 max_length_arg, uint decimals_arg);
 
-public:
   struct CONVERSION_INFO
   {
     /*
@@ -3170,12 +3169,6 @@ class Item_param :public Item_basic_value,
     }
   };
 
-  /*
-    Used for bulk protocol only.
-  */
-  enum enum_indicator_type indicator;
-
-private:
   /*
     A buffer for string and long data values. Historically all allocated
     values returned from val_str() were treated as eligible to
@@ -3188,15 +3181,30 @@ class Item_param :public Item_basic_value,
   */
   String str_value_ptr;
 
-public:
-  my_decimal decimal_value;
-  union
+  bool m_empty_string_is_null;
+
+  class PValue: public Type_handler_hybrid_field_type
   {
-    longlong integer;
-    double   real;
-    CONVERSION_INFO cs_info;
-    MYSQL_TIME     time;
-  } value;
+  public:
+    PValue(): Type_handler_hybrid_field_type(&type_handler_null) {}
+    union
+    {
+      longlong integer;
+      double   real;
+      CONVERSION_INFO cs_info;
+      MYSQL_TIME     time;
+    };
+  };
+
+  PValue value;
+
+  my_decimal decimal_value;
+
+public:
+  /*
+    Used for bulk protocol only.
+  */
+  enum enum_indicator_type indicator;
 
   const Type_handler *type_handler() const
   { return Type_handler_hybrid_field_type::type_handler(); }
@@ -3237,14 +3245,39 @@ class Item_param :public Item_basic_value,
   void set_time(const MYSQL_TIME *tm, uint32 max_length_arg, uint decimals_arg);
   bool set_from_item(THD *thd, Item *item);
   void reset();
+
+  void set_param_tiny(uchar **pos, ulong len);
+  void set_param_short(uchar **pos, ulong len);
+  void set_param_int32(uchar **pos, ulong len);
+  void set_param_int64(uchar **pos, ulong len);
+  void set_param_float(uchar **pos, ulong len);
+  void set_param_double(uchar **pos, ulong len);
+  void set_param_decimal(uchar **pos, ulong len);
+  void set_param_time(uchar **pos, ulong len);
+  void set_param_datetime(uchar **pos, ulong len);
+  void set_param_date(uchar **pos, ulong len);
+  void set_param_str(uchar **pos, ulong len);
+
+  void setup_conversion(THD *thd, uchar param_type);
+  void setup_conversion_blob(THD *thd);
+  void setup_conversion_string(THD *thd, CHARSET_INFO *fromcs);
+
   /*
     Assign placeholder value from bind data.
     Note, that 'len' has different semantics in embedded library (as we
     don't need to check that packet is not broken there). See
     sql_prepare.cc for details.
   */
-  void (*set_param_func)(Item_param *param, uchar **pos, ulong len);
+  void set_param_func(uchar **pos, ulong len)
+  {
+    value.type_handler()->Item_param_set_param_func(this, pos, len);
+  }
 
+  bool set_limit_clause_param(longlong nr)
+  {
+    set_int(nr, MY_INT64_NUM_DECIMAL_DIGITS);
+    return !unsigned_flag && value.integer < 0;
+  }
   const String *query_val_str(THD *thd, String *str) const;
 
   bool convert_str_value(THD *thd);