MDEV-15340 Wrong result HOUR(case_expression_with_time_and_datetime)

The problem was that Item_func_hybrid_field_type::get_date() did not
convert the result to the correct data type, so MYSQL_TIME::time_type
of the get_date() result could be not in sync with field_type().

Changes:
1. Adding two new classes Datetime and Date to store MYSQL_TIMESTAMP_DATETIME
   and MYSQL_TIMESTAMP_DATE values respectively
   (in addition to earlier added class Time, for MYSQL_TIMESTAMP_TIME values).
2. Adding Item_func_hybrid_field_type::time_op().
   It performs the operation using TIME representation,
   and always returns a MYSQL_TIME value with time_type=MYSQL_TIMESTAMP_TIME.
   Implementing time_op() for all affected children classes.
3. Fixing all implementations of date_op() to perform the operation
   using strictly DATETIME representation. Now they always return a MYSQL_TIME
   value with time_type=MYSQL_TIMESTAMP_{DATE|DATETIME},
   according to the result data type.
4. Removing assignment of ltime.time_type to mysql_timestamp_type()
   from all val_xxx_from_date_op(), because now date_op() makes sure
   to return a proper MYSQL_TIME value with a good time_type (and other member)
5. Adding Item_func_hybrid_field_type::val_xxx_from_time_op().
6. Overriding Type_handler_time_common::Item_func_hybrid_field_type_val_xxx()
   to call val_xxx_from_time_op() instead of val_xxx_from_date_op().
7. Modified Item_func::get_arg0_date() to return strictly a TIME value
   if TIME_TIME_ONLY is passed, or return strictly a DATETIME value otherwise.
   If args[0] returned a value of a different temporal type,
   (for example a TIME value when TIME_TIME_ONLY was not passed,
    or a DATETIME value when TIME_TIME_ONLY was passed), the conversion
   is automatically applied.
   Earlier, get_arg0_date() did not guarantee a result in
   accordance to TIME_TIME_ONLY flag.

sql/sql_type.cc

@@ -121,15 +121,41 @@ bool Type_handler_data::init()
 Type_handler_data *type_handler_data= NULL;
 
 
-void Time::make_from_item(Item *item)
+void Time::make_from_item(Item *item, sql_mode_t flags)
 {
-  if (item->get_time(this))
+  if (item->get_date(this, flags))
     time_type= MYSQL_TIMESTAMP_NONE;
   else
     valid_MYSQL_TIME_to_valid_value();
 }
 
 
+void Temporal_with_date::make_from_item(THD *thd, Item *item, sql_mode_t flags)
+{
+  flags&= ~TIME_TIME_ONLY;
+  /*
+    Some TIME type items return error when trying to do get_date()
+    without TIME_TIME_ONLY set (e.g. Item_field for Field_time).
+    In the SQL standard time->datetime conversion mode we add TIME_TIME_ONLY.
+    In the legacy time->datetime conversion mode we do not add TIME_TIME_ONLY
+    and leave it to get_date() to check date.
+  */
+  ulonglong time_flag= (item->field_type() == MYSQL_TYPE_TIME &&
+           !(thd->variables.old_behavior & OLD_MODE_ZERO_DATE_TIME_CAST)) ?
+           TIME_TIME_ONLY : 0;
+  if (item->get_date(this, flags | time_flag))
+    time_type= MYSQL_TIMESTAMP_NONE;
+  else if (time_type == MYSQL_TIMESTAMP_TIME)
+  {
+    MYSQL_TIME tmp;
+    if (time_to_datetime_with_warn(thd, this, &tmp, flags))
+      time_type= MYSQL_TIMESTAMP_NONE;
+    else
+      *(static_cast<MYSQL_TIME*>(this))= tmp;
+  }
+}
+
+
 void Type_std_attributes::set(const Field *field)
 {
   decimals= field->decimals();
@@ -3523,7 +3549,55 @@ Type_handler_temporal_result::Item_func_hybrid_field_type_get_date(
                                         MYSQL_TIME *ltime,
                                         ulonglong fuzzydate) const
 {
-  return item->get_date_from_date_op(ltime, fuzzydate);
+  return item->date_op(ltime, fuzzydate);
+}
+
+
+/***************************************************************************/
+
+String *
+Type_handler_time_common::Item_func_hybrid_field_type_val_str(
+                                    Item_func_hybrid_field_type *item,
+                                    String *str) const
+{
+  return item->val_str_from_time_op(str);
+}
+
+
+double
+Type_handler_time_common::Item_func_hybrid_field_type_val_real(
+                                    Item_func_hybrid_field_type *item)
+                                    const
+{
+  return item->val_real_from_time_op();
+}
+
+
+longlong
+Type_handler_time_common::Item_func_hybrid_field_type_val_int(
+                                    Item_func_hybrid_field_type *item)
+                                    const
+{
+  return item->val_int_from_time_op();
+}
+
+
+my_decimal *
+Type_handler_time_common::Item_func_hybrid_field_type_val_decimal(
+                                    Item_func_hybrid_field_type *item,
+                                    my_decimal *dec) const
+{
+  return item->val_decimal_from_time_op(dec);
+}
+
+
+bool
+Type_handler_time_common::Item_func_hybrid_field_type_get_date(
+                                    Item_func_hybrid_field_type *item,
+                                    MYSQL_TIME *ltime,
+                                    ulonglong fuzzydate) const
+{
+  return item->time_op(ltime);
 }