A cleanup for MDEV-15340 + fix MDEV-15363 Wrong result for CAST(LAST_DAY(TIME'00:00:00') AS TIME)

The change N7 in MDEV-15340 (see the commit message) introduced
a regression in how CAST(AS TIME), HOUR(), TIME_TO_SEC() treat datetimes
'0000-00-DD mm:hh:ss' (i.e. with zero YYYYMM part and a non-zero day).
These functions historically do not mix days to hours on datetime-to-time
conversion. Implementations of the underlying methods used get_arg0_time()
to fetch MYSQL_TIME. After MDEV-15340, get_arg0_time() went through the
Time() constructor, which always adds '0000-00-DD' to hours automatically
(as in all other places in the code we do mix days to hours).

Changes:
1. Extending Time() to make it possible to choose a desired way of treating
   '0000-00-DD' (ignore or mix to hours) on datetime-to-time conversion.
   Adding a helper class Time::Options for this, which now describes two aspects
   of Time() creation:
   1. Flags for get_date()
   2. Days/hours mixing behavior.

2. Removing Item_func::get_arg0_time(). Using Time() directly
   in all affected classes. Forcing Time() to ignore (rather than mix)
   '0000-00-DD' in these affected classes by passing a suitable Options value.

3. Adding Time::to_seconds(), to reuse the code between
   Item_func_time_to_sec::decimal_op() and Item_func_time_to_sec::int_op().

4. Item_func::get_arg0_date() now returns only a datetime value,
   with automatic time-to-datetime conversion if needed. An assert was
   added to catch attempts to pass TIME_TIME_ONLY to get_arg0_date().
   All callers were checked not to pass TIME_TIME_ONLY, this revealed
   a bug MDEV-15363.

5. Changing Item_func_last_day::get_date() to remove the TIME_TIME_ONLY flag
   before calling get_arg0_date(). This fixes MDEV-15363.

1 files changed, 1 insertions, 9 deletions

diff --git a/sql/item_func.h b/sql/item_func.h
index 063a80de737..7d7cd61f474 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -160,18 +160,10 @@ public:
   void print_args(String *str, uint from, enum_query_type query_type);
   inline bool get_arg0_date(MYSQL_TIME *ltime, ulonglong fuzzy_date)
   {
-    return fuzzy_date & TIME_TIME_ONLY ? get_arg0_time(ltime) :
-                                         get_arg0_datetime(ltime, fuzzy_date);
-  }
-  inline bool get_arg0_datetime(MYSQL_TIME *ltime, ulonglong fuzzy_date)
-  {
+    DBUG_ASSERT(!(fuzzy_date & TIME_TIME_ONLY));
     Datetime dt(current_thd, args[0], fuzzy_date);
     return (null_value= dt.copy_to_mysql_time(ltime));
   }
-  inline bool get_arg0_time(MYSQL_TIME *ltime)
-  {
-    return (null_value= Time(args[0]).copy_to_mysql_time(ltime));
-  }
   bool is_null() { 
     update_null_value();
     return null_value;