MDEV-452 Add full support for auto-initialized/updated timestamp and datetime

Generalized support for auto-updated and/or auto-initialized timestamp
and datetime columns. This patch is a reimplementation of MySQL's
"WL#5874: CURRENT_TIMESTAMP as DEFAULT for DATETIME columns". In order to
ease future merges, this implementation reused few function and variable
names from MySQL's patch, however the implementation is quite different.

TODO:
The only unresolved problem in this patch is the semantics of LOAD DATA for
TIMESTAMP and DATETIME columns in the cases when there are missing or NULL
columns. I couldn't fully comprehend the logic behind MySQL's behavior and
its relationship with their own documentation, so I left the results to be
more consistent with all other LOAD cases.

The problematic test cases can be seen by running the test file function_defaults,
and observing the test case differences. Those were left on purpose for discussion.

1 files changed, 19 insertions, 27 deletions

diff --git a/sql/sql_update.cc b/sql/sql_update.cc
index fb0951410a4..4f31da92107 100644
--- a/sql/sql_update.cc
+++ b/sql/sql_update.cc
@@ -342,19 +342,8 @@ int mysql_update(THD *thd,
     my_error(ER_NON_UPDATABLE_TABLE, MYF(0), table_list->alias, "UPDATE");
     DBUG_RETURN(1);
   }
-  if (table->timestamp_field)
-  {
-    // Don't set timestamp column if this is modified
-    if (bitmap_is_set(table->write_set,
-                      table->timestamp_field->field_index))
-      table->timestamp_field_type= TIMESTAMP_NO_AUTO_SET;
-    else
-    {
-      if (((uint) table->timestamp_field_type) & TIMESTAMP_AUTO_SET_ON_UPDATE)
-        bitmap_set_bit(table->write_set,
-                       table->timestamp_field->field_index);
-    }
-  }
+  if (table->default_field)
+    table->mark_default_fields_for_write();
 
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
   /* Check values */
@@ -389,7 +378,7 @@ int mysql_update(THD *thd,
     to compare records and detect data change.
   */
   if ((table->file->ha_table_flags() & HA_PARTIAL_COLUMN_READ) &&
-      (((uint) table->timestamp_field_type) & TIMESTAMP_AUTO_SET_ON_UPDATE))
+      table->default_field && table->has_default_function(true))
     bitmap_union(table->read_set, table->write_set);
   // Don't count on usage of 'only index' when calculating which key to use
   table->covering_keys.clear_all();
@@ -686,8 +675,7 @@ int mysql_update(THD *thd,
         continue;  /* repeat the read of the same row if it still exists */
 
       store_record(table,record[1]);
-      if (fill_record_n_invoke_before_triggers(thd, fields, values, 0,
-                                               table->triggers,
+      if (fill_record_n_invoke_before_triggers(thd, table, fields, values, 0,
                                                TRG_EVENT_UPDATE))
         break; /* purecov: inspected */
 
@@ -695,6 +683,11 @@ int mysql_update(THD *thd,
 
       if (!can_compare_record || compare_record(table))
       {
+        if (table->default_field && table->update_default_fields())
+        {
+          error= 1;
+          break;
+        }
         if ((res= table_list->view_check_option(thd, ignore)) !=
             VIEW_CHECK_OK)
         {
@@ -1241,11 +1234,6 @@ int mysql_multi_update_prepare(THD *thd)
   while ((tl= ti++))
   {
     TABLE *table= tl->table;
-    /* Only set timestamp column if this is not modified */
-    if (table->timestamp_field &&
-        bitmap_is_set(table->write_set,
-                      table->timestamp_field->field_index))
-      table->timestamp_field_type= TIMESTAMP_NO_AUTO_SET;
 
     /* if table will be updated then check that it is unique */
     if (table->map & tables_for_update)
@@ -1495,8 +1483,7 @@ int multi_update::prepare(List<Item> &not_used_values,
         to compare records and detect data change.
         */
       if ((table->file->ha_table_flags() & HA_PARTIAL_COLUMN_READ) &&
-          (((uint) table->timestamp_field_type) &
-           TIMESTAMP_AUTO_SET_ON_UPDATE))
+          table->default_field && table->has_default_function(true))
         bitmap_union(table->read_set, table->write_set);
     }
   }
@@ -1875,10 +1862,10 @@ int multi_update::send_data(List<Item> &not_used_values)
 
       table->status|= STATUS_UPDATED;
       store_record(table,record[1]);
-      if (fill_record_n_invoke_before_triggers(thd, *fields_for_table[offset],
+      if (fill_record_n_invoke_before_triggers(thd, table, *fields_for_table[offset],
                                                *values_for_table[offset], 0,
-                                               table->triggers,
-                                               TRG_EVENT_UPDATE))
+                                               TRG_EVENT_UPDATE) ||
+          (table->default_field && table->update_default_fields()))
 	DBUG_RETURN(1);
 
       /*
@@ -1979,7 +1966,7 @@ int multi_update::send_data(List<Item> &not_used_values)
       } while ((tbl= tbl_it++));
 
       /* Store regular updated fields in the row. */
-      fill_record(thd,
+      fill_record(thd, tmp_table,
                   tmp_table->field + 1 + unupdated_check_opt_tables.elements,
                   *values_for_table[offset], TRUE, FALSE);
 
@@ -2169,7 +2156,10 @@ int multi_update::do_updates()
       for (copy_field_ptr=copy_field;
 	   copy_field_ptr != copy_field_end;
 	   copy_field_ptr++)
+      {
 	(*copy_field_ptr->do_copy)(copy_field_ptr);
+        copy_field_ptr->to_field->set_explicit_default(NULL);
+      }
 
       if (table->triggers &&
           table->triggers->process_triggers(thd, TRG_EVENT_UPDATE,
@@ -2179,6 +2169,8 @@ int multi_update::do_updates()
       if (!can_compare_record || compare_record(table))
       {
         int error;
+        if (table->default_field && (error= table->update_default_fields()))
+          goto err2;
         if ((error= cur_table->view_check_option(thd, ignore)) !=
             VIEW_CHECK_OK)
         {