MDEV-20403 Assertion 0' or Assertion btr_validate_index(index, 0)' …

…failed in row_upd_sec_index_entry or error code 126: Index is corrupted upon UPDATE with TIMESTAMP..ON UPDATE

remove a special treatment of a bare DEFAULT keyword that made it
behave inconsistently and differently from DEFAULT(column).
Now all forms of the explicit assignment of a default column value
behave identically, and all count as an explicitly assigned value
(for the purpose of ON UPDATE NOW).

followup for c7c481f

mysql-test/r/default.result

@@ -3372,7 +3372,7 @@ insert into t1 values (b, 5, '5 the value of the DEFAULT(a), that is b');
 select * from t1 order by t;
 a	b	t
 5	5	1 column is omitted
-5	5	2 column gets DEFAULT, keyword
+4	5	2 column gets DEFAULT, keyword
 4	5	3 column gets DEFAULT(a), expression
 4	5	4 also expression DEFAULT(0)+0
 4	5	5 the value of the DEFAULT(a), that is b

mysql-test/r/function_defaults.result

@@ -3116,3 +3116,32 @@ select if(@new = j, 'correct', 'wrong') from t1;
 if(@new = j, 'correct', 'wrong')
 correct
 drop table t1;
+create table t1 (a int, b varchar(20) default 'foo');
+insert t1 values (1,'bla'),(2, 'bar');
+select * from t1;
+a	b
+1	bla
+2	bar
+update t1 set b=default where a=1;
+select * from t1;
+a	b
+1	foo
+2	bar
+drop table t1;
+create table t1 (
+a int,
+b timestamp default '2010-10-10 10:10:10' on update now(),
+c varchar(100) default 'x');
+insert t1 (a) values (1),(2);
+select * from t1;
+a	b	c
+1	2010-10-10 10:10:10	x
+2	2010-10-10 10:10:10	x
+set timestamp=unix_timestamp('2011-11-11 11-11-11');
+update t1 set b=default, c=default(b) where a=1;
+select * from t1;
+a	b	c
+1	2010-10-10 10:10:10	2010-10-10 10:10:10
+2	2010-10-10 10:10:10	x
+drop table t1;
+set timestamp=default;

mysql-test/t/function_defaults.test

@@ -24,14 +24,14 @@ source 'include/function_defaults.inc';
 # MDEV-20403 Assertion `0' or Assertion `btr_validate_index(index, 0)' failed in row_upd_sec_index_entry or error code 126: Index is corrupted upon UPDATE with TIMESTAMP..ON UPDATE
 #
 
-# ON UPDATE DEFAULT NOW and indexed virtual columns
+# ON UPDATE NOW and indexed virtual columns
 create table t1 (t timestamp, i int, v timestamp as (t) virtual, key(v));
 insert t1 (t,i) values ('2006-03-01 23:59:59',1);
 update t1 set i = 2;
 check table t1;
 drop table t1;
 
-# ON UPDATE DEFAULT NOW and triggers
+# ON UPDATE NOW and triggers
 create table t1 (t timestamp, i int);
 create trigger tr1 before update on t1 for each row set @new:=new.t;
 insert t1 (t,i) values ('2006-03-01 23:59:59', 1);
@@ -46,3 +46,24 @@ insert t1 (i) values (1);
 update t1, t1 as t2 set t1.i = 2;
 select if(@new = j, 'correct', 'wrong') from t1;
 drop table t1;
+
+# SET xxx=DEFAULT
+create table t1 (a int, b varchar(20) default 'foo');
+insert t1 values (1,'bla'),(2, 'bar');
+select * from t1;
+update t1 set b=default where a=1;
+select * from t1;
+drop table t1;
+
+# ON UPDATE NOW and SET xxx=DEFAULT
+create table t1 (
+  a int,
+  b timestamp default '2010-10-10 10:10:10' on update now(),
+  c varchar(100) default 'x');
+insert t1 (a) values (1),(2);
+select * from t1;
+set timestamp=unix_timestamp('2011-11-11 11-11-11');
+update t1 set b=default, c=default(b) where a=1;
+select * from t1;
+drop table t1;
+set timestamp=default;

sql/field.cc

@@ -11106,33 +11106,6 @@ key_map Field::get_possible_keys()
 }
 
 
-/**
-  Mark the field as having an explicit default value.
-
-  @param value  if available, the value that the field is being set to
-
-  @note
-    Fields that have an explicit default value should not be updated
-    automatically via the DEFAULT or ON UPDATE functions. The functions
-    that deal with data change functionality (INSERT/UPDATE/LOAD),
-    determine if there is an explicit value for each field before performing
-    the data change, and call this method to mark the field.
-
-    If the 'value' parameter is NULL, then the field is marked unconditionally
-    as having an explicit value. If 'value' is not NULL, then it can be further
-    analyzed to check if it really should count as a value.
-*/
-
-bool Field::set_explicit_default(Item *value)
-{
-  if (value->type() == Item::DEFAULT_VALUE_ITEM &&
-      !((Item_default_value*)value)->arg)
-    return false;
-  set_has_explicit_value();
-  return true;
-}
-
-
 bool Field::validate_value_in_record_with_warn(THD *thd, const uchar *record)
 {
   my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->read_set);

sql/field.h

@@ -990,7 +990,6 @@ class Field: public Value_source
   {
     return bitmap_is_set(&table->has_value_set, field_index);
   }
-  bool set_explicit_default(Item *value);
 
   virtual bool binary() const { return 1; }
   virtual bool zero_pack() const { return 1; }

sql/item.cc

@@ -9010,8 +9010,6 @@ int Item_default_value::save_in_field(Field *field_arg, bool no_conversions)
     return Item_field::save_in_field(field_arg, no_conversions);
   }
 
-  if (field_arg->default_value && field_arg->default_value->flags)
-    return 0; // defaut fields will be set later, no need to do it twice
   return field_arg->save_in_field_default_value(context->error_processor ==
                                                 &view_error_processor);
 }
@@ -9263,7 +9261,7 @@ bool Item_trigger_field::set_value(THD *thd, sp_rcontext * /*ctx*/, Item **it)
   int err_code= item->save_in_field(field, 0);
 
   field->table->copy_blobs= copy_blobs_saved;
-  field->set_explicit_default(item);
+  field->set_has_explicit_value();
 
   return err_code < 0;
 }

sql/sql_base.cc

@@ -8068,7 +8068,7 @@ fill_record(THD *thd, TABLE *table_arg, List<Item> &fields, List<Item> &values,
       my_message(ER_UNKNOWN_ERROR, ER_THD(thd, ER_UNKNOWN_ERROR), MYF(0));
       goto err;
     }
-    rfield->set_explicit_default(value);
+    rfield->set_has_explicit_value();
   }
 
   if (update)
@@ -8265,7 +8265,6 @@ fill_record(THD *thd, TABLE *table, Field **ptr, List<Item> &values,
 {
   List_iterator_fast<Item> v(values);
   List<TABLE> tbl_list;
-  bool all_fields_have_values= true;
   Item *value;
   Field *field;
   bool abort_on_warning_saved= thd->abort_on_warning;
@@ -8318,11 +8317,8 @@ fill_record(THD *thd, TABLE *table, Field **ptr, List<Item> &values,
     else
       if (value->save_in_field(field, 0) < 0)
         goto err;
-    all_fields_have_values &= field->set_explicit_default(value);
+    field->set_has_explicit_value();
   }
-  if (!all_fields_have_values && table->default_field &&
-      table->update_default_fields(ignore_errors))
-    goto err;
   /* Update virtual fields */
   thd->abort_on_warning= FALSE;
   if (table->vfield &&