MDEV-23597 Assertion `marked_for_read()' failed while evaluating DEFAULT

The columns that are part of DEFAULT expression were not read-marked
in statements like UPDATE...SET b=DEFAULT.

The problem is `F(DEFAULT)` expression depends of the left-hand side of an
assignment. However, setup_fields accepts only right-hand side value.
Neither Item::fix_fields does.

Suchwise, b=DEFAULT(b) works fine, because Item_default_field has
information on what field it is default of:
    if (thd->mark_used_columns != MARK_COLUMNS_NONE)
      def_field->default_value->expr->update_used_tables();

in Item_default_value::fix_fields().

It is not reasonable to pass a left-hand side to Item:fix_fields, because
the case is rare, so the rewrite
  b= F(DEFAULT)  ->  b= F(DEFAULT(b))

is made instead.

Both UPDATE and multi-UPDATE are affected, however any form of INSERT
is not: it marks all the fields in DEFAULT expressions for read in
TABLE::mark_default_fields_for_write().

1 files changed, 12 insertions, 0 deletions

diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 3471297ac7d..9a66b27a454 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -7193,6 +7193,18 @@ int setup_wild(THD *thd, TABLE_LIST *tables, List<Item> &fields,
   DBUG_RETURN(0);
 }
 
+/** Transforms b= F(DEFAULT) -> b= F(DEFAULT(b)) */
+void setup_defaults(THD *thd, List<Item> &fields, List<Item> &values)
+{
+  List_iterator<Item> fit(fields);
+  List_iterator<Item> vit(values);
+
+  for (Item *value= vit++, *f_item= fit++; value; value= vit++, f_item= fit++)
+  {
+    value->walk(&Item::enchant_default_with_arg_processor, false, f_item);
+  }
+}
+
 /****************************************************************************
 ** Check that all given fields exists and fill struct with current data
 ****************************************************************************/