Bug#32803211: 8.0.22+ triggers fail in Item::mark_field_in_map

The problem was that when INSERT ... SET ... statement or UPDATE
statement was used in a trigger we have accepted reference to column
in the table on which trigger was defined (using NEW or OLD designator)
as an assigment target in its SET clause. This always led to
assertion failures in debug builds and sometimes server failures
in production builds.

The problem stemmed from two facts: 1) INSERT and UPDATE statement code
expects only references to their target table columns as assignment
targets of the SET clause 2) we didn't block usage of trigger
fields as target for such assignment, due to omission which has
happened during early days of implementation of triggers.

This patch solves the problem by rejecting trigger fields as
SET clause assignment targets in both INSERT and UPDATE.

This is an incompatible change which breaks rare user's triggers
which use this syntax (which might have been working somehow due
to luck). Such triggers produce an error during attempt to execute
them.

However, the new behavior is in line with both our documentation
and SQL standard, and supporting old non-standard and non-documented
behavor will require quite some efforts.
The fix for the problem is to reject trigger fields as SET clause
assignment targets in INSERT and UPDATE statements.

Reviewed by: Dmitry Lenev <Dmitry.Lenev@oracle.com>

Author: roylyseng

share/messages_to_clients.txt

@@ -9571,6 +9571,9 @@ ER_DA_ERROR_LOG_COMPONENT_FLUSH_FAILED
 ER_WARN_SQL_AFTER_MTS_GAPS_GAP_NOT_CALCULATED
   eng "The until clause SQL_AFTER_MTS_GAPS is being used for channel '%.192s' when GTID_MODE = ON and SOURCE_AUTO_POSITION=1 meaning the server did not compute internally what gaps may exist in the relay log transaction execution. To close any execution gaps use either the SQL_BEFORE_GTIDS or SQL_AFTER_GTIDS until clause."
 
+ER_INVALID_ASSIGNMENT_TARGET 42000
+  eng "Invalid target for assignment in INSERT or UPDATE statement '%.192s'."
+
 #
 #  End of 8.0 error messages (server-to-client).
 #  Do NOT add messages intended for the error log above!

sql/parse_tree_items.cc

@@ -410,9 +410,9 @@ bool PTI_simple_ident_q_2d::itemize(Parse_context *pc, Item **res) {
   sp_head *sp = lex->sphead;
 
   /*
-    FIXME This will work ok in simple_ident_nospvar case because
-    we can't meet simple_ident_nospvar in trigger now. But it
-    should be changed in future.
+    References with OLD and NEW designators can be used in expressions in
+    triggers. Semantic checks must ensure they are not used in invalid
+    contexts, such as assignment targets.
   */
   if (sp && sp->m_type == enum_sp_type::TRIGGER &&
       (!my_strcasecmp(system_charset_info, table, "NEW") ||

sql/sql_base.cc

@@ -9033,6 +9033,14 @@ bool setup_fields(THD *thd, ulong want_privilege, bool allow_sum_func,
         my_error(ER_NONUPDATEABLE_COLUMN, MYF(0), item->item_name.ptr());
         return true;
       }
+      if (item->type() == Item::TRIGGER_FIELD_ITEM) {
+        char buff[NAME_LEN * 2];
+        String str(buff, sizeof(buff), &my_charset_bin);
+        str.length(0);
+        item->print(thd, &str, QT_ORDINARY);
+        my_error(ER_INVALID_ASSIGNMENT_TARGET, MYF(0), str.c_ptr());
+        return true;
+      }
       TABLE_LIST *tr = field->table_ref;
       if ((want_privilege & UPDATE_ACL) && !tr->is_updatable()) {
         /*