MDEV-26095 Infinite recursion when processing embedded recursive CTE

           with missing RECURSIVE

If a table reference r used inthe specification of a CTE whose definition
is contained in the WITH clause where RECURSIVE is omitted then this table
reference cannot be considered as a recursive table reference even if it is
used in the query that specifies CTE whose name is r. It can be considered
only as a reference to an embedding CTE or to a temporary table or to
a base table/view. If there is no such object with name r then an error
message must be reported.
This patch fixes the code that actually in some cases resolved r as a
reference to the CTE whose specification contained r if its name was r
in spite of the fact that r was not considered as a recursive CTE.
This happened in the cases when the definition of r was used in the
specification of another CTE. Such wrong name resolution for r led to an
infinite recursive invocations of the parser that ultimately crashed the
server.
This bug is a result of the fix for mdev-13780 that was not quite correct.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/r/cte_nonrecursive.result

@@ -2019,4 +2019,29 @@ drop procedure sp1;
 drop procedure sp2;
 drop procedure sp3;
 drop table t1;
+#
+# MDEV-26095: missing RECURSIVE for the recursive definition of CTE
+#             embedded into another CTE definition
+#
+create table t1 (a int);
+insert into t1 values (5), (7);
+with cte_e as (
+with recursive cte_r as (
+select a from t1 union select a+1 as a from cte_r r where a < 10
+) select * from cte_r
+) select * from cte_e;
+a
+5
+7
+6
+8
+9
+10
+with cte_e as (
+with cte_r as (
+select a from t1 union select a+1 as a from cte_r r where a < 10
+) select * from cte_r
+) select * from cte_e;
+ERROR 42S02: Table 'test.cte_r' doesn't exist
+drop table t1;
 # End of 10.2 tests

mysql-test/t/cte_nonrecursive.test

@@ -1492,4 +1492,27 @@ drop procedure sp3;
 
 drop table t1;
 
+--echo #
+--echo # MDEV-26095: missing RECURSIVE for the recursive definition of CTE
+--echo #             embedded into another CTE definition
+--echo #
+
+create table t1 (a int);
+insert into t1 values (5), (7);
+
+with cte_e as (
+  with recursive cte_r as (
+    select a from t1 union select a+1 as a from cte_r r where a < 10
+  ) select * from cte_r
+) select * from cte_e;
+
+--ERROR ER_NO_SUCH_TABLE
+with cte_e as (
+  with cte_r as (
+    select a from t1 union select a+1 as a from cte_r r where a < 10
+  ) select * from cte_r
+) select * from cte_e;
+
+drop table t1;
+
 --echo # End of 10.2 tests

sql/sql_cte.cc

@@ -1256,6 +1256,7 @@ bool With_element::is_anchor(st_select_lex *sel)
 With_element *st_select_lex::find_table_def_in_with_clauses(TABLE_LIST *table)
 {
   With_element *found= NULL;
+  With_clause *containing_with_clause= NULL;
   st_select_lex_unit *master_unit;
   st_select_lex *outer_sl;
   for (st_select_lex *sl= this; sl; sl= outer_sl)
@@ -1268,6 +1269,7 @@ With_element *st_select_lex::find_table_def_in_with_clauses(TABLE_LIST *table)
     */
     With_clause *attached_with_clause= sl->get_with_clause();
     if (attached_with_clause &&
+        attached_with_clause != containing_with_clause &&
         (found= attached_with_clause->find_table_def(table, NULL)))
       break;
     master_unit= sl->master_unit();
@@ -1275,7 +1277,7 @@ With_element *st_select_lex::find_table_def_in_with_clauses(TABLE_LIST *table)
     With_element *with_elem= sl->get_with_element();
     if (with_elem)
     {
-      With_clause *containing_with_clause= with_elem->get_owner();
+      containing_with_clause= with_elem->get_owner();
       With_element *barrier= containing_with_clause->with_recursive ?
                                NULL : with_elem;
       if ((found= containing_with_clause->find_table_def(table, barrier)))