MDEV-23221: A subquery causes crash

* Fix the crash: IN-to-EXISTS rewrite causes an error (and so
  JOIN::optimize() fails with an error, too), don't call
  update_used_tables(). Terminate the query execution instead.

* Fix the cause of the error in the IN-to-EXISTS rewrite: don't do
  the rewrite if doing it will cause an error of this kind:
  This version of MariaDB doesn't yet support 'SUBQUERY in ROW in left
  expression of IN/ALL/ANY'

* Fix another issue exposed by this testcase:
  JOIN::setup_subquery_caches() may be invoked before any select has
  saved its query plan, and will crash because none of the SELECTs
  has called create_explain_query_if_not_exists() to create the Explain
  Data Structure for this SELECT.

TODO: When merging this to 10.2, remove the poorly-placed call to
create_explain_query_if_not_exists made by fix for M_D_E_V-16153

mysql-test/r/subselect_exists2in.result

@@ -972,4 +972,74 @@ id
 DROP PROCEDURE p1;
 DROP TABLE t1;
 # End of 10.0 tests
+#
+# MDEV-23221: A subquery causes crash
+#
+create table t1 (
+location_code varchar(10),
+country_id varchar(10)
+);
+insert into t1 values ('HKG', 'HK');
+insert into t1 values ('NYC', 'US');
+insert into t1 values ('LAX', 'US');
+create table t2 (
+container_id varchar(10),
+cntr_activity_type varchar(10),
+cntr_dest varchar(10)
+);
+insert into t2 values ('AAAA1111', 'VSL', 'NYC');
+insert into t2 values ('AAAA1111', 'CUV', 'NYC');
+insert into t2 values ('BBBB2222', 'VSL', 'LAX');
+insert into t2 values ('BBBB2222', 'XYZ', 'LAX');
+# Must not crash or return an error:
+select
+(select country_id from t1 where location_code = cl1.cntr_dest) as dest_cntry,
+(select
+max(container_id)
+from t2 as cl2
+where
+cl2.container_id = cl1.container_id and
+cl2.cntr_activity_type = 'CUV' and
+exists (select location_code
+from t1
+where
+location_code = cl2.cntr_dest and
+country_id = dest_cntry)
+) as CUV
+from
+t2 cl1;
+dest_cntry	CUV
+US	AAAA1111
+US	AAAA1111
+US	NULL
+US	NULL
+prepare s from "select
+(select country_id from t1 where location_code = cl1.cntr_dest) as dest_cntry,
+(select
+max(container_id)
+from t2 as cl2
+where
+cl2.container_id = cl1.container_id and
+cl2.cntr_activity_type = 'CUV' and
+exists (select location_code
+from t1
+where
+location_code = cl2.cntr_dest and
+country_id = dest_cntry)
+) as CUV
+from
+t2 cl1";
+execute s;
+dest_cntry	CUV
+US	AAAA1111
+US	AAAA1111
+US	NULL
+US	NULL
+execute s;
+dest_cntry	CUV
+US	AAAA1111
+US	AAAA1111
+US	NULL
+US	NULL
+drop table t1,t2;
 set optimizer_switch=default;

mysql-test/t/subselect_exists2in.test

@@ -828,5 +828,53 @@ DROP TABLE t1;
 
 --echo # End of 10.0 tests
 
+--echo #
+--echo # MDEV-23221: A subquery causes crash
+--echo #
+create table t1 (
+location_code varchar(10),
+country_id varchar(10)
+);
+insert into t1 values ('HKG', 'HK');
+insert into t1 values ('NYC', 'US');
+insert into t1 values ('LAX', 'US');
+
+create table t2 (
+container_id varchar(10),
+cntr_activity_type varchar(10),
+cntr_dest varchar(10)
+);
+insert into t2 values ('AAAA1111', 'VSL', 'NYC');
+insert into t2 values ('AAAA1111', 'CUV', 'NYC');
+insert into t2 values ('BBBB2222', 'VSL', 'LAX');
+insert into t2 values ('BBBB2222', 'XYZ', 'LAX');
+
+let $query=
+select
+  (select country_id from t1 where location_code = cl1.cntr_dest) as dest_cntry,
+  (select
+     max(container_id)
+   from t2 as cl2
+   where
+    cl2.container_id = cl1.container_id and
+    cl2.cntr_activity_type = 'CUV' and
+    exists (select location_code
+            from t1
+            where
+               location_code = cl2.cntr_dest and
+               country_id = dest_cntry)
+   ) as CUV
+from
+  t2 cl1;
+
+--echo # Must not crash or return an error:
+eval $query;
+
+eval prepare s from "$query";
+execute s;
+execute s;
+
+drop table t1,t2;
+
 #restore defaults
 set optimizer_switch=default;

sql/item_subselect.cc

@@ -2727,13 +2727,16 @@ bool Item_exists_subselect::select_prepare_to_be_in()
   Check if 'func' is an equality in form "inner_table.column = outer_expr"
 
   @param func              Expression to check
+  @param allow_subselect   If true, the outer_expr part can have a subquery
+                           If false, it cannot.
   @param local_field  OUT  Return "inner_table.column" here
   @param outer_expr   OUT  Return outer_expr here
 
   @return true - 'func' is an Equality.
 */
 
 static bool check_equality_for_exist2in(Item_func *func,
+                                        bool allow_subselect,
                                         Item_ident **local_field,
                                         Item **outer_exp)
 {
@@ -2744,7 +2747,8 @@ static bool check_equality_for_exist2in(Item_func *func,
   args= func->arguments();
   if (args[0]->real_type() == Item::FIELD_ITEM &&
       args[0]->all_used_tables() != OUTER_REF_TABLE_BIT &&
-      args[1]->all_used_tables() == OUTER_REF_TABLE_BIT)
+      args[1]->all_used_tables() == OUTER_REF_TABLE_BIT &&
+      (allow_subselect || !args[1]->has_subquery()))
   {
     /* It is Item_field or Item_direct_view_ref) */
     DBUG_ASSERT(args[0]->type() == Item::FIELD_ITEM ||
@@ -2755,7 +2759,8 @@ static bool check_equality_for_exist2in(Item_func *func,
   }
   else if (args[1]->real_type() == Item::FIELD_ITEM &&
            args[1]->all_used_tables() != OUTER_REF_TABLE_BIT &&
-           args[0]->all_used_tables() == OUTER_REF_TABLE_BIT)
+           args[0]->all_used_tables() == OUTER_REF_TABLE_BIT &&
+           (allow_subselect || !args[0]->has_subquery()))
   {
     /* It is Item_field or Item_direct_view_ref) */
     DBUG_ASSERT(args[1]->type() == Item::FIELD_ITEM ||
@@ -2784,6 +2789,13 @@ typedef struct st_eq_field_outer
 
     outer1=inner_tbl1.col1 AND ... AND outer2=inner_tbl1.col2 AND remainder_cond
 
+    if there is just one outer_expr=inner_expr pair, then outer_expr can have a
+    subselect in it.  If there are many such pairs, then none of outer_expr can
+    have a subselect in it. If we allow this, the query will fail with an error:
+
+      This version of MariaDB doesn't yet support 'SUBQUERY in ROW in left
+      expression of IN/ALL/ANY'
+
   @param  conds    Condition to be checked
   @parm   result   Array to collect EQ_FIELD_OUTER elements describing
                    inner-vs-outer equalities the function has found.
@@ -2801,14 +2813,17 @@ static bool find_inner_outer_equalities(Item **conds,
   {
     List_iterator<Item> li(*((Item_cond*)*conds)->argument_list());
     Item *item;
+    bool allow_subselect= true;
     while ((item= li++))
     {
       if (item->type() == Item::FUNC_ITEM &&
           check_equality_for_exist2in((Item_func *)item,
+                                      allow_subselect,
                                       &element.local_field,
                                       &element.outer_exp))
       {
         found= TRUE;
+        allow_subselect= false;
         element.eq_ref= li.ref();
         if (result.append(element))
           goto alloc_err;
@@ -2817,6 +2832,7 @@ static bool find_inner_outer_equalities(Item **conds,
   }
   else if ((*conds)->type() == Item::FUNC_ITEM &&
            check_equality_for_exist2in((Item_func *)*conds,
+                                       true,
                                        &element.local_field,
                                        &element.outer_exp))
   {

sql/sql_lex.cc

@@ -3802,7 +3802,8 @@ bool st_select_lex::optimize_unflattened_subqueries(bool const_only)
           sl->options|= SELECT_DESCRIBE;
           inner_join->select_options|= SELECT_DESCRIBE;
         }
-        res= inner_join->optimize();
+        if ((res= inner_join->optimize()))
+          return TRUE;
         if (!inner_join->cleaned)
           sl->update_used_tables();
         sl->update_correlated_cache();

sql/sql_select.cc

@@ -1055,11 +1055,11 @@ int JOIN::optimize()
   if (optimization_state != JOIN::NOT_OPTIMIZED)
     return FALSE;
   optimization_state= JOIN::OPTIMIZATION_IN_PROGRESS;
+  create_explain_query_if_not_exists(thd->lex, thd->mem_root);
 
   int res= optimize_inner();
   if (!res && have_query_plan != QEP_DELETED)
   {
-    create_explain_query_if_not_exists(thd->lex, thd->mem_root);
     have_query_plan= QEP_AVAILABLE;
     save_explain_data(thd->lex->explain, false /* can overwrite */,
                       need_tmp,