MDEV-28958 Crash when checking whether condition can be pushed into view

Do not set any flags in the items for constant subformulas TRUE/FALSE when
checking pushability of a formula into a view. Occurrences of these
subformulas can be ignored when checking pushability of the formula.
At the same time the items used for these constants became immutable
starting from version 10.7.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/main/derived_cond_pushdown.result

@@ -20697,3 +20697,20 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 drop view v1;
 drop table t1;
 # End of 10.4 tests
+#
+# MDEV-28958: condition pushable into view after simplification
+#             contains constant TRUE/FALSE as subformula
+#
+create table t1 (c1 int);
+insert into t1 values (3), (7), (1), (3), (1), (3);
+create table t2 (c2 int);
+insert into t2 values (3), (5), (7), (3);
+create view v1 as select * from t1 group by c1;
+create view v2 as select c1 as a, c2 as b from v1,t2 where c1=c2;
+select * from v2 group by a,b having a=b or b > a+10;
+a	b
+3	3
+7	7
+drop view v1,v2;
+drop table t1,t2;
+# End of 10.7 tests

mysql-test/main/derived_cond_pushdown.test

@@ -3944,3 +3944,24 @@ drop view v1;
 drop table t1;
 
 --echo # End of 10.4 tests
+
+--echo #
+--echo # MDEV-28958: condition pushable into view after simplification
+--echo #             contains constant TRUE/FALSE as subformula
+--echo #
+
+create table t1 (c1 int);
+insert into t1 values (3), (7), (1), (3), (1), (3);
+
+create table t2 (c2 int);
+insert into t2 values (3), (5), (7), (3);
+
+create view v1 as select * from t1 group by c1;
+create view v2 as select c1 as a, c2 as b from v1,t2 where c1=c2;
+
+select * from v2 group by a,b having a=b or b > a+10;
+
+drop view v1,v2;
+drop table t1,t2;
+
+--echo # End of 10.7 tests

sql/item.h

@@ -2687,18 +2687,27 @@ class Item :public Value_source,
   void register_in(THD *thd);	 
   
   bool depends_only_on(table_map view_map) 
-  { return marker & MARKER_FULL_EXTRACTION; }
-  int get_extraction_flag() const
-  { return marker & MARKER_EXTRACTION_MASK; }
+  { return get_extraction_flag() & MARKER_FULL_EXTRACTION; }
+   int get_extraction_flag() const
+  {
+    if (basic_const_item())
+      return MARKER_FULL_EXTRACTION;
+    else
+      return marker & MARKER_EXTRACTION_MASK;
+  }
   void set_extraction_flag(int16 flags)
   {
-    marker &= ~MARKER_EXTRACTION_MASK;
-    marker|= flags;
+    if (!basic_const_item())
+    {
+      marker= marker & ~MARKER_EXTRACTION_MASK;
+      marker|= flags;
+    }
   }
   void clear_extraction_flag()
   {
-    marker &= ~MARKER_EXTRACTION_MASK;
-  }
+    if (!basic_const_item())
+      marker= marker & ~MARKER_EXTRACTION_MASK;
+   }
   void check_pushable_cond(Pushdown_checker excl_dep_func, uchar *arg);
   bool pushable_cond_checker_for_derived(uchar *arg)
   {