MDEV-26220 Server crashes with indexed by prefix virtual column

Server crashes in Field::register_field_in_read_map upon select from
partitioned table with indexed by prefix virtual column.

After several read-mark fixes a problem has surfaced:
Since KEY (c(10),a) uses only a prefix of c, a new field is created,
duplicated from table->field[3], with a new length. However,
vcol_inco->expr is not copied.

Therefore, (*key_info)->key_part[i].field->vcol_info->expr was left NULL
in ha_partition::index_init().

Solution: initialize vcols before key initialization

Also key initialization is moved to a function.

3 files changed, 34 insertions, 0 deletions

diff --git a/mysql-test/suite/gcol/inc/gcol_partition.inc b/mysql-test/suite/gcol/inc/gcol_partition.inc
index 4e4af4f0023..50a743c0153 100644
--- a/mysql-test/suite/gcol/inc/gcol_partition.inc
+++ b/mysql-test/suite/gcol/inc/gcol_partition.inc
@@ -169,3 +169,15 @@ CREATE TABLE t1 (
 INSERT INTO t1 () VALUES (),();
 UPDATE t1 SET a = 0 WHERE b IS NULL ORDER BY pk;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-26220 Server crashes with indexed by prefix virtual column
+--echo #
+
+CREATE TABLE t1 (pk INT PRIMARY KEY, a INT, b CHAR(20), c CHAR(20) AS (b),
+                 KEY (c(10),a)) PARTITION BY HASH(pk);
+INSERT INTO t1 (pk,a,b) VALUES (1,10,'foo'),(2,11,'baz');
+SELECT a FROM t1;
+
+# Cleanup
+DROP TABLE t1;
diff --git a/mysql-test/suite/gcol/r/gcol_partition_innodb.result b/mysql-test/suite/gcol/r/gcol_partition_innodb.result
index d3f211c9b9a..e61c0a26417 100644
--- a/mysql-test/suite/gcol/r/gcol_partition_innodb.result
+++ b/mysql-test/suite/gcol/r/gcol_partition_innodb.result
@@ -104,6 +104,17 @@ INSERT INTO t1 () VALUES (),();
 UPDATE t1 SET a = 0 WHERE b IS NULL ORDER BY pk;
 DROP TABLE t1;
 #
+# MDEV-26220 Server crashes with indexed by prefix virtual column
+#
+CREATE TABLE t1 (pk INT PRIMARY KEY, a INT, b CHAR(20), c CHAR(20) AS (b),
+KEY (c(10),a)) PARTITION BY HASH(pk);
+INSERT INTO t1 (pk,a,b) VALUES (1,10,'foo'),(2,11,'baz');
+SELECT a FROM t1;
+a
+11
+10
+DROP TABLE t1;
+#
 # MDEV-16980 Wrongly set tablename len while opening the
 #                table for purge thread
 #
diff --git a/mysql-test/suite/gcol/r/gcol_partition_myisam.result b/mysql-test/suite/gcol/r/gcol_partition_myisam.result
index 75e216f903b..e54b0ad83c6 100644
--- a/mysql-test/suite/gcol/r/gcol_partition_myisam.result
+++ b/mysql-test/suite/gcol/r/gcol_partition_myisam.result
@@ -101,6 +101,17 @@ KEY (b,d)
 INSERT INTO t1 () VALUES (),();
 UPDATE t1 SET a = 0 WHERE b IS NULL ORDER BY pk;
 DROP TABLE t1;
+#
+# MDEV-26220 Server crashes with indexed by prefix virtual column
+#
+CREATE TABLE t1 (pk INT PRIMARY KEY, a INT, b CHAR(20), c CHAR(20) AS (b),
+KEY (c(10),a)) PARTITION BY HASH(pk);
+INSERT INTO t1 (pk,a,b) VALUES (1,10,'foo'),(2,11,'baz');
+SELECT a FROM t1;
+a
+11
+10
+DROP TABLE t1;
 DROP VIEW  IF EXISTS v1,v2;
 DROP TABLE IF EXISTS t1,t2,t3;
 DROP PROCEDURE IF EXISTS p1;