MDEV-21787 Alter table failure tries to access uninitialized column

- Problem is that failure of inplace DDL tries to access the
uninitialized column. This is caused by MDEV-19606 (commit 0274ab1d).
Fix is that InnoDB should use column while freeing the index when index
is completely initialized.

mysql-test/suite/innodb/r/instant_alter_limit,32k.rdiff

---- instant_alter_limit.result
-+++ instant_alter_limit.result
-@@ -42,5 +42,5 @@
+--- instant_alter_limit.result	2020-05-26 18:01:27.377946439 +0530
++++ instant_alter_limit,32k.reject	2020-05-26 19:59:19.743877366 +0530
+@@ -43,5 +43,12 @@
  FROM information_schema.global_status
  WHERE variable_name = 'innodb_instant_alter_column';
  instants
 -502
 +506
  DROP TABLE t;
++#
++# MDEV-21787 Alter table failure tries to access uninitialized column
++#
++CREATE TABLE t1(f1 INT PRIMARY KEY, f2 TEXT GENERATED ALWAYS AS (SUBSTR(f4, 1, 400)), f3 VARCHAR(500), f4 TEXT)ENGINE=InnoDB ROW_FORMAT=Compact;
++ALTER TABLE t1 ADD UNIQUE KEY (f2(9));
++ALTER TABLE t1 ADD COLUMN f5 TEXT, ALGORITHM=INPLACE;
++DROP TABLE t1;

mysql-test/suite/innodb/r/instant_alter_limit,4k.rdiff

---- instant_alter_limit.result
-+++ instant_alter_limit.result
+--- instant_alter_limit.result	2020-05-26 18:01:27.377946439 +0530
++++ instant_alter_limit,4k.reject	2020-05-26 20:17:53.314736548 +0530
 @@ -5,6 +5,276 @@
  ENGINE=InnoDB;
  INSERT INTO t VALUES(1,2,3,4,5);
@@ -295,10 +295,19 @@
  ALTER TABLE t ADD COLUMN b INT NOT NULL, ALGORITHM=INSTANT;
  ERROR 0A000: ALGORITHM=INSTANT is not supported for this operation. Try ALGORITHM=INPLACE
  SELECT variable_value-@old_instant instants
-@@ -43,5 +319,5 @@
+@@ -43,5 +319,14 @@
  FROM information_schema.global_status
  WHERE variable_name = 'innodb_instant_alter_column';
  instants
 -502
 +474
  DROP TABLE t;
++#
++# MDEV-21787 Alter table failure tries to access uninitialized column
++#
++CREATE TABLE t1(f1 INT PRIMARY KEY, f2 TEXT GENERATED ALWAYS AS (SUBSTR(f4, 1, 400)), f3 VARCHAR(500), f4 TEXT)ENGINE=InnoDB ROW_FORMAT=Compact;
++ALTER TABLE t1 ADD UNIQUE KEY (f2(9));
++ALTER TABLE t1 ADD COLUMN f5 TEXT, ALGORITHM=INPLACE;
++Warnings:
++Warning	139	Row size too large (> 1982). Changing some columns to TEXT or BLOB or using ROW_FORMAT=DYNAMIC or ROW_FORMAT=COMPRESSED may help. In current row format, BLOB prefix of 768 bytes is stored inline.
++DROP TABLE t1;

mysql-test/suite/innodb/r/instant_alter_limit,64k.rdiff

---- instant_alter_limit.result
-+++ instant_alter_limit.result
-@@ -42,5 +42,5 @@
+--- instant_alter_limit.result	2020-05-26 18:01:27.377946439 +0530
++++ instant_alter_limit,64k.reject	2020-05-26 20:00:22.499711222 +0530
+@@ -43,5 +43,12 @@
  FROM information_schema.global_status
  WHERE variable_name = 'innodb_instant_alter_column';
  instants
 -502
 +506
  DROP TABLE t;
++#
++# MDEV-21787 Alter table failure tries to access uninitialized column
++#
++CREATE TABLE t1(f1 INT PRIMARY KEY, f2 TEXT GENERATED ALWAYS AS (SUBSTR(f4, 1, 400)), f3 VARCHAR(500), f4 TEXT)ENGINE=InnoDB ROW_FORMAT=Compact;
++ALTER TABLE t1 ADD UNIQUE KEY (f2(9));
++ALTER TABLE t1 ADD COLUMN f5 TEXT, ALGORITHM=INPLACE;
++DROP TABLE t1;

mysql-test/suite/innodb/r/instant_alter_limit,8k.rdiff

---- instant_alter_limit.result
-+++ instant_alter_limit.result
+--- instant_alter_limit.result	2020-05-26 18:01:27.377946439 +0530
++++ instant_alter_limit,8k.reject	2020-05-26 20:19:50.881869095 +0530
 @@ -5,6 +5,28 @@
  ENGINE=InnoDB;
  INSERT INTO t VALUES(1,2,3,4,5);
@@ -47,10 +47,17 @@
  ALTER TABLE t ADD COLUMN b INT NOT NULL, ALGORITHM=INSTANT;
  ERROR 0A000: ALGORITHM=INSTANT is not supported for this operation. Try ALGORITHM=INPLACE
  SELECT variable_value-@old_instant instants
-@@ -43,5 +71,5 @@
+@@ -43,5 +71,12 @@
  FROM information_schema.global_status
  WHERE variable_name = 'innodb_instant_alter_column';
  instants
 -502
 +492
  DROP TABLE t;
++#
++# MDEV-21787 Alter table failure tries to access uninitialized column
++#
++CREATE TABLE t1(f1 INT PRIMARY KEY, f2 TEXT GENERATED ALWAYS AS (SUBSTR(f4, 1, 400)), f3 VARCHAR(500), f4 TEXT)ENGINE=InnoDB ROW_FORMAT=Compact;
++ALTER TABLE t1 ADD UNIQUE KEY (f2(9));
++ALTER TABLE t1 ADD COLUMN f5 TEXT, ALGORITHM=INPLACE;
++DROP TABLE t1;

mysql-test/suite/innodb/t/instant_alter_limit.test

@@ -60,3 +60,17 @@ FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 
 DROP TABLE t;
+
+--echo #
+--echo # MDEV-21787 Alter table failure tries to access uninitialized column
+--echo #
+CREATE TABLE t1(f1 INT PRIMARY KEY, f2 TEXT GENERATED ALWAYS AS (SUBSTR(f4, 1, 400)), f3 VARCHAR(500), f4 TEXT)ENGINE=InnoDB ROW_FORMAT=Compact;
+ALTER TABLE t1 ADD UNIQUE KEY (f2(9));
+let $error_code = 0;
+let $innodb_page_size = `SELECT @@INNODB_PAGE_SIZE`;
+if ($innodb_page_size == 4k) {
+ let $error_code= ER_TOO_BIG_ROWSIZE;
+}
+--error $error_code
+ALTER TABLE t1 ADD COLUMN f5 TEXT, ALGORITHM=INPLACE;
+DROP TABLE t1;

storage/innobase/include/dict0mem.h

@@ -1203,7 +1203,7 @@ struct dict_index_t {
   @param   whether to reset fields[].col */
   void detach_columns(bool clear= false)
   {
-    if (!has_virtual())
+    if (!has_virtual() || !cached)
       return;
     for (unsigned i= 0; i < n_fields; i++)
     {