MDEV-18712 InnoDB indexes are inconsistent with what defined in .frm for table...

MDEV-18712 InnoDB indexes are inconsistent with what defined in .frm for table after rebuilding table with index on blob

when auto-adding a virtual LONG_UNIQUE_HASH_FIELD, fill in
a Virtual_column_info for it, so that fill_alter_inplace_info()
would know we're adding a virtual field (ALTER_ADD_VIRTUAL_COLUMN).

mysql-test/main/long_unique_bugs.result

@@ -10,3 +10,13 @@ create temporary table tmp (a varchar(1024), b int, c int, d int, e linestring,
 load data infile 'load.data' into table tmp;
 delete from tmp;
 drop table t1;
+create table t1 (b blob) engine=innodb;
+alter table t1 add unique (b);
+alter table t1 force;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `b` blob DEFAULT NULL,
+  UNIQUE KEY `b` (`b`) USING HASH
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+drop table t1;

mysql-test/main/long_unique_bugs.test

+--source include/have_innodb.inc
+
 #
 # MDEV-18707 Server crash in my_hash_sort_bin, ASAN heap-use-after-free in Field::is_null, server hang, corrupted double-linked list
 #
@@ -15,3 +17,12 @@ delete from tmp;
 drop table t1;
 --let $datadir= `SELECT @@datadir`
 --remove_file $datadir/test/load.data
+
+#
+# MDEV-18712 InnoDB indexes are inconsistent with what defined in .frm for table after rebuilding table with index on blob
+#
+create table t1 (b blob) engine=innodb;
+alter table t1 add unique (b);
+alter table t1 force;
+show create table t1;
+drop table t1;

sql/sql_table.cc

@@ -3321,6 +3321,8 @@ static Create_field * add_hash_field(THD * thd, List<Create_field> *create_list,
   cf->length= cf->char_length= cf->pack_length= HA_HASH_FIELD_LENGTH;
   cf->invisible= INVISIBLE_FULL;
   cf->pack_flag|= FIELDFLAG_MAYBE_NULL;
+  cf->vcol_info= new (thd->mem_root) Virtual_column_info();
+  cf->vcol_info->stored_in_db= false;
   uint num= 1;
   LEX_CSTRING field_name;
   field_name.str= (char *)thd->alloc(LONG_HASH_FIELD_NAME_LENGTH);

sql/unireg.cc

@@ -691,7 +691,7 @@ static bool pack_vcols(String *buf, List<Create_field> &create_fields,
 
   for (uint field_nr=0; (field= it++); field_nr++)
   {
-    if (field->vcol_info)
+    if (field->vcol_info && field->vcol_info->expr)
       if (pack_expression(buf, field->vcol_info, field_nr,
                           field->vcol_info->stored_in_db
                           ? VCOL_GENERATED_STORED : VCOL_GENERATED_VIRTUAL))