ASAN SEGV in get_prefix upon modifying base column type with existing indexed virtual column

CREATE TABLE t1 ( 

    a TIMESTAMP,

    b TIMESTAMP AS (a) VIRTUAL,

    KEY (b)

);

ALTER TABLE t1 MODIFY a BLOB FIRST;

# Cleanup

DROP TABLE t1;

ASAN:DEADLYSIGNAL

=================================================================

==21894==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x5630df985385 bp 0x7f90a7deff50 sp 0x7f90a7deff20 T5)

    #0 0x5630df985384 in get_prefix /data/src/10.4/sql-common/my_time.c:328

    #1 0x5630df9855ed in find_body /data/src/10.4/sql-common/my_time.c:357

    #2 0x5630df9882b1 in str_to_datetime_or_date /data/src/10.4/sql-common/my_time.c:880

    #3 0x5630de1b60a0 in Temporal::ascii_to_datetime_or_date(st_mysql_time_status*, char const*, unsigned long, date_mode_t) (/data/bld/10.4-asan-nightly/bin/mysqld+0x155f0a0)

    #4 0x5630de1aceda in Temporal::str_to_datetime_or_date(THD*, st_mysql_time_status*, char const*, unsigned long, charset_info_st const*, date_mode_t) /data/src/10.4/sql/sql_time.cc:393

    #5 0x5630de3a3f15 in Temporal_with_date::Temporal_with_date(THD*, st_mysql_time_status*, char const*, unsigned long, charset_info_st const*, date_mode_t) /data/src/10.4/sql/sql_type.h:1827

    #6 0x5630de3a4d21 in Datetime::Datetime(THD*, st_mysql_time_status*, char const*, unsigned long, charset_info_st const*, date_mode_t) (/data/bld/10.4-asan-nightly/bin/mysqld+0x174dd21)

    #7 0x5630de38fd86 in Type_handler_string_result::Item_temporal_precision(THD*, Item*, bool) const /data/src/10.4/sql/sql_type.cc:6343

    #8 0x5630de3aa822 in Type_handler_string_result::Item_datetime_precision(THD*, Item*) const /data/src/10.4/sql/sql_type.h:4651

    #9 0x5630de3b087c in Item::datetime_precision(THD*) /data/src/10.4/sql/item.h:1639

    #10 0x5630de5a9a0f in Field_timestamp::conversion_depends_on_sql_mode(THD*, Item*) const /data/src/10.4/sql/field.cc:5070

    #11 0x5630de58c4b8 in Field::check_vcol_sql_mode_dependency(THD*, vcol_init_mode) const /data/src/10.4/sql/field.cc:1411

    #12 0x5630de15fc48 in parse_vcol_defs(THD*, st_mem_root*, TABLE*, bool*, vcol_init_mode) /data/src/10.4/sql/table.cc:1155

    #13 0x5630de176e9b in open_table_from_share(THD*, TABLE_SHARE*, st_mysql_const_lex_string const*, unsigned int, unsigned int, unsigned int, TABLE*, bool, List<String>*) /data/src/10.4/sql/table.cc:3798

    #14 0x5630de0e9763 in create_table_for_inplace_alter /data/src/10.4/sql/sql_table.cc:9302

    #15 0x5630de0ed1dc in mysql_alter_table(THD*, st_mysql_const_lex_string const*, st_mysql_const_lex_string const*, HA_CREATE_INFO*, TABLE_LIST*, Alter_info*, unsigned int, st_order*, bool) /data/src/10.4/sql/sql_table.cc:10025

    #16 0x5630de24e1bf in Sql_cmd_alter_table::execute(THD*) /data/src/10.4/sql/sql_alter.cc:508

    #17 0x5630ddebd241 in mysql_execute_command(THD*) /data/src/10.4/sql/sql_parse.cc:6094

    #18 0x5630ddec82b2 in mysql_parse(THD*, char*, unsigned int, Parser_state*, bool, bool) /data/src/10.4/sql/sql_parse.cc:7912

    #19 0x5630dde9fa09 in dispatch_command(enum_server_command, THD*, char*, unsigned int, bool, bool) /data/src/10.4/sql/sql_parse.cc:1841

    #20 0x5630dde9c758 in do_command(THD*) /data/src/10.4/sql/sql_parse.cc:1359

    #21 0x5630de23838d in do_handle_one_connection(CONNECT*) /data/src/10.4/sql/sql_connect.cc:1412

    #22 0x5630de237d41 in handle_one_connection /data/src/10.4/sql/sql_connect.cc:1316

    #23 0x5630df81f05d in pfs_spawn_thread /data/src/10.4/storage/perfschema/pfs.cc:1862

    #24 0x7f90b26034a3 in start_thread (/lib/x86_64-linux-gnu/libpthread.so.0+0x74a3)

    #25 0x7f90b0b4bd0e in __clone (/lib/x86_64-linux-gnu/libc.so.6+0xe8d0e)

AddressSanitizer can not provide additional info.

SUMMARY: AddressSanitizer: SEGV /data/src/10.4/sql-common/my_time.c:328 in get_prefix

Thread T5 created by T0 here:

    #0 0x7f90b2849f59 in __interceptor_pthread_create (/usr/lib/x86_64-linux-gnu/libasan.so.3+0x30f59)

    #1 0x5630df81f44a in spawn_thread_v1 /data/src/10.4/storage/perfschema/pfs.cc:1912

    #2 0x5630ddbdf5e8 in inline_mysql_thread_create /data/src/10.4/include/mysql/psi/mysql_thread.h:1268

    #3 0x5630ddbf444f in create_thread_to_handle_connection(CONNECT*) /data/src/10.4/sql/mysqld.cc:6240

    #4 0x5630ddbf4b32 in create_new_thread(CONNECT*) /data/src/10.4/sql/mysqld.cc:6310

    #5 0x5630ddbf4ebd in handle_accepted_socket(st_mysql_socket, st_mysql_socket) /data/src/10.4/sql/mysqld.cc:6408

    #6 0x5630ddbf5b0f in handle_connections_sockets() /data/src/10.4/sql/mysqld.cc:6566

    #7 0x5630ddbf3cd0 in mysqld_main(int, char**) /data/src/10.4/sql/mysqld.cc:5898

    #8 0x5630ddbdd4cf in main /data/src/10.4/sql/main.cc:25

    #9 0x7f90b0a832e0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202e0)

==21894==ABORTING

commit c924e39fab54ed63a427c27d39778eacd961764b

Author: Alexander Barkov

Date:   Fri Sep 13 11:04:23 2019 +0400

    MDEV-18153 Assertion `0' or Assertion `btr_validate_index(index, 0)' failed in row_upd_sec_index_entry or error code 126: Index is corrupted upon UPDATE with TIME_ROUND_FRACTIONAL