Bug #96501 MySQL server doesn't start and no error in the log

Description:
If mysqld find that the mysqld-auto.cnf in the data directory has invalid json, whatever is the reason why, it doesn't start and there is NO message in the error log. 
IE :
mysqld-auto.cnf: { "Version" : 1 , "mysql_server" : { "wait_timeout": { "Value : "150" , "Metadata" : { "Timestamp" : 1565455891278414, "User" : "root" , "Host" : "localhost" } } } }
Check the missing quote after the VALUE label

console:
tusa@tusa-dev:/opt/mysql_templates/mysql-8.0.17futex$ ps aux|grep 8113
tusa      8119  0.0  0.0  14224   896 pts/1    S+   12:54   0:00 grep --color=auto 8113
[1]+  Exit 1                  bin/mysqld --defaults-file=./my.cnf

LOG:
no message 

I agree that this file SHOULD NOT NE TOUCH by hand, but at the same time I think the server should raise the error.

How to repeat:
1) start mysqld (8.17)
2) SET PERSIST wait_timeout = X
3) Stop mysqld
4) manually do something stupid on the mysqld-auto.cnf
5) restart mysqld

Suggested fix:
This is a problem in the Json parser, and human stupidity, I just think we should have the server indicating the problem in the error log

Hello Marco Tusa,

Thank you for the report and feedback.
Agree with your conclusion that it should have logged/reported an error. This was expected behavior as documented i.e quoting from manual "Manual changes to the file may result in a parse error at server startup. In this case, the server reports an error and exits". - https://dev.mysql.com/doc/refman/8.0/en/persisted-system-variables.html

regards,
Umesh

Test results - 8.0.17

Attachment: 96501_8.0.17.results (application/octet-stream, text), 15.65 KiB.

- Lowest version checked 8.0.11, similar behavior

Posted by developer:
 
Fixed in 8.0.20.

If the mysqld-auto.cnf file was malformed, the server did not start
(expected), but did not report any error (unexpected).