Oracle uses the SQL standard syntax for simple comments: dash-dash starts a comment, the rest of the line is a comment.

DROP PROCEDURE p1;

CREATE PROCEDURE p1 AS

BEGIN

  --This is a comment

  NULL;

END;

/

MariaDB uses non-standard syntaxt: dash-dash-space starts a comment. This is an example of a valid script:

SET sql_mode=DEFAULT;

DROP PROCEDURE p1;

DELIMITER /

CREATE PROCEDURE p1()

BEGIN

  -- This is a comment

END;

/

DELIMITER ;

If I remove the space character after "--", it returns a syntax error:

SET sql_mode=DEFAULT;

DROP PROCEDURE p1;

DELIMITER /

CREATE PROCEDURE p1()

BEGIN

  --This is a comment

END;

/

DELIMITER ;

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '--This is a comment

END' at line 3

That was an intentional design in early MySQL versions:
https://dev.mysql.com/doc/refman/5.7/en/ansi-diff-comments.html

We should add an option to make dash-dash without an extra space start a comment, as it makes migration from Oracle difficult.

Perhaps, a new flag in sql_mode or old_mode can solve the issue.