TYPO3 Core

GeneralUtility::deprecationLog() in 9.5 writes deprecation logs to deprecation file which you can't turn off

(1)

public static function deprecationLog($msg)
    {
        static::writeDeprecationLogFileEntry('GeneralUtility::deprecationLog() will be removed in TYPO3 v10.0, use "trigger_error("Given reason", E_USER_DEPRECATED);" to log deprecations.');
        trigger_error($msg, E_USER_DEPRECATED);
    }

I don't understand why this function does both: use trigger_error and writeDeprecationLogFileEntry. One would be enough, I guess.

Also, writeDeprecationLogFileEntry() writes directly to a logfile which you can't deactivate - AFAICS.

$destination = Environment::getVarPath() . '/log/deprecation_' . self::shortMD5(Environment::getProjectPath() . $GLOBALS['TYPO3_CONF_VARS']['SYS']['encryptionKey']) . '.log';

Some extensions use GeneralUtility::deprecationLog()

(2)

You can turn off (some) deprecation logging via the logging framework (I think)