TYPO3 Core

Invalid value "1" in InstallTool (option: enableDeprecationLog) causes TYPO3 to write deprecation_*.log
Correct behaviour would be not to write anything if the system has been configured incorrectly.

In detail:

InstallTool -> show all configuration -> locate "enableDeprecationLog". Text reads:

Commalist: Enables the logging of deprecated methods and functions. Default is 'file'. The following options are allowed: file [...], devlog [...], console [...]

However, if the value "1" is used (which is an invalid value for enableDeprecationLog according to the text above and the documentation), TYPO3 writes typo3conf/deprecation_[HASH].log

Under normal circumstances, falling back to a specific (or safe) value is legitimate, if the system is misconfigured - but in this case, TYPO3 fills up the disk space if the deprecation_*.log is written, which introduces a risk for some sites (depending on extensions used and individual configuration).

Therefore, using an invalid value for the enableDeprecationLog setting should not write anything.