-d flag removes contents of already existing directory, though does not say in README

Using the -d or --plugin-download-directory will remove the directory/contents specified with the flag, even if there are contents there. This is not reflected in the README:

--plugin-download-directory or -d: (optional) Path to the directory in which to install plugins, which can also be set via
 the PLUGIN_DIR environment variable. Directory will be created if it does not exist. If no directory is entered, directory
 will default to C:\ProgramData\Jenkins\Reference\Plugins if detected OS is Windows, or /usr/share/jenkins/ref/plugins 
otherwise.

I don’t believe this should be the default behavior. There should be at least a warning letting the user know that it whatever is there will be removed or that location already exists. I just found this out the hard way as I pointed -d to my current plugins folder which caused the removal of all of my plugins, and now Jenkins wants to uninstall them on next reboot since they’re missing.

Please feel free to correct me if I have something wrong.

[timja]

This was a quick fix to an issue we had with failed plugin downloads never being cleared up.

The proper fix would either be:

• Download plugins to a tmp directory and move when successful
• delete failed downloads only

[ricksbrown]

IMHO the directory should be deleted so that it contains only the plugins listed in the YAML file (and the resulting dependency tree).

Otherwise plugin-installation-manager-tool cannot be used in IasC to uninstall plugins when they are removed from config, it can only ever add new plugins, leaving unlisted ones installed forever.

Also I would DL them all to tmp, and only move them when the entire list is successful - i.e. the entire operation is atomically successful or atomically fails.