Q: iTunes Library missing all songs, playlists, movies, etc...

This just happened overnight and you didn't touch the computer?  First I would turn off automatic software updates.  People who do not want to have to think find it convenient but it is kind of like letting your parents come in and clean your room when you're a kid.  All kinds of unexpected and sometimes undesirable results when you return.

Determine if the media files are still present in the iTunes > Media folder. If they are not you will have to restore them from the backup you of course made of your computer before installing new software, or from their original sources.  If they are still there then try one of the following methods to rebuild the database which tells iTunes what media you have in your collection and where it is.

ASC user turingtest2 help document: Empty/corrupt iTunes library after upgrade/crash - https://discussions.apple.com/docs/DOC-6561

If you don't see your content after updating iTunes  - https://support.apple.com/kb/HT203225

I have a similar situation. I run my library off and external drive and back. The Mac Book crashed and restarted and when iTunes reopened the library and playlist was gone. My media is still present on the external drive. I do not have the iTunes library.it file mentioned in the workaround but do have previous versions folder. The problem there is the previous version is 2 months old. If I add that version as instructed I will have a gap. That is my worst case scenario. Is there e a way to read the missing media if using the older previous version.it file besides eyeballing the media folder compared to the restored library? Is there a better option to regain my pre-crash library? Background, my mac is always on and iTunes was always open due to use of home share and apple tv.