Every time I install a new TeX Live version (the "full" one) on Ubuntu, I encounter some lack of backward compatibility (e.g. missing packages or changed commands in existing packages) and some of my LaTeX projects stop working. Sometimes it takes a lot of time to understand how to fix the problem.
What is a proper way of dealing with such issues? Is there a list of packages that were removed in a new "full" TeX Live version, compared to the previous one?
To be more concrete, this time I have a problem with enumitem package, which is not included TeX Live 2018 and cannot be installed with tlmgr.
Best Answer
Backup old texlive versions!
You asked how to deal with different versions and developments of texlive over the years, especially changing or later deprecated packages. We found out that you got your texlive installation from an unreliable server and you simply installed the missing package.
But texlive 2019 will come soon with changes that may or may not break some documents. How to deal with that?
If you have enough space on your HDD / SDD / whatever, then keep some older installations. I will install texlive 2019 beside texlive 2018 and at a later date delete the really old texlive 2016. All texlive installations reside in .../texlive/year, while my local packages on the level of the machine (not on user-level) reside in .../texlive/texmf-local and remain untouched from the installation of a new texlive.
If texlive 2019 breaks something, I just change the path and am back on texlive 2018 / 17 / 16 for this document.
And to be really on the safe side, I became a member of my local TUG (tex-user-group) and enjoy every year receiving a DVD providing texlive and CTAN. I'm keeping them dry and clean, you never know. OK, I'm not sure texlive 2009 would even run, but at least I could import an old package, just in case...