protect/discourage "self update" command invocation

[deronnax]

Hello there.
I worked in several positions of "developer efficiency" in the various companies I worked for, and this role includes a fair amount of Python support to developers. One of the errors I encountered the most is developers messing up their poetry install with poetry self update. I think this command made sense when Poetry was installed with the install script, but nowadays, most Python setups I see have Poetry installed through an external package manager (pipx mostly, sometimes brew, I guess nix could be one), and troubles almost systematically ensue when developers run poetry self update.
If deleting it is not an option, at least an error message offering an option to bypass the protection would be very nice.
In the same way that what pip does with its EXTERNALLY-MANAGED / --break-system-packages option.

[radoering]

I think this command made sense when poetry was installed with the install script

I agree that you should not use self update if you do not use the installer because there are better alternatives. Not sure if you need it if you are using the installer. Personally, I have never used the installer but I believe there are still many Poetry users who use it. It is difficult for me to judge because I normally do not use the self commands but from hearsay I believe the self commands do work for some users at least.

We had a discussion about the self commands in #7872 and decided not to deprecate them. I still think poetry self show (or at least poetry self show plugins) is useful but I do not feel comfortable to decide about the rest.

[Secrus]

I had an idea for self update. We could add a file that the install script creates at the install location that signifies the usage of it. Then on self update, poetry would check for that file and if it is not there, it would prompt for confirmation, warning users that it can be potentially breaking. There are probably some details missing here, but that is the rough idea for a fix.
A similar mechanism could probably be implemented for other self commands, especially the ones that change the Poetry installation state (plugin installs, updates etc)

[deronnax]

That's perfect, I am all for it. I would even suggest to hide the self command if the file is not present, but we can also save this for a future PR. If you can bootstrap a very basic skeleton PR (you probably have a somewhat clear idea of where you want to those things to happen), I can take it over to the finish line (write tests, make CI green, integrate reviews).

[Secrus]

I will see if I will find some time over the weekend, might actually go for it