On Thursday, 31 December 2020 09:31:13 GMT Neil Bothwick wrote:
> On Thu, 31 Dec 2020 08:34:42 +0100, n952162 wrote:
> > Why do you specify -1?  That's the most common advice I get for avoiding
> > slot-conflicts, but I can't imagine a system without cups.
> 
> To avoid adding to your world file. If a package needs to be in @world,
> it will already be there to -1 will be harmless. In the case of CUPS, you
> don't want it in world as it is a dependency of any program that wants to
> be able to print.

Yes, what Neil sagely advised.  :-)

I suggest you make it a rule to always run emerge for any individual package 
atom with -1, unless you *really* intend to install such a package yourself 
and it has not been already installed as a dependency for other package(s).  
If you do not use -1 the package you emerge will be added in your world file 
and then you could end up fighting against portage sooner or later.

Imagine a hypothetical scenario where one day CUPS is deprecated and replaced 
by the oh-so-marvellous latest and greatest CUPS-ng.  You try to update your 
system, but come up against a blocker because the recently deprecated old CUPS 
now clashes with CUPS-ng.  The old CUPS is in your world file, because you 
added it there by running emerge without -1 and consequently portage cannot 
override your choice and unmerge it to replace it with CUPS-ng.  Portage will 
now throw a wobbly, alerting you to a blocker you must resolve yourself.

This is why you were advised in previous messages related to the recent python 
updates to make sure among other things no python packages have inadvertently 
ended up in your world file.  Unless you're a developer with specific python 
requirements, you would not want python which is both a @system set and 
potentially @world set dependency to end up in there.