Re: The future of 'guix environment'

[Thompson, David]

Thanks for the feedback, everyone.  I'm going to try to address what
everyone has been discussing.

宋文武, I agree with Andreas that making a new command is undesirable and
would just lead to confusion.  I think a single tool can support the
major use cases well.  I'd go so far as to say that I will have failed
if two commands are necessary.  We can always add subcommands to 'guix
environment' itself, if that turns out to be better for usability.  We
will see.

As for a 'guix environment up' command, I think that's worth thinking
about but I'm going to avoid thinking about it too much because we're
still quite a ways off from being able to make this happen.  My
general feeling is the same as Ricardo's, though, that 'guix
environment' should just spawn the services automatically and there
would have to be some notion of "attaching" to an existing session.
This topic deserves a whole separate thread when the time comes.

Ricardo, you are correct that we would lose the ability to use the
guix.scm file for both 'guix environment' and 'guix build'.  In
practice I don't actually use my guix.scm file this way, so I think
it's worth breaking, but maybe you (or someone else) actually uses
this and we should think more about it?

I wasn't very clear about whether ephemeral or cached would be the new
default.  I don't think there is one default for all cases, I think
it's more context sensitive.  When the user specifies --load, I think
caching should be the default because loading such a file means that
you are working on a project for which you'd like a persistent
environment.  When the user specifies ad-hoc packages, caching would
be disabled because most likely they are running a one-off job.  For
example, 'guix environment ruby -- irb' should spawn a Ruby REPL,
discarding the environment when the user exits.  'guix environment
--load=guix.scm' would check for a cached profile, use it if it is
there, otherwise build the profile and cache it for next time.  'guix
environment', without --load or any packages specified, would be
equivalent to 'guix environment --load=guix.scm'.  A little
"convention over configuration" will greatly improve usability, I
think.  There's really only 2 major use cases, and I want those to
work without having to fiddle with a bunch of command line flags.  All
the underlying flags will still be there to fiddle with for those who
are interested.

- Dave