bug#38529: Make --ad-hoc the default for guix environment proposed deprecation mechanism

[Gábor Boskovits]

Hello,

Let me try again :)

zimoun <address@hidden> ezt írta (időpont: 2019. dec. 13., P, 13:02):
>
> Hi Gábor,
>
>
> On Thu, 12 Dec 2019 at 21:54, Gábor Boskovits <address@hidden> wrote:
>
> > zimoun <address@hidden> ezt írta (időpont: 2019. dec. 12., Csü 17:47):
>
> >> Maybe I miss a point. Is the aim to conserve the "--ad-hoc" option
> >> with a different effect? Or why do we want to conserve this option
> >> name?
> >> It appears to me simpler to give another name, for example
> >> "--inputs-of". And it is more meaningful.
> >
> > Sorry for the confusion. Ad-hoc should be retained with the same effect, so 
> > that we do not break existing scripts.
> > Renamin the option would be ok. It even makes sense to me.
>
> What I propose is:
>
>   - keep the option "--ad-hoc" with the current behavior; so same effect
>   - add a new option "--inputs-of" with the new behavior; name more meaningful
>   - and two env variables; to not break existing scripts
>
>
> >> First, when "--ad-hoc" is used then it reports a warning: deprecated
> >> option and falls in the current behavior.
> >> When "--inputs-of" is used then it falls in the new behavior.
> >> Therefore, no needs of the ugly "--ignore-deprecated-ad-hoc".
> >
> > That could be done. The problem is caused by uses of guix environment that 
> > does not use any of these options. Those mean different things after the 
> > change.
>
> The transition to such use-case was described below with the
> introduction of 2 env variables. :-)
>
>
> >>  # Alice
> >>  $ guix environment foo --ad-hoc bar
> >>  Warning: deprecated... explanations...
> >>                instead use:
> >>                 guix environment bar --inputs-of foo
> >>
> >>  # Bob
> >>  $ guix environment bar --inputs-of foo
> >>
> >>
> >> Second, the previous "guix environment foo" (dependencies of foo) is
> >> inconsistent with the new "guix environment bar" (only the package
> >> bar). Therefore, let introduce the GUIX_ENVIRONMENT_DEPRECATED
> >> variable to distinguish both, as you said.
> >
> > Ok.
>
> It is the easy part. ;-)
>
>
> Now the hard part: avoid to break existing scripts.
>
> >>  # Alice
> >>  $ guix environment foo
> >>  Warning: previous behavior requires GUIX_ENVIRONMENT_DEPRECATED=1
> >>                turn off the warning: GUIX_ENVIRONMENT_NOWARNING=1
> >>
> >> And Alice has now a new shell with the package foo. If she wants the
> >> dependencies, she has two options:
> >>
> >> $ GUIX_ENVIRONMENT=1 guix environment foo
> >> or
> >> $ guix environment --inputs-of foo
> >>
> >>
> >>  # Bob
> >>  $ guix environment bar
> >>  Warning: previous behavior requires GUIX_ENVIRONMENT
> >>
> >> And if Bob is annoyed by the warnings each time, he globally turns off
> >> with the variable GUIX_ENVIRONMENT_NOWARNING=1.
> >>
> >>
> >> Couple of months later -- after the period adoption -- we remove the
> >> variables GUIX_ENVIRONMENT_NOWARNING and GUIX_ENVIRONMENT_DEPRECATED;
> >> still keeping the warning with the "--ad-hoc" option. And then, after
> >> we can remove the "--ad-hoc" option if required.
>
>
> > We could recommend simply to use something like:
> > GUIX_ENVIRONMENT_DEPRECATED=0 guix environment ...
> > Instead in existing scripts that are fixed to use the new syntax. This 
> > indeed looks like a better solution, and it is less of a maintenance 
> > burden. Good idea.
>
> My point is: the new variable GUIX_ENVIRONMENT_DEPRECATED should only
> be used by the scripts that call "guix environment pkg" without the
> options "--ad-hoc" or "--inputs-of". And I think that it represents
> really few scripts in real life. :-)
>
>
> > Summarizing:
> > Introduce the environment variable.
> > For fixed scripts recommend unsetting the environment variable.
>
> I am not to get your plan. :-)
>
>
> Cheers,
> simon

So in a more algorithmic manner:
1. if ad-hoc and inputs-of is present at the same invocation: fail
hard. (With an error like incompatible options present)
2. if only ad-hoc is present, then print a deprecation warning (yes,
we could make this suspendable with an environment variable, like you
described)
3. if only inputs-of present, then do the new behaviour.
4. if neither ad-hoc nor inputs-of present then
  a. if GUIX_ENVIRONMENT_DEPRECATED is 1: do the current behaviour,
  b. if GUIX_ENVIRONMENT_DEPRECATED is undefined, or is not 1: do the
new behaviour.

This would minimze friction, as there will be a few scripts falling under 4.
This would also allow mirgating such scripts one by one. be defining
GUIX_ENVIRONMENT_DEPRECATED to 1 in some startup file, and using
GUIX_ENVIRONMENT_DEPRECATED=0 guix environment ... in scripts that are
fixed to use the new syntax.


What do you think?

Best regards,
g_bor
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