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

["Gábor Boskovits" <boskovits@gmail.com>]

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Hello Konrad,

Konrad Hinsen <konrad.hinsen@fastmail.net> ezt írta (időpont: 2019. dec.
17., Ke 7:52):

> On 16/12/2019 23:09, Ludovic Courtès wrote:
> > 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.
> > That sounds like a good plan to me.
> >
> > #4 is the trickiest, and I think it’d be good to give users a bit of
> > time so they can start adjusting before deprecation is in effect.
>
> #4 is trickiest for another reason: there is no future-proof use of
> "guix environment" that works right now and will continue to work. Nor
> is there any way to see, when looking at a command line, whether it's
> old-style or new-style, if neither --ad-hoc nor --inputs-of are present.
> This means that all existing documentation (tutorials etc.) will become
> misleading in the future. Worse, even documentation written today, in
> full awareness of a coming change, can't do better than saying "watch
> out, this will do something else in the future".
>
> The first rule of backwards-compatibility is: never change the meaning
> of an existing valid command/API. Add new valid syntax, deprecate old
> valid syntax, but don't change the meaning of something that was and
> will be valid.
>
> How about a more drastic measure: deprecate "guix environment" and
> introduce a new subcommand with the desired new behaviour?
>
That is also the other option I was thinking about. Do you have any good
idea in mind as how to call it? Of course the classic guix environment2
comes to my mind, but it does not look very appealing to me.

>
>
> Cheers,
>
>    Konrad.
>
Best regard,
g_bor

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