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
>> 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.