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

[zimoun <zimon.toutoune@gmail.com>]

Hi Gábor,


On Thu, 12 Dec 2019 at 21:54, Gábor Boskovits <boskovits@gmail.com> wrote:

> zimoun <zimon.toutoune@gmail.com> 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