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[bug#41143] [PATCH 1/2] mapped-devices: Allow target to be list of strin
[bug#41143] [PATCH 1/2] mapped-devices: Allow target to be list of strings
Fri, 25 Sep 2020 11:34:49 +0200
Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux)
Mikhail Tsykalov <firstname.lastname@example.org> skribis:
> On 09.09.2020 23:38, Ludovic Courtès wrote:
>>> diff --git a/gnu/services/base.scm b/gnu/services/base.scm
>>> index 0c154d1c4e..3d09e8220c 100644
>>> --- a/gnu/services/base.scm
>>> +++ b/gnu/services/base.scm
>>> @@ -408,7 +408,10 @@ FILE-SYSTEM."
>>> (define (mapped-device->shepherd-service-name md)
>>> "Return the symbol that denotes the shepherd service of MD, a
>>> (symbol-append 'device-mapping-
>>> - (string->symbol (mapped-device-target md))))
>>> + (string->symbol (string-join
>>> + (let ((t (mapped-device-target md)))
>>> + (if (list? t) t (list t)))
>>> + "-"))))
>> To avoid duplicating the (if (list? t) …) everywhere, I propose instead
>> the following approach:
>> 1. Rename ‘target’ to ‘targets’ (plural) and likewise for the
>> accessor, and agree that it always contains a list;
>> 2. Rename ‘mapped-device’ to ‘%mapped-device’ and add a
>> ‘mapped-device’ backward-compatibility macro that allows for a
>> ‘target’ (singular) field and automatically turns its value into a
>> list. See the ‘origin’ macro in (guix packages) for an example of
>> how to do that (that macro allows users to specify ‘sha256’ instead
>> of ‘hash’).
>> 3. Add a deprecated ‘mapped-device-target’ (singular) that returns the
>> first element returned by ‘mapped-device-targets’.
> While this looks like a good idea, doesn't this break code that
> implements mapped-device and assumes that target is a string. Suddenly
> passing a string to a mapped-device constructor results in a list
> passed to open/close. Also, what functions should do if they expect a
> string but get a list of them? Ignore everything but the first item?
> Implement mandatory check function? Doesn't this change push
> complexity out of mapped-device to implementations of it.
The intent of what I propose above is (1) to not break existing code,
and (2) to avoid duplicating checks and conversions at every call site.
#1 is achieved by providing a deprecated ‘mapped-device-target’
(singular) procedure, for example.
Does that make sense?