Hi Attila! Attila Lendvai <att...@lendvai.name> writes:
>> OK, I've reread this, and it is indeed a risk, that 'unset could leak in >> the case of a serializable configuration making use of a maybe-value >> field of type maybe-symbol. I've added the unit test suggested as >> 97cb43e732a38758c95b7caf3963507188d011cf (currently marked as 'expected >> to fail'). Luckily no current service uses that. > > thank you for that Maxim! > > and sorry for my initial, somewhat reactive, and emotionally driven > response earlier! maintaining a channel with complex services, and > finally getting the changes i needed merged into Guix proper was a > source of frustration for me. No worries. We all get caught in emotions at times. It's not necessarily a bad thing, it's a sign we are invested and care. > i've looked at the current state of the code, and it looks good to me. the > only issues i have left are the following: > > 1) the (eq 'unset ...) scattered around the code; it should be hidden > behind an explicit abstraction, but you yourself mentioned this > already in an earlier mail. i'd call it CONFIGURATION-FIELD-SET? > (instead of MAYBE-SET?). it's longer, but we have completion in emacs, > and it won't be used a gazillion times all around the code either. I had used maybe-value-set? because the maybe values are define via the 'define-maybe' syntax; they are not really part of 'define-configuration' and are sometimes used outside of it, such as in (guix home ssh). > 2) the lack of an abstraction for the unset/unspecified > value. whatever we use as the marker should be hidden behind either an > exported global variable, or a function called > UNSET-CONFIGURATION-FIELD! (or something alike). i should have > introduced these myself, and then your fix would have been as simple > as replacing *UNSPECIFIED* with 'UNSET in the abstraction. An exported variable seems simplest and perhaps less awkward to use, e.g. %unset or similar, although it's a bit ugly that we need to reify an unspecified value :-). > 3) the SYMBOL? corner case that your test captures, but it's not a burning > issue for me (it doesn't affect the user facing API, once the above leakages > are fixed). > > do you agree? if yes, will you implement it, or shall i prepare a patch? I sent a patch somewhere for the maybe-value-set?, see message-id <87bkstnd2d....@gmail.com> up this thread. I'd be happy if you could prepare a patch for the other things mentionned here (an exported symbol). > one more note: sometimes it's useful to have a field with a maybe type > that also has a default, together with the ability to explicitly unset > this field. True. I'd prefer if this never was true for simplicity (a maybe field would not need to take a default value), but the reality is that we may want to set a sane default value while allowing the user to clear the field to have the software use its default behavior. > > an example would be a port specification for a torrent client: it has some > default port, but it's possible to explicitly unset the port value to request > the allocation of a random port at startup. > > to better accommodate for this use case, 2) should probably be > implemented not as an UNSET-FOO! function, but as a global variable > holding the unset value marker. or maybe both? I'd keep things simple with the exported unspecified value rather than both. A single, obvious way to do things is simpler. Thanks, Maxim
