[asdf-devel] Proposal for improved support for versions of systems

[Faré]

>>: Faré
>: Vsevolod Dyomkin
> Dear

>> If I may suggest a simpler, cheaper and more useful strategy for
>> helping with the version management of Lisp software, it would be to
>> automatically produce Debian, RPM or Nix packages from ASDF
>> specifications, and let those tools do the rest of the integration.
>>
I reiterate my suggestion.

>> Why only three integers? While you're at it, why not accept the whole
>> range of Debian or RPM version comparisons?
>
> Actually, the number of integers is not limited, it's just that this is the
> default practice and currently available predicates only take into account
> the first two.  So the internal representation is a list of integers.  But
> the user can specify versions in many different formats, like "1.2.3" or
> even 1.2 (float number).  Moreover it's possible to build adapters for more
> representations by defining methods for the generic function PROPER-VERSION.
>
Once again, it would be better if you just agreed to the de facto "standard"
of either Debian or RPM versioning. But once again, I think this code should
NOT be part of ASDF.

> To clarify my point: there are cases of libraries, that use the read-eval
> syntax in version definitions, most notable of which are Edi Weitz's and
> Cyrus Harmon's.  I agree here with Robert Goldman, that this is a little
> contrary to the declarative nature of DEFSYSTEM form.  Still it is not a
> problem with neither the existing, nor the proposed variants.  It's just
> that in the FIND-SYSTEM pipeline such version declarations (or rather
> evaluations) won't be counted (i.e. considered equal to wildcard version).
> But during the evaluation of DEFSYSTEM form itself the version would be
> properly evaluated.  So this peculiarity will effect the new behavior, but
> not the old, that is why I don't consider it a problem: if someone would
> like to use the new behavior, he is free to adapt his code, otherwise he can
> leave it as is and no problems would arise.
>
That I agree with. We should be sure to provide a simple incremental upgrade
path from where we are to wherever we go.

>> > Besides, an incompatible change is introduced to FIND-SYSTEM.  The
>> > ERROR-P
>> > optional argument is removed, so plain NIL is unconditionally returned,
>> > when
>> > system is not found, and VERSION and VERSION-P optional arguments are
>> > added
>> > instead.
>> This sounds very bad to me. What is the use case?
>
> The use case is that we can now (oos 'load 'system :version "1.2.3") or
> write in defsystem :depends-on (system "1.2.3" :above).  As all those
> user-facing facilities use FIND-SYSTEM as the underlying tool.
> Independently from adding VERSION and VERSION-P I would still argue to
> remove ERROR-P argument, as it adds unnecessary complexity.  There's only
> one place in the original ASDF code (OPERATE), where it's expected and it is
> easily handled in the caller.
>
This is not a use case. What is a high-level situation in which a user or
developer may want to use versioning, and why should this situation be
solved using FIND-SYSTEM?

>> How does that affect
>> the semantics of find-system? Can there now be many instances of a
>> system in the source-registry?
>
> The semantics is the following: only zero or one instance of a system with a
> particular name can be in memory (in *defined-systems*) — just like before.
> The current behavior is that if some system is loaded, there's no
> possibility to load the new version.  The new behavior is that, if
> FIND-SYSTEM is forced to load the different version of the system, a
> continuable error is signaled, that informs the user of the situation and
> it's possible either to abort or continue.  If the user continues, the new
> definition is loaded instead of the old.
>
That sounds both complex to implement, for little value to a user.

>> Does find-system now have to grovel for
>> *all* these instances, load the .asd files to determine the version
>> and pick the most recent one by default? That's C R A Z Y.
>
> Yeah, now SYSDEF-CENTRAL-REGISTRY-SEARCH et al. return a list of found ASD
> files instead of the first one.  Then the most suitable is chosen by these
> criteria:
> * if no version is specified it will be either the one already in memory, or
> the first one in the list
> * if version is specified it will be the one in memory, if
> VERSION-SATISFies, or the first from a list, for which version satisfies
>
That's both expensive and backwards incompatible with current API.

I propose instead that a completely different API be used, that computes and/or
checks a source-registry from some specification and a database of available
system versions. i.e. layer something on top of ASDF without modifying anything
about ASDF proper.

>> Note that the current interface of find-system seems to be copied from
>> that of find-class.
>
> Hmm, I see.  I still don't support such decision, but maybe I just not
> understand something...
>
It's just a matter of backwards compatibility. If we're going to change how
things work, I'd rather we provide a new API and declare the old one obsolete
than break backwards compatibility gratuitously. Also, I'm not convinced by
this :VERSION interface. Version matching is not a local problem to be
solved by adding :VERSION arguments to local function calls, but a global
problem to be approached by collecting (in)equations about available versions,
solving these inequations, and producing a source-registry (possibly pointing
to a single generated link farm) as a solution.

>> I'd rather ASDF has only one test framework, if possible one with few
>> dependencies if at all.
>
> I agree.  If there's one already chosen, I'll stick to it.  as I've said,
> when I've started this work, I didn't find any tests, so I used my own
> approach.  By the way MUTEST is dependency-free.
>
I haven't looked at MUTEST yet. I'll have to do it soon. If you're willing
to migrate all existing tests to it -- why not.

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