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Re: ELPA policy

From: Filipp Gunbin
Subject: Re: ELPA policy
Date: Tue, 17 Nov 2015 16:01:57 +0300
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (darwin)


On 14/11/2015 04:30 -0600, Stephen Leake wrote:

> Filipp Gunbin <address@hidden> writes:
>> On 12/11/2015 13:52 -0600, Stephen Leake wrote:
>>> I don't see why that is different from depending on a normal ELPA
>>> package.
>> I think it's their dependants what make them different from tarball and
>> normal packages.
>> Emacs core provides API, which others use.  A normal package declares
>> which versions of this API it is supposed to work against.
>> With core packages, Emacs still provides API, but it now consists of a
>> static part (C level & core) and dynamic part (core packages, which can
>> later be updated from ELPA - correct me if I'm wrong).  So, a package
>> should independently define which core version it works agains and which
>> core package(s) version(s) it works against.
> package.el dependencies can only specify a minimum version, not a
> maximum. there is no way that a normal ELPA package can declare that it
> works with seq.el 1.0 but not seq.el 1.1

My words were more of a theoretical speculation rather than discussion
of the current state of package.el.

Some parts of API may be deprecated and removed, so it may be the case
that a current package is not updated instantly and need to use some
previous version of core package.  While having a "single snapshot" of
Emacs + core packages does not cause such issues (even if package does
not specify maximum version which author of course does not know in
advance, the package just doesn’t work and so the user can downgrade to
previous "snapshot", that is, previous Emacs version), separate core
packages update after installation of such a "snapshot" might move
forward and thus break some normal package (and downgrade will not help
- the user will not know what to downgrade - what package? or core
emacs?  And how can I downgrade a single (core) package?).  Just theory,
again.  Ignore if it is irrelevant and I’m complicating things too much.

> So if emacs 25 contains a core ELPA package seq.el 1.0, the declaration
> ;; Package-Requires: ((emacs "25.1"))
> is equivalent to:
> ;; Package-Requires: ((emacs "25.1") (seq "1.0))
> If seq.el 1.1 is later released via the Gnu ELPA server, it will be used
> in either case.

Will the user have the option to continue to use the tarball version
instead of newer ELPA version?  Or choosing which ELPA version to use?
This may be needed when she uses previous major Emacs release, and
current ELPA package version requires newer core APIs.

>>>> We'll probably have to calculate and offer to user which set of the
>>>> multiple core packages' multiple versions suits for multiple normal
>>>> and tarball (perhaps overriden by version from Internet package
>>>> archive) packages, at the same time probably giving the user to
>>>> opportunity to specify her preferred version of each requested
>>>> package. Is it worth the trouble? Or do I understand something wrong?
>>> Emacs does not support multiple versions of packages available
>>> simultaneously; there is only one instance of a package that is first in
>>> load-path.
>>> You can end up with one copy in the installed Emacs distribution, and
>>> one in ~/.emacs.d/elpa. But the elpa one will take precedence; that is
>>> the only one that other packages have to worry about. It either meets
>>> their dependency requirement, or not.
>> Of course, I was talking about the set of available versions which could
>> be installed and from which a user or a package manager should choose.
> I still don't see a problem.
> We have an example of a core ELPA package now; ada-mode. version 4.3 is
> in emacs git; version 5.1.8 is in ELPA (if I ever get 5.x to be fast
> enough on huge files, I'll delete 4.3 from core).
> package.el has no issues with this.
> Similar things can occur when there are different versions of the same
> package in multiple repositories. In that sense, emacs git is just
> another package repository.
> Can you be more explicit about what problem you foresee? Give an example
> of a package that would cause a problem.

For now, I don’t know of any practical examples.  But thanks for your
time on this.


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