Re: Supporting multiline Package-Requires header

[Artur Malabarba <bruce.connor.am@gmail.com>]

2015-08-11 9:44 GMT+01:00 Nicolas Richard <youngfrog@members.fsf.org>:
>>> I understand that the new tools will work with old files, but will the
>>> new files work with the old tools ? i.e. will it be possible to install
>>> these packages to emacs 24.5 ?
>>
>> No. A package that writes it like this will only be (properly) installable on Emacs 25 and up.
>>
>> Of course I'd never drop support for Emacs 24 on one of my packages
>> just for the sake of this minor feature. But once I start routinely
>> requiring Emacs 25.1 because of other features, I'll be glad to have
>> this as a bonus.
>
> It makes sense. My worry is also that emacs-24 must have a way to
> understand that the package is "not installable". e.g. we don't want
> list-packages to suddenly break on older emacsen (I have no idea if this
> can actually happen).

I don't think this can happen. `list-packages' receives information
from the archives, it doesn't manually parse remote packages (it
parses already-installed packages, but if it has been installed
already then it must be compatible). As long as the archive servers
are using the latest Emacs release, they'll know that the package
requires Emacs 25, and they'll provide that information to the user
during `list-packages'.

(And besides, even if the archive is using Emacs 24, or if the user
tries to manually install the package, they'll be immediately greeted
with an error, telling them something is wrong.)