Re: [gentoo-pms] Runtime-switchable USE flags

[Michał Górny]

Dnia 2014-06-25, o godz. 12:15:04
Ulrich Mueller <ulm@g.o> napisał(a):

> Hi,
> The council has approved runtime-switchable USE flags [1,2] for
> EAPI 6. Several questions arise:
>
> - If we introduce the feature with an EAPI, we need not care about
>   backwards compatibility. It would be possible to mark runtime
>   switchable flags by some syntax in IUSE, instead of introducing
>   a new variable like IUSE_RUNTIME.
>
>   So far, "%-foo", "@-foo", "*foo", and "foo*" have been suggested as
>   syntax. I don't like the first two because they don't look so nice
>   when combined with "+" or "-" IUSE defaults; mgorny doesn't like the
>   last two because they look like wildcards. Some bikeshedding for the
>   syntax is needed.

"-foo@" or "-foo%" are also possible but that's a poor man's workaround
for current syntax ugliness. The real alternative is:

  <use>
    <flag name="foo" default="off" runtime="yes"/>
  </use>

:P

> - Do we really need all these restrictions for ebuilds listed in [3]?
>   Especially, restricting possible USE dependencies will complicate
>   the spec, and I don't see the benefit of such a restriction.

The specific rules in GLEP were intended to allow catching mistakes
easily. It's easy to make repoman complain when it sees runtime flag
in SRC_URI or portage to complain when 'use' is queried using a runtime
flag.

> - Why would we restrict referencing the flags in phase functions?
>   For example, I would consider something like the following in
>   pkg_postinst() a valid use case:
>
>       use foo || elog "For foo support, install package app-misc/foo"

I'm not really convinced by this. Once we add the runtime USE flag to
pull foo, I'd rather say we ought not to tell people to install packages
manually. But telling them that a particular flag controls something
should be fine... though it should be noted that we won't be able to
output another message afterwards.

>   Instead, I suggest that we simply say "runtime switchable flags must
>   not have any effect on the files installed by the ebuild".

Of course, your arguments are valid, so we can pretty much use
the simpler version in the PMS. Even then, most points listed verbosely
in GLEP would be implied, so we could do the checks.

> [1] https://wiki.gentoo.org/wiki/GLEP:62
> [2] https://forums.gentoo.org/viewtopic-p-4194219.html#4194219
> [3] https://wiki.gentoo.org/wiki/GLEP:62#Specification

-- 
Best regards,
Michał Górny