[gentoo-pms] Runtime-switchable USE flags

[Ulrich Mueller]

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.

- 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.

- 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"

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

Ulrich


[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