[gentoo-dev] REQUIRED_USE in EAPI 4

[Ulrich Mueller]

Hello all,

As you probably have noticed, the Council has frozen the feature set
for EAPI 4 in its November meeting [1], based on the current status of
implementation in portage. These features include the REQUIRED_USE
variable that will allow to specify constraints on USE flags possible
for an ebuild, as proposed by ferringb [2].

A first wording for the REQUIRED_USE specification in PMS is available
in bug 347353 [3]. As was pointed out in that bug, the current
treatment of violated USE flag constraints isn't optimal. Portage
basically would output "REQUIRED_USE violated", together with the
variable's value and the package name. Such a message might not be
very helpful for the user. And presumably there is no universal
algorithm that can output a reasonable suggestion based on USE and
REQUIRED_USE.

Since generally the ebuild maintainer will know best what should be
suggested to the user, a new function "pkg_required_use" has been
proposed by zmedico. It would be triggered only in the case that
REQUIRED_USE is not fulfilled, and it would output a message for the
user, similar to pkg_nofetch for fetch-restricted packages.

Comments?

Ulrich

[1] <http://www.gentoo.org/proj/en/council/meeting-logs/20101130.txt>
    <http://www.gentoo.org/proj/en/council/meeting-logs/20101130-summary.txt>
[2] <http://archives.gentoo.org/gentoo-dev/msg_b0e868626019f497eba47194c34e5421.xml>
[3] <http://bugs.gentoo.org/show_bug.cgi?id=347353>