La language de portage

Il est parfois difficile de décrypter le language de portage! Je voulais installer le designer de qt :

 # emerge -va designer

 * IMPORTANT: 24 news items need reading for repository 'gentoo'.
 * Use eselect news read to view new items.


 * IMPORTANT: 3 config files in '/etc/portage' need updating.
 * See the CONFIGURATION FILES section of the emerge
 * man page to learn how to update config files.

These are the packages that would be merged, in order:

Calculating dependencies... done!

!!! The ebuild selected to satisfy ">=dev-qt/qtgui-5.4.2:5" has unmet requirements.
- dev-qt/qtgui-5.4.2-r1::gentoo USE="dbus gif harfbuzz jpeg png udev -accessibility -debug -egl -eglfs -evdev -gles2 -gtkstyle -ibus -test -xcb" ABI_X86="64"

  The following REQUIRED_USE flag constraints are unsatisfied:
    any-of ( eglfs xcb )

  The above constraints are a subset of the following complete expression:
    any-of ( eglfs xcb ) accessibility? ( dbus xcb ) egl? ( evdev ) eglfs? ( egl ) ibus? ( dbus )

Comment comprendre ce message? La ligne

  The following REQUIRED_USE flag constraints are unsatisfied:
    any-of ( eglfs xcb )

nous dis que eglfs et/ou xcb doit être activer. En guise de test, je peux lancer la commande :

 # USE="xcb" emerge -va designer

 * IMPORTANT: 24 news items need reading for repository 'gentoo'.
 * Use eselect news read to view new items.


 * IMPORTANT: 3 config files in '/etc/portage' need updating.
 * See the CONFIGURATION FILES section of the emerge
 * man page to learn how to update config files.

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N     ] x11-libs/libxkbcommon-0.5.0::gentoo  USE="X -doc -static-libs {-test}" ABI_X86="(64) -32 (-x32)" 602 KiB
[ebuild   R    ] dev-libs/libpcre-8.38:3::gentoo  USE="bzip2 cxx jit pcre16* readline recursion-limit (unicode) zlib -libedit -pcre32 -static-libs" ABI_X86="(64) -32 (-x32)" 0 KiB
[ebuild  NS    ] dev-qt/qtcore-5.4.2:5::gentoo [4.8.6-r2:4::gentoo] USE="-debug -icu -systemd {-test}" 45268 KiB
[ebuild  N     ] dev-qt/qtnetwork-5.4.2:5::gentoo  USE="bindist ssl -connman -debug -networkmanager {-test}" 0 KiB
[ebuild  N     ] dev-qt/qtxml-5.4.2:5::gentoo  USE="-debug {-test}" 0 KiB
[ebuild  NS    ] dev-qt/qtdbus-5.4.2:5::gentoo [4.8.6-r1:4::gentoo] USE="-debug {-test}" 0 KiB
[ebuild  NS    ] dev-qt/qtgui-5.4.2-r1:5::gentoo [4.8.6-r4:4::gentoo] USE="dbus gif harfbuzz jpeg png udev xcb -accessibility -debug -egl -eglfs -evdev -gles2 -gtkstyle -ibus {-test}" 0 KiB
[ebuild  N     ] dev-qt/qtwidgets-5.4.2:5::gentoo  USE="png xcb -debug -gles2 -gtkstyle {-test}" 0 KiB
[ebuild  N     ] dev-qt/qtprintsupport-5.4.2:5::gentoo  USE="cups -debug -gles2 {-test}" 0 KiB
[ebuild  N     ] dev-qt/designer-5.4.2:5::gentoo  USE="-debug -declarative {-test} -webkit" 9115 KiB

Total: 10 packages (6 new, 3 in new slots, 1 reinstall), Size of downloads: 54984 KiB

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by dev-qt/qtcore-5.4.2::gentoo
# required by dev-qt/designer-5.4.2::gentoo
# required by designer (argument)
>=dev-libs/libpcre-8.38 pcre16

Donc, tout peut fonctionner avec xcb d'activer. Je dois donc rendre cette modification permanente. J'ai deux choix, soit ajouter l'option dans /etc/portage/package.use pour activer cette fonctionnalité à ce package seulement ou l'ajouter dans /etc/portage/make.conf pour activer cette fonctionnalité globalement. J'ai choisi la première option et j'ajoute la ligne demander à la fin de la commande emerge. J'ajoute donc dans /etc/portage/package.use :

>=dev-qt/qtgui-5.4.2  xcb

# required by dev-qt/qtcore-5.4.2::gentoo
# required by dev-qt/designer-5.4.2::gentoo
# required by designer (argument)
>=dev-libs/libpcre-8.38 pcre16