Versioned USE flags¶
If a need arises to create new USE flags responsible for switching
between multiple versions of a specific dependency, it is recommended
that flat, explicitly versioned flags are used (e.g.
The hierarchical form used e.g. by GTK+ (
gtk meaning 2-or-3,
gtk3 to switch between both)
Any future set of USE flags introduced in this way needs to be discussed with the QA team before introduction.
This policy has historically been defined as an generalization of the QA policy on gtk/gtk2/gtk3 flags. The latter policy has been removed since.
Whenever a package offers an optional GUI support, the
gui flag must
be used to control that support rather than historically used
or toolkit flags. Toolkit flags can still be used to choose between
multiple available GUIs, or when the toolkit is used in a more
specialized way than for GUI (e.g. to control installing widgets).
Rationale: the historical use of toolkit flags to control building GUIs made it very hard for users to express the simple wish of ‘I want any GUI’. Installing various packages made it necessary to either adjust flags per package (manually discovering which flags are necessary to obtain the GUI) or enabling multiple toolkits globally which afterwards caused issues with packages supporting a choice between multiple GUIs.
Underscores in USE flag names¶
Underscores are reserved for USE_EXPAND flags, and must not be used within names of newly-defined regular flags. Existing uses are considered technically valid, and phasing them out has low priority.
Flags that attempt to resemble USE_EXPAND should be either converted into proper (global) USE_EXPAND, or made into shorter (unprefixed) local flags. In other flags, replacing underscore with hyphen is recommended.
Rationale: a few packages in Gentoo attempted to imitate USE_EXPAND via local USE flags. This has no clear advantage, may be confusing to end users who assume that they will work like USE_EXPAND and in the end unnecessarily lengthens flag names or even causes unnecessary mismatches between global flags and local flags.
Extending the rule to all flags containing underscores aims to make distinguishing USE_EXPAND and regular flags easier. It also improves consistency between flag names that historically used hyphens or underscores depending on developer’s personal preference.