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GLEP: 29 |
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Title: USE flag groups |
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Version: $Revision: 1.4 $ |
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Author: Ciaran McCreesh <ciaranm@gentoo.org> |
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Last-Modified: $Date: 2004/10/25 16:57:09 $ |
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Status: Draft |
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Type: Standards Track |
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Content-Type: text/x-rst |
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Created: 19-August-2004 |
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Post-Date: 21-August-2004, 18-October-2004, 25-October-2004, 24-July-2005 |
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|
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Status |
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====== |
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|
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Withdrawn by request of the author. |
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|
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Abstract |
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======== |
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|
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Currently, USE flags must be selected on a one-by-one basis, making it |
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time-consuming to set up make.conf appropriately for a machine's role. |
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|
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Motivation |
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========== |
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|
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Many packages have optional support for other packages (for example, the |
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Vim text editor can optionally support perl, python and ruby |
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interpreters). In Gentoo, these optional dependencies can be selected by |
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the user using USE flags. This allows a system appropriate for a given |
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environment to be built -- a server, for example, should not typically |
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have an X11 server or sound support, whereas both would be desirable on |
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most desktop systems. |
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|
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With several hundred USE flags available, deciding upon which USE flags to |
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enable and which to disable can take a long time. Although the default USE |
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flag settings are reasonable, they are clearly not appropriate for every |
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system. In addition, using "-*" to disable all default USE flags can be |
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risky as certain USE flags should not generally be turned off. This GLEP |
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proposes a mechanism for grouping USE flags to simplify selection and to |
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make USE="-*" less dangerous. |
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|
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Specification |
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============= |
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|
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Group Specification |
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------------------- |
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|
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A group shall consist of one or more tokens. Each token may be a USE flag, |
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a -USE flag, a reference to another group or a negative reference to |
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another group. |
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|
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These groups are defined in ``${PORTDIR}/profiles/use.groups``. It is |
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proposed that uppercase names only are used for groups to keep them |
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visually distinct from normal USE flags (almost all USE flags are |
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lowercase), although this should not been forced programmatically. The |
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file should be similar in format to the existing use.* files. In the |
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following, ``SOME_GROUP`` and ``OTHER_GROUP`` are group names, and |
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``flag1`` through ``flag5`` are USE flag names: |
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|
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:: |
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|
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SOME_GROUP flag1 flag2 flag3 |
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OTHER_GROUP flag2 flag4 |
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|
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Groups may recursively include other groups. For consistency with GLEP 23 |
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[1]_, it is proposed that group names have their name prefixed with an |
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'at' symbol (@): |
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|
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:: |
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|
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GROUP1 flag1 |
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GROUP2 flag2 flag3 @GROUP1 |
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GROUP3 flag4 |
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GROUP4 @GROUP2 @GROUP3 flag5 |
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|
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The same flag may end up being in a particular group more than once: |
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|
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:: |
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|
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GROUP1 flag1 flag2 |
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GROUP2 flag2 flag3 |
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GROUP3 @GROUP1 @GROUP2 flag3 flag4 |
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|
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As with similar files, comments may be included. Lines which begin with a |
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hash symbol (#) are comments. |
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|
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:: |
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|
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# This is a comment |
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FOO bar baz fnord |
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|
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Users may create their own groups using ``/etc/portage/use.groups``. This |
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file overrides the profile settings in the case of duplicates. |
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|
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It should be legal for groups to specify -use flags, although for reasons |
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discussed below this feature should not generally be used. The syntax is |
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the same: |
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|
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:: |
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|
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# This group contains two negative flags |
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GROUP1 flag1 -flag2 -flag3 flag4 |
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|
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Groups may *not* contain circular group references. The following example |
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is illegal: |
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|
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:: |
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|
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# Illegal circular references |
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GROUP1 @GROUP2 foo |
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GROUP2 @GROUP1 bar |
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|
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Group Descriptions |
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------------------ |
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|
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Groups shall have a textual description associated with them in the same |
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way as USE flags. The file ``${PORTDIR}/profiles/use.groups.desc`` |
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contains these: |
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|
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:: |
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|
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# This is a comment |
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DESKTOP Flags which are appropriate for most desktop systems |
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RECOMMENDED Flags which should be enabled on almost all systems |
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|
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|
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Using Groups |
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------------ |
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|
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Groups may be used in ``/etc/make.conf``, ``/etc/portage/package.use`` and |
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other places where USE flags are normally specified. They may *not* be |
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used inside ``IUSE`. As before, the @ symbol is used to indicate that a |
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group is being referenced. For example, a ``make.conf`` for a KDE desktop |
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system might resemble: |
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|
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:: |
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|
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USE="@DESKTOP @KDE perl alsa dvd" |
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|
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Groups may be preceded by a -sign to invert their contents (that is, all |
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'enable' use flags become -flags, and all -flags become enable flags). Be |
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warned that this feature can cause confusion (see below). Example usage: |
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|
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:: |
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|
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# We have the following groups defined... |
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GROUP1 foo bar |
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GROUP2 -bar baz -fnord |
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GROUP3 @GROUP1 -@GROUP2 -bar foo |
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GROUP4 -foo -bar |
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|
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# And the following... |
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USE="-@GROUP3 @GROUP4 bar" |
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|
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# which resolves to... |
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USE="-@GROUP1 @GROUP2 bar -foo -foo -bar bar" |
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USE="-foo -bar bar -baz fnord bar -foo -foo -bar bar" |
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USE="-baz fnord -foo bar" |
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|
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|
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Issues with -flags and -@GROUPS |
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------------------------------- |
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|
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Earlier drafts of this GLEP did not allow -use flags or -@GROUPS. However, |
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because of feedback along the lines of "we shouldn't disallow features |
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just because some users won't understand them" (for example, [3]_), these |
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are now allowed but discouraged. |
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|
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The problems are best illustrated by example. Say we have the following |
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groups defined: |
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|
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:: |
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|
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KDE X kde qt |
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GNOME X gtk gtk2 gnome |
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|
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A user who wants a KDE desktop but no GNOME may do the following: |
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|
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:: |
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|
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USE="@KDE -@GNOME" |
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|
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However, this will not give the desired effect -- the ``X`` USE flag will |
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end up being disabled. |
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|
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Similarly, -use flags could cause a lot of confusion if misused. If, for |
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example, the KDE group turned off GNOME things and the GNOME group turned |
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off KDE things: |
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|
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:: |
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|
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KDE X kde qt -gtk -gnome |
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GNOME X gtk gtk2 gnome -kde -qt |
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|
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And a user wished to use both KDE and GNOME on a system, and so had USE |
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flags as follows: |
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|
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:: |
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|
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USE="@KDE @GNOME" |
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|
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They would end up with: |
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|
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:: |
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USE="X kde qt -gtk -gnome X gtk gtk2 gnome -kde -qt" |
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|
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Which simplifies: |
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|
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:: |
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|
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USE="X gtk gtk2 gnome -kde -qt" |
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|
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This is clearly not the desired effect. |
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|
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Adding New Groups |
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----------------- |
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|
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The actual groups to be created is beyond the scope of this GLEP, and any |
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group names contained herein should be treated as examples only. Creation |
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of new groups and changing a group's flags should be discussed on the |
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gentoo-dev mailing list as per existing policy for new global USE flags. |
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|
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In particular, any changes involving -flags *must* be thoroughly discussed |
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before implementation. |
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|
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Rationale |
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========= |
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|
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USE groups will simplify selecting an appropriate set of USE flags for a |
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system. |
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|
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Reference Implementation |
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======================== |
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|
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TODO |
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|
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Backwards Compatibility |
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======================= |
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|
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The user will not need to make any changes to keep their current setup. |
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Users who are not running a portage version which supports groups can |
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carry on using current syntax with no side-effects. |
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|
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Some tools which work with make.conf and / or USE flags (for example, |
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``ufed``) will need to be updated to understand the new group syntax. |
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|
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There is currently a dynamic list of USE flags available on the Gentoo |
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website [2]_. For consistency, a similar list will be needed for USE |
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groups. |
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|
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References |
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========== |
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|
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.. [1] GLEP 23: Portage handling of ACCEPT_LICENSE |
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(http://www.gentoo.org/proj/en/glep/glep-0023.html) |
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.. [2] http://www.gentoo.org/dyn/use-index.xml |
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.. [3] GLEP 29 discussion on the gentoo-dev mailing list |
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(http://marc.theaimsgroup.com/?l=gentoo-dev&m=109813990013812) |
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|
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Copyright |
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========= |
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|
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This document has been placed in the public domain. |
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|
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vim: set tw=74 : |
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