en/glep/glep-0029.txt

GLEP: 29
Title: USE flag groups
Version: $Revision: 1.4 $
Author: Ciaran McCreesh <ciaranm@gentoo.org>
Last-Modified: $Date: 2004/10/25 16:57:09 $
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 19-August-2004
Post-Date: 21-August-2004, 18-October-2004, 25-October-2004, 24-July-2005

Status
======

Withdrawn by request of the author.

Abstract
========

Currently, USE flags must be selected on a one-by-one basis, making it
time-consuming to set up make.conf appropriately for a machine's role.

Motivation
==========

Many packages have optional support for other packages (for example, the
Vim text editor can optionally support perl, python and ruby
interpreters). In Gentoo, these optional dependencies can be selected by
the user using USE flags. This allows a system appropriate for a given
environment to be built -- a server, for example, should not typically
have an X11 server or sound support, whereas both would be desirable on
most desktop systems.

With several hundred USE flags available, deciding upon which USE flags to
enable and which to disable can take a long time. Although the default USE
flag settings are reasonable, they are clearly not appropriate for every
system. In addition, using "-*" to disable all default USE flags can be
risky as certain USE flags should not generally be turned off.  This GLEP
proposes a mechanism for grouping USE flags to simplify selection and to
make USE="-*" less dangerous.

Specification
=============

Group Specification
-------------------

A group shall consist of one or more tokens. Each token may be a USE flag,
a -USE flag, a reference to another group or a negative reference to
another group.

These groups are defined in ``${PORTDIR}/profiles/use.groups``. It is
proposed that uppercase names only are used for groups to keep them
visually distinct from normal USE flags (almost all USE flags are
lowercase), although this should not been forced programmatically. The
file should be similar in format to the existing use.* files. In the
following, ``SOME_GROUP`` and ``OTHER_GROUP`` are group names, and
``flag1`` through ``flag5`` are USE flag names:

::

        SOME_GROUP flag1 flag2 flag3
        OTHER_GROUP flag2 flag4

Groups may recursively include other groups. For consistency with GLEP 23
[1]_, it is proposed that group names have their name prefixed with an
'at' symbol (@):

::

        GROUP1 flag1
        GROUP2 flag2 flag3 @GROUP1
        GROUP3 flag4
        GROUP4 @GROUP2 @GROUP3 flag5

The same flag may end up being in a particular group more than once:

::

        GROUP1 flag1 flag2
        GROUP2 flag2 flag3
        GROUP3 @GROUP1 @GROUP2 flag3 flag4

As with similar files, comments may be included. Lines which begin with a
hash symbol (#) are comments.

::

        # This is a comment
        FOO bar baz fnord

Users may create their own groups using ``/etc/portage/use.groups``. This
file overrides the profile settings in the case of duplicates.

It should be legal for groups to specify -use flags, although for reasons
discussed below this feature should not generally be used. The syntax is
the same:

::

        # This group contains two negative flags
        GROUP1 flag1 -flag2 -flag3 flag4

Groups may *not* contain circular group references. The following example
is illegal:

::

        # Illegal circular references
        GROUP1 @GROUP2 foo
        GROUP2 @GROUP1 bar

Group Descriptions
------------------

Groups shall have a textual description associated with them in the same
way as USE flags. The file ``${PORTDIR}/profiles/use.groups.desc``
contains these:

::

        # This is a comment
        DESKTOP Flags which are appropriate for most desktop systems
        RECOMMENDED Flags which should be enabled on almost all systems


Using Groups
------------

Groups may be used in ``/etc/make.conf``, ``/etc/portage/package.use`` and
other places where USE flags are normally specified. They may *not* be
used inside ``IUSE`. As before, the @ symbol is used to indicate that a
group is being referenced. For example, a ``make.conf`` for a KDE desktop
system might resemble:

::

        USE="@DESKTOP @KDE perl alsa dvd"

Groups may be preceded by a -sign to invert their contents (that is, all
'enable' use flags become -flags, and all -flags become enable flags). Be
warned that this feature can cause confusion (see below). Example usage:

::

        # We have the following groups defined...
        GROUP1 foo bar
        GROUP2 -bar baz -fnord
        GROUP3 @GROUP1 -@GROUP2 -bar foo
        GROUP4 -foo -bar

        # And the following...
        USE="-@GROUP3 @GROUP4 bar"

        # which resolves to...
        USE="-@GROUP1 @GROUP2 bar -foo -foo -bar bar"
        USE="-foo -bar bar -baz fnord bar -foo -foo -bar bar"
        USE="-baz fnord -foo bar"


Issues with -flags and -@GROUPS
-------------------------------

Earlier drafts of this GLEP did not allow -use flags or -@GROUPS. However,
because of feedback along the lines of "we shouldn't disallow features
just because some users won't understand them" (for example, [3]_), these
are now allowed but discouraged.

The problems are best illustrated by example. Say we have the following
groups defined:

::

        KDE X kde qt
        GNOME X gtk gtk2 gnome

A user who wants a KDE desktop but no GNOME may do the following:

::

        USE="@KDE -@GNOME"

However, this will not give the desired effect -- the ``X`` USE flag will
end up being disabled.

Similarly, -use flags could cause a lot of confusion if misused. If, for
example, the KDE group turned off GNOME things and the GNOME group turned
off KDE things:

::

        KDE X kde qt -gtk -gnome
        GNOME X gtk gtk2 gnome -kde -qt

And a user wished to use both KDE and GNOME on a system, and so had USE
flags as follows:

::

        USE="@KDE @GNOME"

They would end up with:

::

        USE="X kde qt -gtk -gnome X gtk gtk2 gnome -kde -qt"

Which simplifies:

::

        USE="X gtk gtk2 gnome -kde -qt"

This is clearly not the desired effect.

Adding New Groups
-----------------

The actual groups to be created is beyond the scope of this GLEP, and any
group names contained herein should be treated as examples only. Creation
of new groups and changing a group's flags should be discussed on the
gentoo-dev mailing list as per existing policy for new global USE flags.

In particular, any changes involving -flags *must* be thoroughly discussed
before implementation.

Rationale
=========

USE groups will simplify selecting an appropriate set of USE flags for a
system.

Reference Implementation
========================

TODO

Backwards Compatibility
=======================

The user will not need to make any changes to keep their current setup.
Users who are not running a portage version which supports groups can
carry on using current syntax with no side-effects.

Some tools which work with make.conf and / or USE flags (for example,
``ufed``) will need to be updated to understand the new group syntax.

There is currently a dynamic list of USE flags available on the Gentoo
website [2]_. For consistency, a similar list will be needed for USE
groups.

References
==========

.. [1] GLEP 23: Portage handling of ACCEPT_LICENSE
       (http://www.gentoo.org/proj/en/glep/glep-0023.html)
.. [2] http://www.gentoo.org/dyn/use-index.xml
.. [3] GLEP 29 discussion on the gentoo-dev mailing list
       (http://marc.theaimsgroup.com/?l=gentoo-dev&m=109813990013812)

Copyright
=========

This document has been placed in the public domain.

 vim: set tw=74 :
1	GLEP: 29
2	Title: USE flag groups
3	Version: $Revision: 1.4 $
4	Author: Ciaran McCreesh <ciaranm@gentoo.org>
5	Last-Modified: $Date: 2004/10/25 16:57:09 $
6	Status: Draft
7	Type: Standards Track
8	Content-Type: text/x-rst
9	Created: 19-August-2004
10	Post-Date: 21-August-2004, 18-October-2004, 25-October-2004, 24-July-2005
11
12	Status
13	======
14
15	Withdrawn by request of the author.
16
17	Abstract
18	========
19
20	Currently, USE flags must be selected on a one-by-one basis, making it
21	time-consuming to set up make.conf appropriately for a machine's role.
22
23	Motivation
24	==========
25
26	Many packages have optional support for other packages (for example, the
27	Vim text editor can optionally support perl, python and ruby
28	interpreters). In Gentoo, these optional dependencies can be selected by
29	the user using USE flags. This allows a system appropriate for a given
30	environment to be built -- a server, for example, should not typically
31	have an X11 server or sound support, whereas both would be desirable on
32	most desktop systems.
33
34	With several hundred USE flags available, deciding upon which USE flags to
35	enable and which to disable can take a long time. Although the default USE
36	flag settings are reasonable, they are clearly not appropriate for every
37	system. In addition, using "-*" to disable all default USE flags can be
38	risky as certain USE flags should not generally be turned off. This GLEP
39	proposes a mechanism for grouping USE flags to simplify selection and to
40	make USE="-*" less dangerous.
41
42	Specification
43	=============
44
45	Group Specification
46	-------------------
47
48	A group shall consist of one or more tokens. Each token may be a USE flag,
49	a -USE flag, a reference to another group or a negative reference to
50	another group.
51
52	These groups are defined in ``${PORTDIR}/profiles/use.groups``. It is
53	proposed that uppercase names only are used for groups to keep them
54	visually distinct from normal USE flags (almost all USE flags are
55	lowercase), although this should not been forced programmatically. The
56	file should be similar in format to the existing use.* files. In the
57	following, ``SOME_GROUP`` and ``OTHER_GROUP`` are group names, and
58	``flag1`` through ``flag5`` are USE flag names:
59
60	::
61
62	SOME_GROUP flag1 flag2 flag3
63	OTHER_GROUP flag2 flag4
64
65	Groups may recursively include other groups. For consistency with GLEP 23
66	[1]_, it is proposed that group names have their name prefixed with an
67	'at' symbol (@):
68
69	::
70
71	GROUP1 flag1
72	GROUP2 flag2 flag3 @GROUP1
73	GROUP3 flag4
74	GROUP4 @GROUP2 @GROUP3 flag5
75
76	The same flag may end up being in a particular group more than once:
77
78	::
79
80	GROUP1 flag1 flag2
81	GROUP2 flag2 flag3
82	GROUP3 @GROUP1 @GROUP2 flag3 flag4
83
84	As with similar files, comments may be included. Lines which begin with a
85	hash symbol (#) are comments.
86
87	::
88
89	# This is a comment
90	FOO bar baz fnord
91
92	Users may create their own groups using ``/etc/portage/use.groups``. This
93	file overrides the profile settings in the case of duplicates.
94
95	It should be legal for groups to specify -use flags, although for reasons
96	discussed below this feature should not generally be used. The syntax is
97	the same:
98
99	::
100
101	# This group contains two negative flags
102	GROUP1 flag1 -flag2 -flag3 flag4
103
104	Groups may not contain circular group references. The following example
105	is illegal:
106
107	::
108
109	# Illegal circular references
110	GROUP1 @GROUP2 foo
111	GROUP2 @GROUP1 bar
112
113	Group Descriptions
114	------------------
115
116	Groups shall have a textual description associated with them in the same
117	way as USE flags. The file ``${PORTDIR}/profiles/use.groups.desc``
118	contains these:
119
120	::
121
122	# This is a comment
123	DESKTOP Flags which are appropriate for most desktop systems
124	RECOMMENDED Flags which should be enabled on almost all systems
125
126
127	Using Groups
128	------------
129
130	Groups may be used in ``/etc/make.conf``, ``/etc/portage/package.use`` and
131	other places where USE flags are normally specified. They may not be
132	used inside ``IUSE`. As before, the @ symbol is used to indicate that a
133	group is being referenced. For example, a ``make.conf`` for a KDE desktop
134	system might resemble:
135
136	::
137
138	USE="@DESKTOP @KDE perl alsa dvd"
139
140	Groups may be preceded by a -sign to invert their contents (that is, all
141	'enable' use flags become -flags, and all -flags become enable flags). Be
142	warned that this feature can cause confusion (see below). Example usage:
143
144	::
145
146	# We have the following groups defined...
147	GROUP1 foo bar
148	GROUP2 -bar baz -fnord
149	GROUP3 @GROUP1 -@GROUP2 -bar foo
150	GROUP4 -foo -bar
151
152	# And the following...
153	USE="-@GROUP3 @GROUP4 bar"
154
155	# which resolves to...
156	USE="-@GROUP1 @GROUP2 bar -foo -foo -bar bar"
157	USE="-foo -bar bar -baz fnord bar -foo -foo -bar bar"
158	USE="-baz fnord -foo bar"
159
160
161	Issues with -flags and -@GROUPS
162	-------------------------------
163
164	Earlier drafts of this GLEP did not allow -use flags or -@GROUPS. However,
165	because of feedback along the lines of "we shouldn't disallow features
166	just because some users won't understand them" (for example, [3]_), these
167	are now allowed but discouraged.
168
169	The problems are best illustrated by example. Say we have the following
170	groups defined:
171
172	::
173
174	KDE X kde qt
175	GNOME X gtk gtk2 gnome
176
177	A user who wants a KDE desktop but no GNOME may do the following:
178
179	::
180
181	USE="@KDE -@GNOME"
182
183	However, this will not give the desired effect -- the ``X`` USE flag will
184	end up being disabled.
185
186	Similarly, -use flags could cause a lot of confusion if misused. If, for
187	example, the KDE group turned off GNOME things and the GNOME group turned
188	off KDE things:
189
190	::
191
192	KDE X kde qt -gtk -gnome
193	GNOME X gtk gtk2 gnome -kde -qt
194
195	And a user wished to use both KDE and GNOME on a system, and so had USE
196	flags as follows:
197
198	::
199
200	USE="@KDE @GNOME"
201
202	They would end up with:
203
204	::
205
206	USE="X kde qt -gtk -gnome X gtk gtk2 gnome -kde -qt"
207
208	Which simplifies:
209
210	::
211
212	USE="X gtk gtk2 gnome -kde -qt"
213
214	This is clearly not the desired effect.
215
216	Adding New Groups
217	-----------------
218
219	The actual groups to be created is beyond the scope of this GLEP, and any
220	group names contained herein should be treated as examples only. Creation
221	of new groups and changing a group's flags should be discussed on the
222	gentoo-dev mailing list as per existing policy for new global USE flags.
223
224	In particular, any changes involving -flags must be thoroughly discussed
225	before implementation.
226
227	Rationale
228	=========
229
230	USE groups will simplify selecting an appropriate set of USE flags for a
231	system.
232
233	Reference Implementation
234	========================
235
236	TODO
237
238	Backwards Compatibility
239	=======================
240
241	The user will not need to make any changes to keep their current setup.
242	Users who are not running a portage version which supports groups can
243	carry on using current syntax with no side-effects.
244
245	Some tools which work with make.conf and / or USE flags (for example,
246	``ufed``) will need to be updated to understand the new group syntax.
247
248	There is currently a dynamic list of USE flags available on the Gentoo
249	website [2]_. For consistency, a similar list will be needed for USE
250	groups.
251
252	References
253	==========
254
255	.. [1] GLEP 23: Portage handling of ACCEPT_LICENSE
256	(http://www.gentoo.org/proj/en/glep/glep-0023.html)
257	.. [2] http://www.gentoo.org/dyn/use-index.xml
258	.. [3] GLEP 29 discussion on the gentoo-dev mailing list
259	(http://marc.theaimsgroup.com/?l=gentoo-dev&m=109813990013812)
260
261	Copyright
262	=========
263
264	This document has been placed in the public domain.
265
266	vim: set tw=74 :