en/glep/glep-0021.txt

GLEP: 21
Title: User-defined Package Sets
Version: $Revision: 1.5 $ 
Last-Modified: $Date: 2007/10/21 11:42:57 $
Author: Tal Peer <coredumb@gentoo.org>,
        Alec Warner <antarus@gentoo.org>
Status: Final
Type: Standards Track
Discussed-To: gentoo-portage-dev@lists.gentoo.org
Content-Type: text/x-rst
Created: 22-Feb-2004
Post-History: 6-Mar-2004, 3-Sep-2006

Status
======

Abandoned. Package set support has been added in portage-2.2, but it 
doesn't match the description in this document in many cases, and the
document has several major gaps regarding the behavior and restrictions 
of package sets.

Abstract
========

In Portage, package sets (formerly known as 'classes' or 'targets')
are mere groups of packages, grouped together to allow easier updating
and handling of them. Currently it is impossible to define sets further
than the two default ones: "system" and "world".

Motivation
==========

Over the months, quite a few requests for user-defined sets were
made by users and developers, either by posting bugs, messages to
mailing lists or on IRC. Usually the response is that this is an
awesome idea, but no one ever took the time to actually define it
properly and implement it.

This document offers a specification for the implementation of
user-defined sets using configuration files similar to the current
world/system sets use.

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

The proposed implementation uses a one file per set approach, meaning
each package set is defined in a single file. All set definition files
will reside in a directory ``/etc/portage/sets/`` and each set's name
will be its file name. Therefore, if one defines a set in
/etc/portage/sets/foo-set, the set name will be 'foo-set'. Usual
package naming rules [#NAME-RULES]_ also apply to sets.

As it is impossible to create two or more files with identical names
in the same directory, a theoretic conflict between two different sets
sharing the same name is impossible. However, users may define a
package set whose name conflicts with one more or packages (for ambiguity
resolution, see below).

Syntax for the package list file is the same as the world file syntax,
as described in the Portage manpage [#PORTAGE-MANPAGE]_, with one
addition: sets may not be 'inherited' by other sets, only packages may
be listed. There is no limitation to the number of packages in a set
or to the number of sets a package may belong to.

Using User-defined Sets With Emerge
--------------------------------------

The user-defined sets will be available either directly or using
the --package-set option, As in::

        # Basically the same:
        emerge foo-set
        emerge --package-set foo-set

The --package-set option is introduced to bypass ambiguities, as
illustrated in the next example::

        emerge foo                # Where foo is both a set and a one or more
                                  # existing packages. This will cause emerge to show
                                  # the ambiguity, ask us to be more
                                  # specific, and stop.
        
        emerge --package-set foo  # So we specify that what we actually
                                  # meant was the package set.

        emerge cat-bar/foo        # Or we specify the exact package name.

When running emerge with the --pretend option, sets will be
expanded to the packages they are comprised off in the output, as with
the current system-defined sets.

Only one set may be passed to portage at time, and sets can not
be mixed with ordinary packages. Thus, the following snippets are
all invalid and will result in an error  (assuming ``foo-set`` and 
``bar-set`` are defined as sets)::

        emerge foo-set glibc
        emerge bar-set system
        emerge world foo-set gcc

Compatibility With Other Portage Features
-----------------------------------------

* Dependencies:
  Package sets (both system-defined and user-defined) may not be
  depended on by ordinary packages and eclasses.
    
* package.mask:
  Masking a package set through the ``package.mask`` file is forbidden.
  In order to 'mask' a package set, one should move it away from the
  sets directory.

* package.use:
  USE flags may not be defined for sets in the ``package.use`` file.

Implementation
==============

The implementation of the package sets concept in Portage should be
mostly done in portage.py, and only the interface parts should be
added to emerge itself, to keep the separation between interface and
logic.

The amount of work needed for implementation is not trivial, but not
huge either.

Rationale
=========

The one file per set approach makes it easy to list the sets which are
defined on a system by just listing the ``/etc/portage/sets``
directory contents. Additionally, it makes the set lookup process more
efficient as it only requires to check if a file exists.

I chose the --package-set option over the --set option for explicitly
telling portage to emerge a set mostly because --set implies setting
an environment variable, or such.

Allowing sets' USE flags to be manipulated through the ``package.use``
file would have done more harm than good, for several reasons:

- If a USE flag is turned on (i.e. 'foo') for a set and the same USE
  flag is turned off (i.e. '-foo'), for a package which is part of
  the set, it is unclear which setting should take precedence.

- Similarly, if a USE flag is turned on for a set and the same USE flag
  is turned off for a set that is a subset of the original set, it is
  unclear which setting should take precedence.

- If a USE flag is defined (either off or on) for a set and a package
  that belongs in the set is to be emerged, it is unclear whether the
  USE flag should be defined when emerging the package in question.

Therefore, I have decided it would be better to disallow setting USE
flags for sets.

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

Backwards compatibility with the current situation, in which only two
system-defined sets exist can be kept in one of two ways:

1. Leaving the situation as is - the 'world' and 'system' sets are
   hard-coded in Portage.
2. Distributing default 'system' and 'world' files under the
   ``/etc/portage/sets/`` directory.

Other than that, there are no other backwards compatibility concerns
involved.

References
==========

.. [#NAME-RULES] Gentoo Linux Development Policy - Ebuild Policy
   (http://www.gentoo.org/doc/en/policy.xml#doc_chap3)
   
.. [#PORTAGE-MANPAGE]
   http://www.gentoo.org/cgi-bin/viewcvs.cgi/portage/man/portage.5?root=gentoo-src

Copyright
=========

This document has been placed in the public domain.

1	GLEP: 21
2	Title: User-defined Package Sets
3	Version: $Revision: 1.5 $
4	Last-Modified: $Date: 2007/10/21 11:42:57 $
5	Author: Tal Peer <coredumb@gentoo.org>,
6	Alec Warner <antarus@gentoo.org>
7	Status: Final
8	Type: Standards Track
9	Discussed-To: gentoo-portage-dev@lists.gentoo.org
10	Content-Type: text/x-rst
11	Created: 22-Feb-2004
12	Post-History: 6-Mar-2004, 3-Sep-2006
13
14	Status
15	======
16
17	Abandoned. Package set support has been added in portage-2.2, but it
18	doesn't match the description in this document in many cases, and the
19	document has several major gaps regarding the behavior and restrictions
20	of package sets.
21
22	Abstract
23	========
24
25	In Portage, package sets (formerly known as 'classes' or 'targets')
26	are mere groups of packages, grouped together to allow easier updating
27	and handling of them. Currently it is impossible to define sets further
28	than the two default ones: "system" and "world".
29
30	Motivation
31	==========
32
33	Over the months, quite a few requests for user-defined sets were
34	made by users and developers, either by posting bugs, messages to
35	mailing lists or on IRC. Usually the response is that this is an
36	awesome idea, but no one ever took the time to actually define it
37	properly and implement it.
38
39	This document offers a specification for the implementation of
40	user-defined sets using configuration files similar to the current
41	world/system sets use.
42
43	Specification
44	=============
45
46	The proposed implementation uses a one file per set approach, meaning
47	each package set is defined in a single file. All set definition files
48	will reside in a directory ``/etc/portage/sets/`` and each set's name
49	will be its file name. Therefore, if one defines a set in
50	/etc/portage/sets/foo-set, the set name will be 'foo-set'. Usual
51	package naming rules [#NAME-RULES]_ also apply to sets.
52
53	As it is impossible to create two or more files with identical names
54	in the same directory, a theoretic conflict between two different sets
55	sharing the same name is impossible. However, users may define a
56	package set whose name conflicts with one more or packages (for ambiguity
57	resolution, see below).
58
59	Syntax for the package list file is the same as the world file syntax,
60	as described in the Portage manpage [#PORTAGE-MANPAGE]_, with one
61	addition: sets may not be 'inherited' by other sets, only packages may
62	be listed. There is no limitation to the number of packages in a set
63	or to the number of sets a package may belong to.
64
65	Using User-defined Sets With Emerge
66	--------------------------------------
67
68	The user-defined sets will be available either directly or using
69	the --package-set option, As in::
70
71	# Basically the same:
72	emerge foo-set
73	emerge --package-set foo-set
74
75	The --package-set option is introduced to bypass ambiguities, as
76	illustrated in the next example::
77
78	emerge foo # Where foo is both a set and a one or more
79	# existing packages. This will cause emerge to show
80	# the ambiguity, ask us to be more
81	# specific, and stop.
82
83	emerge --package-set foo # So we specify that what we actually
84	# meant was the package set.
85
86	emerge cat-bar/foo # Or we specify the exact package name.
87
88	When running emerge with the --pretend option, sets will be
89	expanded to the packages they are comprised off in the output, as with
90	the current system-defined sets.
91
92	Only one set may be passed to portage at time, and sets can not
93	be mixed with ordinary packages. Thus, the following snippets are
94	all invalid and will result in an error (assuming ``foo-set`` and
95	``bar-set`` are defined as sets)::
96
97	emerge foo-set glibc
98	emerge bar-set system
99	emerge world foo-set gcc
100
101	Compatibility With Other Portage Features
102	-----------------------------------------
103
104	* Dependencies:
105	Package sets (both system-defined and user-defined) may not be
106	depended on by ordinary packages and eclasses.
107
108	* package.mask:
109	Masking a package set through the ``package.mask`` file is forbidden.
110	In order to 'mask' a package set, one should move it away from the
111	sets directory.
112
113	* package.use:
114	USE flags may not be defined for sets in the ``package.use`` file.
115
116	Implementation
117	==============
118
119	The implementation of the package sets concept in Portage should be
120	mostly done in portage.py, and only the interface parts should be
121	added to emerge itself, to keep the separation between interface and
122	logic.
123
124	The amount of work needed for implementation is not trivial, but not
125	huge either.
126
127	Rationale
128	=========
129
130	The one file per set approach makes it easy to list the sets which are
131	defined on a system by just listing the ``/etc/portage/sets``
132	directory contents. Additionally, it makes the set lookup process more
133	efficient as it only requires to check if a file exists.
134
135	I chose the --package-set option over the --set option for explicitly
136	telling portage to emerge a set mostly because --set implies setting
137	an environment variable, or such.
138
139	Allowing sets' USE flags to be manipulated through the ``package.use``
140	file would have done more harm than good, for several reasons:
141
142	- If a USE flag is turned on (i.e. 'foo') for a set and the same USE
143	flag is turned off (i.e. '-foo'), for a package which is part of
144	the set, it is unclear which setting should take precedence.
145
146	- Similarly, if a USE flag is turned on for a set and the same USE flag
147	is turned off for a set that is a subset of the original set, it is
148	unclear which setting should take precedence.
149
150	- If a USE flag is defined (either off or on) for a set and a package
151	that belongs in the set is to be emerged, it is unclear whether the
152	USE flag should be defined when emerging the package in question.
153
154	Therefore, I have decided it would be better to disallow setting USE
155	flags for sets.
156
157	Backwards Compatibility
158	=======================
159
160	Backwards compatibility with the current situation, in which only two
161	system-defined sets exist can be kept in one of two ways:
162
163	1. Leaving the situation as is - the 'world' and 'system' sets are
164	hard-coded in Portage.
165	2. Distributing default 'system' and 'world' files under the
166	``/etc/portage/sets/`` directory.
167
168	Other than that, there are no other backwards compatibility concerns
169	involved.
170
171	References
172	==========
173
174	.. [#NAME-RULES] Gentoo Linux Development Policy - Ebuild Policy
175	(http://www.gentoo.org/doc/en/policy.xml#doc_chap3)
176
177	.. [#PORTAGE-MANPAGE]
178	http://www.gentoo.org/cgi-bin/viewcvs.cgi/portage/man/portage.5?root=gentoo-src
179
180	Copyright
181	=========
182
183	This document has been placed in the public domain.
184