en/glep/glep-0021.txt

GLEP: 21
Title: User-defined Package Sets
Version: $Revision: 1.2 $ 
Last-Modified: $Date: 2004/03/07 23:20:54 $
Author: Tal Peer <coredumb@gentoo.org>,
        Alec Warner <antarus@gentoo.org>
Status: Draft
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
======

Taken over by antarus.


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	g2boojum	1.1	GLEP: 21
2			Title: User-defined Package Sets
3	g2boojum	1.3	Version: $Revision: 1.2 $
4			Last-Modified: $Date: 2004/03/07 23:20:54 $
5			Author: Tal Peer <coredumb@gentoo.org>,
6			Alec Warner <antarus@gentoo.org>
7	g2boojum	1.1	Status: Draft
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	g2boojum	1.3	Post-History: 6-Mar-2004, 3-Sep-2006
13
14			Status
15			======
16
17			Taken over by antarus.
18	g2boojum	1.1
19
20			Abstract
21			========
22
23			In Portage, package sets (formerly known as 'classes' or 'targets')
24			are mere groups of packages, grouped together to allow easier updating
25			and handling of them. Currently it is impossible to define sets further
26			than the two default ones: "system" and "world".
27
28			Motivation
29			==========
30
31			Over the months, quite a few requests for user-defined sets were
32			made by users and developers, either by posting bugs, messages to
33			mailing lists or on IRC. Usually the response is that this is an
34			awesome idea, but no one ever took the time to actually define it
35			properly and implement it.
36
37			This document offers a specification for the implementation of
38			user-defined sets using configuration files similar to the current
39			world/system sets use.
40
41			Specification
42			=============
43
44			The proposed implementation uses a one file per set approach, meaning
45			each package set is defined in a single file. All set definition files
46			will reside in a directory ``/etc/portage/sets/`` and each set's name
47			will be its file name. Therefore, if one defines a set in
48			/etc/portage/sets/foo-set, the set name will be 'foo-set'. Usual
49			package naming rules [#NAME-RULES]_ also apply to sets.
50
51			As it is impossible to create two or more files with identical names
52			in the same directory, a theoretic conflict between two different sets
53			sharing the same name is impossible. However, users may define a
54			package set whose name conflicts with one more or packages (for ambiguity
55			resolution, see below).
56
57			Syntax for the package list file is the same as the world file syntax,
58			as described in the Portage manpage [#PORTAGE-MANPAGE]_, with one
59			addition: sets may not be 'inherited' by other sets, only packages may
60			be listed. There is no limitation to the number of packages in a set
61			or to the number of sets a package may belong to.
62
63			Using User-defined Sets With Emerge
64			--------------------------------------
65
66			The user-defined sets will be available either directly or using
67			the --package-set option, As in::
68
69			# Basically the same:
70			emerge foo-set
71			emerge --package-set foo-set
72
73			The --package-set option is introduced to bypass ambiguities, as
74			illustrated in the next example::
75
76			emerge foo # Where foo is both a set and a one or more
77			# existing packages. This will cause emerge to show
78			# the ambiguity, ask us to be more
79			# specific, and stop.
80
81			emerge --package-set foo # So we specify that what we actually
82			# meant was the package set.
83
84			emerge cat-bar/foo # Or we specify the exact package name.
85
86			When running emerge with the --pretend option, sets will be
87			expanded to the packages they are comprised off in the output, as with
88			the current system-defined sets.
89
90			Only one set may be passed to portage at time, and sets can not
91			be mixed with ordinary packages. Thus, the following snippets are
92			all invalid and will result in an error (assuming ``foo-set`` and
93			``bar-set`` are defined as sets)::
94
95			emerge foo-set glibc
96			emerge bar-set system
97			emerge world foo-set gcc
98
99			Compatibility With Other Portage Features
100			-----------------------------------------
101
102			* Dependencies:
103			Package sets (both system-defined and user-defined) may not be
104			depended on by ordinary packages and eclasses.
105
106			* package.mask:
107			Masking a package set through the ``package.mask`` file is forbidden.
108	g2boojum	1.2	In order to 'mask' a package set, one should move it away from the
109			sets directory.
110	g2boojum	1.1
111			* package.use:
112			USE flags may not be defined for sets in the ``package.use`` file.
113
114			Implementation
115			==============
116
117			The implementation of the package sets concept in Portage should be
118			mostly done in portage.py, and only the interface parts should be
119			added to emerge itself, to keep the separation between interface and
120			logic.
121
122			The amount of work needed for implementation is not trivial, but not
123			huge either.
124
125			Rationale
126			=========
127
128			The one file per set approach makes it easy to list the sets which are
129			defined on a system by just listing the ``/etc/portage/sets``
130			directory contents. Additionally, it makes the set lookup process more
131			efficient as it only requires to check if a file exists.
132
133			I chose the --package-set option over the --set option for explicitly
134			telling portage to emerge a set mostly because --set implies setting
135			an environment variable, or such.
136
137			Allowing sets' USE flags to be manipulated through the ``package.use``
138			file would have done more harm than good, for several reasons:
139
140			- If a USE flag is turned on (i.e. 'foo') for a set and the same USE
141			flag is turned off (i.e. '-foo'), for a package which is part of
142			the set, it is unclear which setting should take precedence.
143
144			- Similarly, if a USE flag is turned on for a set and the same USE flag
145			is turned off for a set that is a subset of the original set, it is
146			unclear which setting should take precedence.
147
148			- If a USE flag is defined (either off or on) for a set and a package
149			that belongs in the set is to be emerged, it is unclear whether the
150			USE flag should be defined when emerging the package in question.
151
152			Therefore, I have decided it would be better to disallow setting USE
153			flags for sets.
154
155			Backwards Compatibility
156			=======================
157
158			Backwards compatibility with the current situation, in which only two
159			system-defined sets exist can be kept in one of two ways:
160
161			1. Leaving the situation as is - the 'world' and 'system' sets are
162			hard-coded in Portage.
163			2. Distributing default 'system' and 'world' files under the
164			``/etc/portage/sets/`` directory.
165
166			Other than that, there are no other backwards compatibility concerns
167			involved.
168
169			References
170			==========
171
172			.. [#NAME-RULES] Gentoo Linux Development Policy - Ebuild Policy
173			(http://www.gentoo.org/doc/en/policy.xml#doc_chap3)
174
175			.. [#PORTAGE-MANPAGE]
176			http://www.gentoo.org/cgi-bin/viewcvs.cgi/portage/man/portage.5?root=gentoo-src
177
178			Copyright
179			=========
180
181			This document has been placed in the public domain.
182