Re: [gentoo-dev] [pre-GLEP v2] Repository configuration file (layout.conf)

[Michał Górny]

Hi,

Here's the second version.  I've attempted to make the format section
more readable, clarified the value types and added more examples all
over the place.


---
GLEP: 9999
Title: Repository configuration file (layout.conf)
Author: Michał Górny <mgorny@g.o>
Type: Standards Track
Status: Draft
Version: 1.0
Created: 2021-05-19
Last-Modified: 2021-05-19
Post-History: 2021-05-19
Content-Type: text/x-rst
---

Abstract
========

The ``metadata/layout.conf`` file format is specified as used by Portage
and pkgcore.  A standard set of configuration keys is described
including the keys currently used in the Gentoo repository.


Motivation
==========

The ``metadata/layout.conf`` file was first added to the Gentoo
repository in Oct 2011, to facilitate setting of hashes used
in Manifest2 files.  In Mar 2012, it was used to indicate the transition
to the new ``md5-dict`` cache format.  In Jul 2013, it started being
used to indicate the repository's masters and effectively became
obligatory for all repositories.

Today, ``layout.conf`` is used for various repository configuration
knobs that can be expressed as simple values and therefore
do not justify adding new files to the repository.  This primarily
involves the configuration of development tools but also includes a few
keys relevant to the behavior of the package manager.

However, ``layout.conf`` is currently not covered by any formal
specification.  The PMS neglects its existence entirely, and the keys
used are roughly defined by their first use of Portage or pkgcore.
This GLEP aims to overcome this by providing a formal specification
for the file, as well as an up-to-date list of permitted configuration
keys.


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

layout.conf file format
-----------------------

Every ebuild repository must contain a ``metadata/layout.conf`` file.
The file uses a line-oriented key-value format::

    # comments are allowed
    key = value
    key2 = value2

Lines starting with a hash sign (``#``) represent comments and are
ignored, as are lines consisting entirely of whitespace.

Key can be any string and must not contain spaces.  The exact form
of value depends on the key.  For some keys, the value is permitted
to contain spaces, and it must not be quoted.  In some cases an empty
value is permitted.  The whitespace between the elements is optional
and is ultimately stripped.  Every key must occur no more than once
in the file.


Configuration keys
------------------

This GLEP specifies a number of standard configuration keys.  New keys
may be added to it in the future.  It is strongly recommended that any
new keys are added to the specification before being used.

The package manager can implement a subset of the listed keys.  Unknown
keys should be ignored.


The following keys must be present in a ``layout.conf`` file:

masters = <space-separated repository names>
  Specifies the master repositories of this repository.  For stand-alone
  repositories, this must be set to an empty value.  Otherwise, it can
  list one or more repositories, separated by spaces.  This key must
  be specified.

  Examples::

      # most common case
      masters = gentoo
      # stand-alone repository
      masters =
      # multiple masters
      masters = gentoo python


The following keys are optional:

manifest-hashes = <space-separated hash names>
  Specifies the list of hashes that should be used for new distfiles
  in the Manifest files.  The development tools may create a subset
  of the specified hashes if it is not updating the checksums for
  the specified distfile, or does not support the hash in question.
  The hash names are specified in GLEP 74.  [#GLEP74]_  The default
  set of hashes is implementation-defined.

  Example::

      manifest-hashes = BLAKE2B SHA512

manifest-required-hashes = <space-separated hash names>
  Specifies the list of hashes that must be used in Manifest files.
  The development tools must support all the hashes listed there,
  and update distfile checksums to use these hashes (refetching
  if necessary).  This must be a subset of manifest-hashes.  If not
  specified, all hashes from manifest-hashes (or the default set)
  are considered required.

use-manifests = ``strict``, ``true`` or ``false``
  Indicates the policy for creating and using Manifest files.  If set
  to ``strict``, Manifest files are created and files are required to
  match digests found in Manifests.  If set to ``true``, Manifests
  are created but digest mismatches are ignored.  If set to ``false``,
  Manifests are not used at all.  The default is ``strict``.

update-changelog = ``true`` or ``false``
  Indicates whether the development tools should write ChangeLog files.
  The default is ``false``.

cache-formats = <space-separated format names>
  Specifies one or more cache formats used by the repository.
  The currently defined values are ``pms`` for the original format
  specified in the PMS and ``md5-dict`` for the md5-dict format
  introduced in Portage 2.2.0_alpha68.  The default is
  implementation-defined.

  Examples::

      # modern repo
      cache-formats = md5-dict
      # backwards compatibility case
      cache-formats = md5-dict pms

eapis-deprecated = <space-separated EAPI names>
  Specifies one or more EAPIs that are to be considered deprecated
  by the development tools for use in ebuilds, i.e. their use should
  trigger a warning.  If not specified, no EAPIs are deprecated.

  Example::

      eapis-deprecated = 0 1 2 3 4

eapis-banned = <space-separated EAPI names>
  Specifies one or more EAPIs that are to be considered banned
  by the development tools for use in ebuilds, i.e. their use should
  be blocked.  If not specified, no EAPIs are banned.

repo-name = <string>
  Specifies the repository name.  If specified, it must be equal
  to the contents of ``profiles/repo_name``.  If not specified,
  it defaults to the same value.  Discouraged.

aliases = <space-separated names>
  Specified one or more additional names that can be used to reference
  the repository (e.g. in repository dependencies).  If not specified,
  no aliases are defined.

  Example::

      # gen2 is a fork of Gentoo that can be used in place of the Gentoo
      # repository
      repo-name = gen2
      aliases = gentoo

thin-manifests = ``true`` or ``false``
  If enabled, Manifest files in the package directory must contain only
  ``DIST`` entries.  If disabled, Manifest files in the package
  directory must list digests for all files found in the package
  directory and the files directory.  The default is ``false``.

sign-commits = ``true`` or ``false``
  Indicates whether git commits are to be signed (using ``git commit
  --gpg-sign``.  The default is ``false``.

sign-manifests = ``true`` or ``false``
  Indicates whether individual package Manifests should be PGP-signed.
  Note that this refers to the historical behavior of signing individual
  Manifests, not the GLEP 74 behavior of signing the top-level Manifest.
  [#GLEP74]_  The default is ``true`` if PGP signing is configured.

properties-allowed = <space-separated property tokens>
  Specifies the list of ``PROPERTIES`` tokens that are permitted
  to be used in ebuilds.  If present, the development tools should issue
  a warning if ``PROPERTIES`` contains any tokens that are not listed
  here.  If not specified, all tokens are permitted.

  Example::

      properties-allowed = live

restrict-allowed = <space-separated restrict tokens>
  Same as properties-allowed, except for ``RESTRICT``.

profile-formats = <space-separated format names>
  Specifies the format used by profiles and/or extensions to it.
  The default is ``pms`` indicating the format specified in the PMS.
  Other values are implementation-defined.

  Examples::

      profile-formats = portage-1
      profile-formats = portage-2 profile-set


Complete example
----------------

The following is an example configuration for a git repository with
Gentoo set as a master::

    masters = gentoo

    # git: do not use ChangeLog, use thin, unsigned Manifests
    update-changelog = false
    thin-manifests = true
    sign-manifests = false

    # force the new md5-dict cache format
    cache-formats = md5-dict


Rationale
=========

This GLEP is written almost 10 years after ``layout.conf`` was
originally introduced.  This made it necessary to write it in such a way
that both the modern and historical implementations in Portage
and pkgcore, as well as the use in the Gentoo repository
and a reasonably large subset of the other repositories would remain
compliant.

The historical default of assuming ``masters = gentoo`` when unspecified
is omitted as it is not portable and verbosely deprecated for many
years in Portage.  All repositories are required to explicitly specify
their masters, or an empty value if they are stand-alone.

The default for Manifest hashes and cache formats are left to be
implementation-defined, as the defaults changed over time and do not
match between package managers.  In particular, Portage attempts to
autodetect the cache format currently used in a given repository.

The repo-name key has been originally added as an alternative to
``profiles/repo_name``.  However, the latter file is still required
for PMS compliance.  Furthermore, given that it is much easier to parse,
there seems to be no appealing reason to work towards replacing that
file.  This means that for all practical reasons, the repo-name key
is redundant and is listed here for completeness only.

The profile-formats key has been introduced to permit Portage-specific
extensions to the profile directory without having to introduce custom
EAPIs.  The exact extensions are considered outside the scope of this
specification.


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

The existing implementations found in Portage and pkgcore conform
to this specification, so does the ``metadata/layout.conf`` file
found in the Gentoo repository.


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

The support for ``metadata/layout.conf`` is already a part of Portage
and pkgcore.


References
==========

.. [#GLEP74] GLEP 74: Full-tree verification using Manifest files
   (https://www.gentoo.org/glep/glep-0074.html)


Copyright
=========

This work is licensed under the Creative Commons Attribution-ShareAlike 4.0
International License. To view a copy of this license, visit
https://creativecommons.org/licenses/by-sa/4.0/.



-- 
Best regards,
Michał Górny