iSharkFly-Open
/
python-peps
mirror of https://github.com/python/peps.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Recording the Direct URL Origin of installed distributions (#1145)

This commit is contained in:
Stéphane Bidoul (ACSONE) 2019-11-14 18:41:21 +01:00 committed by Brett Cannon
parent da480869f8
commit 1e094877fd
1 changed files with 508 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

508
pep-9999.rst Normal file
View File

@ -0,0 +1,508 @@
PEP: 9999
Title: Recording the Direct URL Origin of installed distributions
Author: Stéphane Bidoul <stephane.bidoul@acsone.eu>, Chris Jerdonek <chris.jerdonek@gmail.com>
Discussions-To: https://discuss.python.org/t/recording-the-source-url-of-an-installed-distribution/1535
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 21-Apr-2019
Post-History:
Abstract
========
Following PEP 440, a distribution can be identified by a name and either a
version, or a direct URL reference (see `PEP440 Direct References`_).
After installation, the name and version are captured in the project metadata,
but currently there is no way to obtain details of the URL used when the
distribution was identified by a direct URL reference.
This proposal defines
additional metadata, to be added to the installed distribution by the
installation front end, which records the Direct URL Origin for use by
consumers which introspect the database of installed packages (see PEP 376).
Motivation
==========
The original motivation of this PEP was to permit tools with a "freeze"
operation allowing a Python environment to be recreated to work in a broader
range of situations.
Specifically, the PEP originated from the desire to address `pip issue #609`_:
i.e. improving the behavior of ``pip freeze`` in the presence of distributions
installed from direct URL references. It follows a
`thread on discuss.python.org`_ about the best course of action to implement
it.
Installation from direct URL references
---------------------------------------
Python installers such as pip are capable of downloading and installing
distributions from package indexes. They are also capable of downloading
and installing source code from requirements specifying arbitrary URLs of
source archives and Version Control Systems (VCS) repositories,
as standardized in `PEP440 Direct References`_.
In other words two relevant installation modes exist.
1. the package to install is specified as a name and version specifier:
In this case, the installer looks in a package index (or optionally
using ``--find-links`` in the case of pip) to find the distribution to install.
2. The package to install is specified as a direct URL reference:
In this case, the installer downloads whatever is specified by the URL
(typically a wheel, a source archive or a VCS repository) and installs it.
In this mode, installers typically download the source code in a
temporary directory, invoke the PEP 517 build backend to produce a wheel
if needed, install the wheel, and delete the temporary directory.
After installation, no trace of the URL the user requested to download the
package is left on the user system.
Freezing an environment
-----------------------
Pip also sports a command named ``pip freeze`` which examines the Database of
Installed Python Distributions to generate a list of requirements. The main
goal of this command is to help users generating a list of requirements that
will later allow the re-installation the same environment with the highest
possible fidelity.
The ``pip freeze`` command outputs a ``name==version`` line for each installed
distribution (except for editable installs). To achieve the goal of
reinstalling the same environment, this requires the (name, version)
tuple to refer to an immutable version of the
distribution. The immutability is guaranteed by package indexes
such as Warehouse. The package index to use is typically known from
environmental or command line parameters of the installer.
This freeze mechanism therefore works fine for installation mode 1 (i.e.
when the package to install was specified as a name plus version specifier).
For installation mode 2, i.e. when the package to install was specified as a
direct URL reference, the ``name==version`` tuple is obviously not sufficient
to reinstall the same distribution and users of the freeze command expect it
to output the URL that was originally requested.
The reasoning above is equally applicable to tools, other than ``pip freeze``,
that would attempt to generate a ``Pipfile.lock`` or any other similar format
from the Database of Installed Python Distributions. Unless specified
otherwise, "freeze" is used in this document as a generic term for such
an operation.
The importance of installing from (VCS) URLs for application integrators
------------------------------------------------------------------------
For an application integrator, it is important to be able to reliably install
and freeze unreleased version of python distributions.
For instance when a developer needs to deploy an unreleased patched version
of a dependency, it is common to install the dependency directly from a VCS
branch that has the patch, while waiting for the maintainer to release an
updated version.
In such cases, it is important for "freeze" to pin the exact VCS
reference (commit-hash if available) that was installed, in order to create
reproducible builds with the highest possible fidelity.
Additional origin metadata available for VCS URLs
-------------------------------------------------
For VCS URLs, there is additional origin information available only at
install time useful for introspection and certain workflows. For example,
when installing a revision from a VCS URL, a tool can determine if the
revision corresponds to a branch, tag or (in the case of Git) a ref. This
information can be used when introspecting the database of installed packages
to communicate to users more information about what version was installed
(e.g. whether a branch or tag was installed and, if so, the name of the
branch or tag). This also permits one to know whether a PEP 440 direct
reference URL can be constructed using the tag form, as only tags have the
semantics of immutability.
In cases where the revision is mutable (e.g. branches and Git refs), knowing
this information enables workflows where users can e.g. update to the latest
version of a branch they are tracking, or update to the latest version of a
pull request they are reviewing locally. In contrast, when the revision is a
tag, tools can know in advance (e.g. without network calls) that no update is
needed.
As with the URL itself, if this information isn't recorded at install time
when the VCS repository is available, it would otherwise be lost.
Note about "editable" installs
------------------------------
The editable installation mode of pip roughly lets a user insert a
local directory in sys.path for development purpose. This mode is somewhat
abused to work around the fact that a non-editable install from a VCS URL
loses track of the origin after installation.
Indeed editable installs implicitly record the VCS origin in the checkout
directory, so the information can be recovered when running "freeze".
The use of this workaround, although useful, is fragile, creates confusion
about the purpose of the editable mode, and works only when the distribution
can be installed with setuptools (i.e. it is not usable with other PEP 517
build backends).
For the sake of clarity, it is important to note that this PEP is otherwise
unrelated to editable installs.
Rationale
=========
This PEP specifies a new ``direct_url.json`` metadata file in the
``.dist-info`` directory of an installed distribution.
The fields specified are sufficient to reproduce the source archive and `VCS
URLs supported by pip`_. They are also sufficient to reproduce `PEP440 Direct
References`_, as well as `Pipfile and Pipfile.lock`_ entries. Finally, they
are sufficient to record the branch, tag, and/or Git ref origin of the
installed version that is already available for editable installs by virtue
of a VCS checkout being present.
Since at least three different ways already exist to encode this type of
information, this PEP uses a key-value format, so as not to make any
assumption on how a direct
URL reference must ultimately be encoded in a requirement or lockfile. See also
the `Alternatives`_ section below for more discussion about this choice.
Information has been taken from Ruby's bundler manual to verify it has similar
capabilities and inform the selection and naming of fields in this
specifications.
The JSON format allows for the addition of additional fields in the future.
Specification
=============
This PEP specifies a ``direct_url.json`` file in the ``.dist-info`` directory
of an installed distribution, to record the Direct URL Origin of the distribution.
This file MUST be created by installers when installing a distribution
from a requirement specifying a direct URL reference (including a VCS URL)
in *non*-editable mode.
This file MUST NOT be created when installing a distribution from an other
type of requirement (i.e. name plus version specifier, or URL in editable mode).
This JSON MUST be a flat dictionary where all keys and values are of string type.
For the sake of forward compatibility, tools SHOULD ignore values which are
not of string type.
If present, it MUST contain at least one field with name ``url``.
``url`` MUST be stripped of any sensitive authentication information,
for security reasons. The user:password section of the URL MAY however
be composed of environment variables, matching the following regular
expression::
\$\{[A-Za-z0-9-_]+\}(:\$\{[A-Za-z0-9-_]+\})?
When ``url`` refers to a VCS repository:
- A ``vcs`` field MUST be present, containing the name of the VCS
(i.e. one of ``git``, ``hg``, ``bzr``, ``svn``). Other VCS's SHOULD be registered by
amending this PEP.
- The ``url`` value MUST be compatible with the corresponding VCS,
so an installer can hand it off without transformation to a
checkout/download command of the VCS.
- A ``requested_revision`` field MAY be present naming a
branch/tag/ref/commit/revision/etc (in a format compatible with the VCS)
to install.
- A ``commit_id`` field MUST be present, containing the
exact commit/revision number that was installed.
If the VCS supports commit-hash
based revision identifiers, such commit-hash MUST be used as
``commit_id`` in order to reference the immutable
version of the source code that was installed.
- A ``tag`` field naming a tag MAY be present to indicate that a particular
tag was installed.
- A ``branch`` field naming a branch MAY be present to indicate that a
particular branch was installed. If ``branch`` is present, ``tag`` MUST not
be present.
When ``url`` refers to a source archive, a wheel, or a local directory:
- A ``hash`` field SHOULD be present, with value
``<hash-algorithm>=<expected-hash>``.
It is RECOMMENDED that only hashes which are unconditionally provided by
the latest version of the standard library's ``hashlib`` module be used for
source archive hashes. At time of writing, that list consists of 'md5',
'sha1', 'sha224', 'sha256', 'sha384', and 'sha512'.
.. note::
When the requested URL points to a local directory that happens to contain a
VCS checkout, installers MUST NOT attempt to infer any VCS information and
therefore MUST NOT output any vcs related information (such as the ``vcs`` field)
in ``direct_url.json``.
A ``subdirectory`` field MAY be present containing a directory path,
relative to the root of the VCS repository, source archive or local directory,
to specify where ``pyproject.toml`` or ``setup.py`` is located.
.. note::
As a general rule, installers should as much as possible preserve the
information that was provided in the requested URL when generating
``direct_url.json``. For example user:password environment variables
should be preserved and ``requested_revision`` should reflect the revision that was
provided in the requested URL as faithfully as possible. This information is
however *enriched* with more precise data, such as ``commit_id``.
Registered VCS
--------------
This section lists the registered VCS's; expanded, VCS-specific information
on how to use the ``vcs``, ``requested_revision``, and other fields; and in
some cases additional VCS-specific fields.
Tools MAY support other VCS's although it is RECOMMENDED to register
them by amending this PEP. The ``vcs`` field SHOULD be the command name
(lowercased). Additional fields that would be necessary to
support such VCS SHOULD be prefixed with the VCS command name.
Git
+++
Home page
https://git-scm.com/
vcs command
git
vcs field
git
requested_revision field
A tag name, branch name, Git ref, commit hash, shortened commit hash,
or other commit-ish.
commit_id field
A commit hash (40 hexadecimal characters sha1).
branch field
If no ``requested_revision`` is provided and the remote repository has
a default branch, this field can be used to record the default branch that
was installed.
VCS-specific fields:
- A ``git_ref`` field naming a Git ref (string beginning with ``refs/``) MAY
be present to indicate that a particular ref was installed (e.g.
``refs/pull/123/head``).
.. note::
Installers can use the ``git show-ref`` and ``git symbolic-ref`` commands
to determine if the ``requested_revision`` corresponds to a Git ref.
In turn, a ref beginning with ``refs/tags/`` corresponds to a tag, and
a ref beginning with ``refs/remotes/origin/`` after cloning corresponds
to a branch.
Mercurial
+++++++++
Home page
https://www.mercurial-scm.org/
vcs command
hg
vcs field
hg
requested_revision field
A tag name, branch name, changeset ID, shortened changeset ID.
commit_id field
A changeset ID (40 hexadecimal characters).
Bazaar
++++++
Home page
https://bazaar.canonical.com/
vcs command
bzr
vcs field
bzr
requested_revision field
A tag name, branch name, revision id.
commit_id field
A revision id.
Subversion
++++++++++
Home page
https://subversion.apache.org/
vcs command
svn
vcs field
svn
requested_revision field
``requested_revision`` must be compatible with ``svn checkout`` ``--revision`` option.
In Subversion, branch or tag is part of ``url``.
commit_id
Since Subversion does not support globally unique identifiers,
this field is the Subversion revision number in the corresponding
repository.
Examples
========
Example direct_url.json
-----------------------
Source archive:
.. code::
{
"url": "https://github.com/pypa/pip/archive/1.3.1.zip",
"hash": "sha256=2dc6b5a470a1bde68946f263f1af1515a2574a150a30d6ce02c6ff742fcc0db8"
}
Git URL with tag and commit-hash:
.. code::
{
"url": "https://github.com/pypa/pip.git",
"vcs": "git",
"requested_revision": "1.3.1",
"commit_id": "7921be1537eac1e97bc40179a57f0349c2aee67d"
}
Example pip commands and their effect on direct_url.json
--------------------------------------------------------
Commands that generate a ``direct_url.json``:
* pip install https://example.com/app-1.0.tgz
* pip install https://example.com/app-1.0.whl
* pip install "git+https://example.com/repo/app.git#egg=app&subdirectory=setup"
* pip install ./app
* pip install file:///home/user/app
Commands that *do not* generate a ``direct_url.json``
* pip install app
* pip install app --no-index --find-links https://example.com/
* pip install --editable "git+https://example.com/repo/app.git#egg=app&subdirectory=setup"
* pip install -e ./app
Use cases
=========
"Freezing" an environment
Tools, such as ``pip freeze``, which generate requirements from the Database
of Installed Python Distributions SHOULD exploit ``direct_url.json``
if it is present, and give it priority over the Version metadata in order
to generate a higher fidelity output. In the presence of a ``vcs`` direct URL reference,
the ``commit_id`` field SHOULD be used in priority in order to provide
the highest possible fidelity to the originally installed version. If
supported by their requirement format, tools are encouraged also to output
the ``tag`` value if present, as it has immutable semantics.
Tools MAY choose another approach, depending on the needs of their users.
Backwards Compatibility
=======================
Since this PEP specifies a new file in the ``.dist-info`` directory,
there are no backwards compatibility implications.
Alternatives
============
PEP426 source_url
-----------------
The now withdrawn PEP 426 specifies a ``source_url`` metadata entry.
It is also implemented in `distlib`_.
It was intended for a slightly different purpose, for use in sdists.
This format lacks support for the ``subdirectory`` option of pip requirement
URLs. The same limitation is present in `PEP440 Direct References`_.
It also lacks explicit support for `environment variables in the user:password
part of URLs`_.
The introduction of a key/value extensibility mechanism and support
for environment variables for user:password in PEP 440, would be necessary
for use in this PEP.
revision vs ref
---------------
The ``requested_revision`` key was retained over ``requested_ref`` as it is a more generic term
across various VCS and ``ref`` has a specific meaning for ``git``.
References
==========
.. _`pip issue #609`: https://github.com/pypa/pip/issues/609
.. _`thread on discuss.python.org`: https://discuss.python.org/t/pip-freeze-vcs-urls-and-pep-517-feat-editable-installs/1473
.. _PEP440: http://www.python.org/dev/peps/pep-0440
.. _`VCS URLs supported by pip`: https://pip.pypa.io/en/stable/reference/pip_install/#vcs-support
.. _`PEP440 Direct References`: https://www.python.org/dev/peps/pep-0440/#direct-references
.. _`Pipfile and Pipfile.lock`: https://github.com/pypa/pipfile
.. _distlib: https://distlib.readthedocs.io
.. _`environment variables in the user:password part of URLs`: https://pip.pypa.io/en/stable/reference/pip_install/#id10
Acknowledgements
================
Various people helped make this PEP a reality. Paul F. Moore provided the
essence of the abstract. Nick Coghlan suggested the direct_url name.
Copyright
=========
This document is placed in the public domain or under the
CC0-1.0-Universal license, whichever is more permissive.
..
Local Variables:
mode: indented-text
indent-tabs-mode: nil
sentence-end-double-space: t
fill-column: 70
coding: utf-8
End: