PEP 631: Dependency specification in pyproject.toml based on PEP 508 (#1571)

* PEP 631: Dependency specification in pyproject.toml

pep-0631.rst

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+PEP: 631
+Title: Dependency specification in pyproject.toml based on PEP 508
+Author: Ofek Lev <ofekmeister@gmail.com>
+Sponsor: Paul Ganssle <paul@ganssle.io>
+Discussions-To: https://discuss.python.org/t/5018
+Status: Draft
+Type: Standards Track
+Content-Type: text/x-rst
+Created: 20-Aug-2020
+Post-History: 20-Aug-2020
+
+
+Abstract
+========
+
+This PEP specifies how to write a project's dependencies in a
+``pyproject.toml`` file for packaging-related tools to consume
+using the `fields defined in PEP 621`_.
+
+Entries
+=======
+
+All dependency entries MUST be valid `PEP 508 strings`_.
+
+Build backends SHOULD abort at load time for any parsing errors.
+
+::
+
+    from packaging.requirements import InvalidRequirement, Requirement
+
+    ...
+
+    try:
+        Requirement(entry)
+    except InvalidRequirement:
+        # exit
+
+Specification
+=============
+
+dependencies
+------------
+
+- Format: array of strings
+- Related core metadata:
+
+  - `Requires-Dist`_
+
+Every element must be an `entry <#entries>`_.
+
+::
+
+    [project]
+    dependencies = [
+      'PyYAML ~= 5.0',
+      'requests[security] < 3',
+      'subprocess32; python_version < "3.2"',
+    ]
+
+optional-dependencies
+---------------------
+
+- Format: table
+- Related core metadata:
+
+  - `Provides-Extra`_
+  - `Requires-Dist`_
+
+Each key is the name of the provided option, with each value being the same type as
+the `dependencies <#dependencies>`_ field i.e. an array of strings.
+
+::
+
+    [project.optional-dependencies]
+    tests = [
+      'coverage>=5.0.3',
+      'pytest',
+      'pytest-benchmark[histogram]>=3.2.1',
+    ]
+
+Example
+=======
+
+This is a real-world example port of what `docker-compose`_ defines.
+
+::
+
+    [project]
+    dependencies = [
+      'cached-property >= 1.2.0, < 2',
+      'distro >= 1.5.0, < 2',
+      'docker[ssh] >= 4.2.2, < 5',
+      'dockerpty >= 0.4.1, < 1',
+      'docopt >= 0.6.1, < 1',
+      'jsonschema >= 2.5.1, < 4',
+      'PyYAML >= 3.10, < 6',
+      'python-dotenv >= 0.13.0, < 1',
+      'requests >= 2.20.0, < 3',
+      'texttable >= 0.9.0, < 2',
+      'websocket-client >= 0.32.0, < 1',
+
+      # Conditional
+      'backports.shutil_get_terminal_size == 1.0.0; python_version < "3.3"',
+      'backports.ssl_match_hostname >= 3.5, < 4; python_version < "3.5"',
+      'colorama >= 0.4, < 1; sys_platform == "win32"',
+      'enum34 >= 1.0.4, < 2; python_version < "3.4"',
+      'ipaddress >= 1.0.16, < 2; python_version < "3.3"',
+      'subprocess32 >= 3.5.4, < 4; python_version < "3.2"',
+    ]
+
+    [project.optional-dependencies]
+    socks = [ 'PySocks >= 1.5.6, != 1.5.7, < 2' ]
+    tests = [
+      'ddt >= 1.2.2, < 2',
+      'pytest < 6',
+      'mock >= 1.0.1, < 4; python_version < "3.4"',
+    ]
+
+Copyright
+=========
+
+This document is placed in the public domain or under the
+CC0-1.0-Universal license, whichever is more permissive.
+
+
+.. _fields defined in PEP 621: https://www.python.org/dev/peps/pep-0621/#dependencies-optional-dependencies
+.. _PEP 508 strings: https://www.python.org/dev/peps/pep-0508/
+.. _Requires-Dist: https://packaging.python.org/specifications/core-metadata/#requires-dist-multiple-use
+.. _Provides-Extra: https://packaging.python.org/specifications/core-metadata/#provides-extra-multiple-use
+.. _docker-compose: https://github.com/docker/compose/blob/789bfb0e8b2e61f15f423d371508b698c64b057f/setup.py#L28-L61
+
+..
+   Local Variables:
+   mode: indented-text
+   indent-tabs-mode: nil
+   sentence-end-double-space: t
+   fill-column: 70
+   coding: utf-8
+   End: