py-pip: updated to 20.2

20.2
====

Deprecations and Removals
-------------------------
- Deprecate setup.py-based builds that do not generate an ``.egg-info`` directory.
- Disallow passing install-location-related arguments in ``--install-options``.
- Add deprecation warning for invalid requirements format "base>=1.0[extra]"
- Deprecate legacy setup.py install when building a wheel failed for source
  distributions without pyproject.toml
- Deprecate -b/--build/--build-dir/--build-directory. Its current behaviour is confusing
  and breaks in case different versions of the same distribution need to be built during
  the resolution process. Using the TMPDIR/TEMP/TMP environment variable, possibly
  combined with --no-clean covers known use cases.
- Remove undocumented and deprecated option ``--always-unzip``

Features
--------
- Log debugging information about pip, in ``pip install --verbose``.
- Refine error messages to avoid showing Python tracebacks when an HTTP error occurs.
- Install wheel files directly instead of extracting them to a temp directory.
- Add a beta version of pip's next-generation dependency resolver.

  Move pip's new resolver into beta, remove the
  ``--unstable-feature=resolver`` flag, and enable the
  ``--use-feature=2020-resolver`` flag. The new resolver is
  significantly stricter and more consistent when it receives
  incompatible instructions, and reduces support for certain kinds of
  :ref:`Constraints Files`, so some workarounds and workflows may
  break. More details about how to test and migrate, and how to report
  issues, at :ref:`Resolver changes 2020` . Maintainers are preparing to
  release pip 20.3, with the new resolver on by default, in October.
- Add a subcommand ``debug`` to ``pip config`` to list available configuration sources and the key-value pairs defined in them.
- Warn if index pages have unexpected content-type
- Allow specifying ``--prefer-binary`` option in a requirements file
- Generate PEP 376 REQUESTED metadata for user supplied requirements installed
  by pip.
- Warn if package url is a vcs or an archive url with invalid scheme
- Parallelize network operations in ``pip list``.
- Allow the new resolver to obtain dependency information through wheels
  lazily downloaded using HTTP range requests.  To enable this feature,
  invoke ``pip`` with ``--use-feature=fast-deps``.
- Support ``--use-feature`` in requirements files

Bug Fixes
---------
- Use canonical package names while looking up already installed packages.
- Fix normalizing path on Windows when installing package on another logical disk.
- The VCS commands run by pip as subprocesses don't merge stdout and stderr anymore, improving the output parsing by subsequent commands.
- Correctly treat non-ASCII entry point declarations in wheels so they can be
  installed on Windows.
- Update author email in config and tests to reflect decommissioning of pypa-dev list.
- Headers provided by wheels in .data directories are now correctly installed
  into the user-provided locations, such as ``--prefix``, instead of the virtual
  environment pip is running in.

Vendored Libraries
------------------
- Vendored htmlib5 no longer imports deprecated xml.etree.cElementTree on Python 3.
- Upgrade appdirs to 1.4.4
- Upgrade certifi to 2020.6.20
- Upgrade distlib to 0.3.1
- Upgrade html5lib to 1.1
- Upgrade idna to 2.10
- Upgrade packaging to 20.4
- Upgrade requests to 2.24.0
- Upgrade six to 1.15.0
- Upgrade toml to 0.10.1
- Upgrade urllib3 to 1.25.9

Improved Documentation
----------------------
- Add ``--no-input`` option to pip docs
- List of options supported in requirements file are extracted from source of truth,
  instead of being maintained manually.
- Fix pip config docstring so that the subcommands render correctly in the docs
- replace links to the old pypa-dev mailing list with https://mail.python.org/mailman3/lists/distutils-sig.python.org/
- Fix example for defining multiple values for options which support them
- Add documentation that helps the user fix dependency conflicts
- Add feature flags to docs
- Document how to install package extras from git branch and source distributions.

(adam)