Bump pip from 18.1 to 21.1

[dependabot[bot]]

Bumps pip from 18.1 to 21.1.

Changelog

Sourced from pip's changelog.

21.1 (2021-04-24)

Process

• Start installation scheme migration from distutils to sysconfig. A warning is implemented to detect differences between the two implementations to encourage user reports, so we can avoid breakages before they happen.

Features

• Add the ability for the new resolver to process URL constraints. ([#8253](https://github.com/pypa/pip/issues/8253) <https://github.com/pypa/pip/issues/8253>_)
• Add a feature --use-feature=in-tree-build to build local projects in-place when installing. This is expected to become the default behavior in pip 21.3; see Installing from local packages <https://pip.pypa.io/en/stable/user_guide/#installing-from-local-packages>_ for more information. ([#9091](https://github.com/pypa/pip/issues/9091) <https://github.com/pypa/pip/issues/9091>_)
• Bring back the "(from versions: ...)" message, that was shown on resolution failures. ([#9139](https://github.com/pypa/pip/issues/9139) <https://github.com/pypa/pip/issues/9139>_)
• Add support for editable installs for project with only setup.cfg files. ([#9547](https://github.com/pypa/pip/issues/9547) <https://github.com/pypa/pip/issues/9547>_)
• Improve performance when picking the best file from indexes during pip install. ([#9748](https://github.com/pypa/pip/issues/9748) <https://github.com/pypa/pip/issues/9748>_)
• Warn instead of erroring out when doing a PEP 517 build in presence of --build-option. Warn when doing a PEP 517 build in presence of --global-option. ([#9774](https://github.com/pypa/pip/issues/9774) <https://github.com/pypa/pip/issues/9774>_)

Bug Fixes

• Fixed --target to work with --editable installs. ([#4390](https://github.com/pypa/pip/issues/4390) <https://github.com/pypa/pip/issues/4390>_)
• Add a warning, discouraging the usage of pip as root, outside a virtual environment. ([#6409](https://github.com/pypa/pip/issues/6409) <https://github.com/pypa/pip/issues/6409>_)
• Ignore .dist-info directories if the stem is not a valid Python distribution name, so they don't show up in e.g. pip freeze. ([#7269](https://github.com/pypa/pip/issues/7269) <https://github.com/pypa/pip/issues/7269>_)
• Only query the keyring for URLs that actually trigger error 401. This prevents an unnecessary keyring unlock prompt on every pip install invocation (even with default index URL which is not password protected). ([#8090](https://github.com/pypa/pip/issues/8090) <https://github.com/pypa/pip/issues/8090>_)
• Prevent packages already-installed alongside with pip to be injected into an isolated build environment during build-time dependency population. ([#8214](https://github.com/pypa/pip/issues/8214) <https://github.com/pypa/pip/issues/8214>_)
• Fix pip freeze permission denied error in order to display an understandable error message and offer solutions. ([#8418](https://github.com/pypa/pip/issues/8418) <https://github.com/pypa/pip/issues/8418>_)
• Correctly uninstall script files (from setuptools' scripts argument), when installed with --user. ([#8733](https://github.com/pypa/pip/issues/8733) <https://github.com/pypa/pip/issues/8733>_)
• New resolver: When a requirement is requested both via a direct URL (req @ URL) and via version specifier with extras (req[extra]), the resolver will now be able to use the URL to correctly resolve the requirement with extras. ([#8785](https://github.com/pypa/pip/issues/8785) <https://github.com/pypa/pip/issues/8785>_)
• New resolver: Show relevant entries from user-supplied constraint files in the error message to improve debuggability. ([#9300](https://github.com/pypa/pip/issues/9300) <https://github.com/pypa/pip/issues/9300>_)
• Avoid parsing version to make the version check more robust against lousily debundled downstream distributions. ([#9348](https://github.com/pypa/pip/issues/9348) <https://github.com/pypa/pip/issues/9348>_)
• --user is no longer suggested incorrectly when pip fails with a permission error in a virtual environment. ([#9409](https://github.com/pypa/pip/issues/9409) <https://github.com/pypa/pip/issues/9409>_)
• Fix incorrect reporting on Requires-Python conflicts. ([#9541](https://github.com/pypa/pip/issues/9541) <https://github.com/pypa/pip/issues/9541>_)

... (truncated)

Commits

• 2b2a268 Bump for release
• ea761a6 Update AUTHORS.txt
• 2edd3fd Postpone a deprecation to 21.2
• 3cccfbf Rename mislabeled news fragment
• 21cd124 Fix NEWS.rst placeholder position
• e46bdda Merge pull request #9827 from pradyunsg/fix-git-improper-tag-handling
• 0e4938d :newspaper:
• ca832b2 Don't split git references on unicode separators
• 1320bac Merge pull request #9814 from pradyunsg/revamp-ci-apr-2021-v2
• e9cc23f Skip checks on PRs only
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot close will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)
• @dependabot use these labels will set the current labels as the default for future PRs for this repo and language
• @dependabot use these reviewers will set the current reviewers as the default for future PRs for this repo and language
• @dependabot use these assignees will set the current assignees as the default for future PRs for this repo and language
• @dependabot use this milestone will set the current milestone as the default for future PRs for this repo and language

You can disable automated security fix PRs for this repo from the Security Alerts page.