This patch adds support for `--use-feature` in requirements files
so that a project that wants all contributors using the same pip
features can specify it in the requirements file. For example, to ensure
a requirements file uses the new resolver:
```
--use-feature=2020-resolver
boto3
boto3==1.13.13
```
This is a new version of #8293.
Toward minimizing style changes in the overall PR diff, or toward
consistency with the future use of black (in cases where I wasn't sure
of a good way to minimize the diff).
This is a much better location for these errors, since they're in a much
more visible spot. We've had reports in the past of users missing these
messages, and changing where we present these warnings should help
resolve that issue.
We do lose the ability for an advanced user to potentially see the
warning and abort installation before the conflicts are introduced, but
given that we don't even pause for input, I don't think that's a strong
argument and neither do I view this as necessary.
The duplication of this code isn't really that bad, but saying
"pip check" makes it ambigous which file is relevant. Changing to
reference the exact filename makes this clearer.
This requirements format does not conform to PEP-508. Currently the
extras specified like this work by accident (because _strip_extras()
also parses them). The version checks end up being done with a
misparsed version '1.0[extra]' -- this is not changed in this commit.
Add deprecation warning and fix the corresponding resolver test. Add a
command line test.
Note that we really only check that the Requirement has SpecifierSet
with a specifier that ends in a ']'. A valid version number cannot
contain ']' and no wheels currently on pypi have versions ending in ']'.
The current tests didn't catch the bug that the new tests do,
so they have been removed. Using higher-level tests can give us more
confidence that things work end-to-end and are less likely to get in
the way of refactoring.
The new test has been marked xfail since the bug is still present.
Moving this value up from `_install_wheel` means that we do not need to
pass `req_description` anymore. This will also let us move our
entrypoint error handling around without worrying about losing the
context from the previous message.