Fix --generate-hashes with bare VCS URLs

[jcushman]

#807 introduced an unhandled edge case when bare VCS URLs like git+git://github.com/jazzband/pip-tools@7d86c8d3ecd1faa6be11c7ddc6b29a30ffd1dae3 are used with pip-compile --generate-hashes:

$ cat requirements.in
git+https://github.com/jazzband/pip-tools@7d86c8d3ecd1faa6be11c7ddc6b29a30ffd1dae3
$ pip-compile --generate-hashes
Traceback (most recent call last):
  File "/Users/jcwork/.pyenv/versions/pip-tools/bin/pip-compile", line 11, in <module>
    load_entry_point('pip-tools', 'console_scripts', 'pip-compile')()
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/Users/jcwork/Documents/pip-tools/piptools/scripts/compile.py", line 357, in cli
    hashes = resolver.resolve_hashes(results)
  File "/Users/jcwork/Documents/pip-tools/piptools/resolver.py", line 88, in resolve_hashes
    return {ireq: self.repository.get_hashes(ireq) for ireq in ireqs}
  File "/Users/jcwork/Documents/pip-tools/piptools/resolver.py", line 88, in <dictcomp>
    return {ireq: self.repository.get_hashes(ireq) for ireq in ireqs}
  File "/Users/jcwork/Documents/pip-tools/piptools/repositories/local.py", line 78, in get_hashes
    return self.repository.get_hashes(ireq)
  File "/Users/jcwork/Documents/pip-tools/piptools/repositories/pypi.py", line 299, in get_hashes
    return {self._get_file_hash(cached_link)}
  File "/Users/jcwork/Documents/pip-tools/piptools/repositories/pypi.py", line 323, in _get_file_hash
    with open_local_or_remote_file(location, self.session) as f:
  File "/Users/jcwork/.pyenv/versions/3.5.3/lib/python3.5/contextlib.py", line 59, in __enter__
    return next(self.gen)
  File "/Users/jcwork/Documents/pip-tools/piptools/repositories/pypi.py", line 397, in open_local_or_remote_file
    response = session.get(url, headers=headers, stream=True)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/pip/_vendor/requests/sessions.py", line 546, in get
    return self.request('GET', url, **kwargs)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/pip/_internal/download.py", line 439, in request
    return super(PipSession, self).request(method, url, *args, **kwargs)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/pip/_vendor/requests/sessions.py", line 533, in request
    resp = self.send(prep, **send_kwargs)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/pip/_vendor/requests/sessions.py", line 640, in send
    adapter = self.get_adapter(url=request.url)
  File "/Users/jcwork/.pyenv/versions/3.5.3/envs/pip-tools/lib/python3.5/site-packages/pip/_vendor/requests/sessions.py", line 731, in get_adapter
    raise InvalidSchema("No connection adapters were found for '%s'" % url)
pip._vendor.requests.exceptions.InvalidSchema: No connection adapters were found for 'git+https://github.com/jazzband/pip-tools@7d86c8d3ecd1faa6be11c7ddc6b29a30ffd1dae3'

This is because PyPIRepository.get_hashes incorrectly detects all non-editable URLs as hashable, instead of only artifact URLs.

This PR does two things in separate commits (so you can confirm the failing behavior and test case if you want):

• Add a failing test case by having test_url_package try all URLs with and without --generate-hashes
• Fix the test case by updating get_hashes to use a better hashability check, modeled on the hashability logic in pip's RequirementPreparer.prepare_linked_requirement

Changelog-friendly one-liner: Fix --generate-hashes with bare VCS URLs

Contributor checklist

• Provided the tests for the changes.
• Requested a review from another contributor.
• Gave a clear one-line description in the PR (that the maintainers can add to CHANGELOG.md on release).
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[codecov]

Codecov Report

Merging #812 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #812      +/-   ##
==========================================
+ Coverage   98.83%   98.83%   +<.01%     
==========================================
  Files          36       36              
  Lines        2147     2150       +3     
  Branches      278      279       +1     
==========================================
+ Hits         2122     2125       +3     
  Misses         15       15              
  Partials       10       10

Impacted Files	Coverage Δ
piptools/repositories/pypi.py	93.84% <100%> (+0.06%)	⬆️
tests/test_cli_compile.py	100% <100%> (ø)	⬆️

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[atugushev]

LGTM 👍

[atugushev]

@jcushman squash please commits.

[jcushman]

Squashed!

[atugushev]

pip-tools v3.8.0 is released