pip hangs, lockfile can't acquire a lock, forward-slash in hostname

[cjdelisle]

Environment

• pip version: 19.1.1
• Python version: 3.7
• OS: OSX 10.10.5

My machine's hostname is ¯\_(ツ)_/¯

Description

Pip hangs on doing any action, removing the cache makes some commands (e.g. list) work once, but after the first time, it hangs again.

80e11c05d836c05103f (from https://pypi.org/simple/pip/) (requires-python:>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*), version: 19.2.3
  Found link https://files.pythonhosted.org/packages/00/9e/4c83a0950d8bdec0b4ca72afd2f9cea92d08eb7c1a768363f2ea458d08b4/pip-19.2.3.tar.gz#sha256=e7a31f147974362e6c82d84b91c7f2bdf57e4d3163d3d454e6c3e71944d
67135 (from https://pypi.org/simple/pip/) (requires-python:>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*), version: 19.2.3
There was an error checking the latest version of pip
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/pip/_vendor/lockfile/linklockfile.py", line 19, in acquire
    open(self.unique_name, "wb").close()
FileNotFoundError: [Errno 2] No such file or directory: '/Users/user/Library/Caches/pip/¯\\_(ツ)_/¯-714d9300.40509451801170741664861'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/utils/outdated.py", line 138, in pip_version_check
    state.save(pypi_version, current_time)
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/utils/outdated.py", line 62, in save
    with lockfile.LockFile(self.statefile_path):
  File "/usr/local/lib/python3.7/site-packages/pip/_vendor/lockfile/__init__.py", line 197, in __enter__
    self.acquire()
  File "/usr/local/lib/python3.7/site-packages/pip/_vendor/lockfile/linklockfile.py", line 21, in acquire
    raise LockFailed("failed to create %s" % self.unique_name)
pip._vendor.lockfile.LockFailed: failed to create /Users/user/Library/Caches/pip/¯\_(ツ)_/¯-714d9300.40509451801170741664861
¯\_(ツ)_/¯:~ user$

Expected behavior

How to Reproduce

Set your machine's hostname to ¯\_(ツ)_/¯

1. Get package from '...'
2. Then run '...'
3. An error occurs.

Output

Paste the output of the steps above, including the commands themselves and
pip's output/traceback etc.

[cjdelisle]

FYI this is fixed by changing to a more normal hostname.

[chrahunt]

Hello! This will be fixed by #6954, since we will no longer use lockfile (or otherwise use the hostname) in this code path.