Upgrading pip fails on Windows when install path is too long

Received the following log on https://github.com/Microsoft/PTVS/issues/782.

Virtual environment is being created at 'C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env'
Virtual environment was successfully created at 'C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env'
----- Installing 'pip' -----
You are using pip version 6.0.8, however version 7.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
Collecting pip from https://pypi.python.org/packages/py2.py3/p/pip/pip-7.1.2-py2.py3-none-any.whl#md5=5ff9fec0be479e4e36df467556deed4d
  Using cached pip-7.1.2-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 6.0.8
    Uninstalling pip-6.0.8:
      Exception:
      Traceback (most recent call last):
        File "C:\Python34\lib\shutil.py", line 523, in move
          os.rename(src, real_dst)
      FileNotFoundError: [WinError 3] The system cannot find the path specified: 'c:\\users\\trevorsullivan\\source\\repos\\pythonapplication11\\pythonapplication11\\env\\lib\\site-packages\\pip\\_vendor\\requests\\packages\\urllib3\\packages\\ssl_match_hostname\\__pycache__\\_implementation.cpython-34.pyc' -> 'C:\\Users\\TREVOR~1\\AppData\\Local\\Temp\\pip-h64zdfhc-uninstall\\users\\trevorsullivan\\source\\repos\\pythonapplication11\\pythonapplication11\\env\\lib\\site-packages\\pip\\_vendor\\requests\\packages\\urllib3\\packages\\ssl_match_hostname\\__pycache__\\_implementation.cpython-34.pyc'

      During handling of the above exception, another exception occurred:

      Traceback (most recent call last):
        File "C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env\lib\site-packages\pip\basecommand.py", line 232, in main
          status = self.run(options, args)
        File "C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env\lib\site-packages\pip\commands\install.py", line 347, in run
          root=options.root_path,
        File "C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env\lib\site-packages\pip\req\req_set.py", line 543, in install
          requirement.uninstall(auto_confirm=True)
        File "C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env\lib\site-packages\pip\req\req_install.py", line 667, in uninstall
          paths_to_remove.remove(auto_confirm)
        File "C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env\lib\site-packages\pip\req\req_uninstall.py", line 126, in remove
          renames(path, new_path)
        File "C:\Users\TrevorSullivan\Source\Repos\PythonApplication11\PythonApplication11\env\lib\site-packages\pip\utils\__init__.py", line 316, in renames
          shutil.move(old, new)
        File "C:\Python34\lib\shutil.py", line 535, in move
          copy2(src, real_dst)
        File "C:\Python34\lib\shutil.py", line 245, in copy2
          copyfile(src, dst, follow_symlinks=follow_symlinks)
        File "C:\Python34\lib\shutil.py", line 109, in copyfile
          with open(dst, 'wb') as fdst:
      FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Users\\TREVOR~1\\AppData\\Local\\Temp\\pip-h64zdfhc-uninstall\\users\\trevorsullivan\\source\\repos\\pythonapplication11\\pythonapplication11\\env\\lib\\site-packages\\pip\\_vendor\\requests\\packages\\urllib3\\packages\\ssl_match_hostname\\__pycache__\\_implementation.cpython-34.pyc'
----- Failed to install 'pip' -----

The problem seems to be that the entire install path is replicated beneath TEMP, which very quickly exceeds the maximum path length supported by Windows. I guess the aim is to be able to rollback a failed uninstall (which also fails here, and leaves corrupt state), but we may need an alternative to including the full path - maybe generate some sort of map file as well?

[zooba]

I wouldn’t suggest going down the subst or mklink routes at all. pip should just name its temp directory something other than the full path to the eventual/original install location.

The fix in Python 3.6 and Windows 10 is fine, but will never apply to all users.

[dstufft]

Seems reasonable to me, I’d just say we should use a name that isn’t importable as well.