pip: pip freeze returns "Permission denied: 'hg'" after using pip install -e

Environment

• pip version: 19.3.1 and above
• Python version: 3.7.7
• OS: macOS 10.14.6

Description After using pip install -e to install a local package, pip freeze returns an error: PermissionError: [Errno 13] Permission denied: 'hg'.

I do not use Mercurial and do not have an hg executable on my machine.

It happens with pip 19.3.1 and above, when using -e.

It doesn’t happen with pip 19.2.3, and it doesn’t happen if I don’t use -e. It doesn’t happen with pip list.

Expected behavior pip freeze should return the list of packages.

How to Reproduce Create a simple package, install it using pip install -e, then run pip freeze. It works with pip 19.2.3 but in 19.3.1 or later versions, pip freeze returns an error.

You can just copy/paste the following, which creates a virtual environment and does the pip install -e and the pip freeze on two different versions of pip:

cd
mkdir testdir
cd testdir/
virtualenv testenv
source testenv/bin/activate
mkdir my_plugin
echo "
from setuptools import setup

setup(
    name='my_plugin',
    py_modules=['my_plugin'],
    version='1.0.0',
)
" > my_plugin/setup.py
pip install pip==19.2.3
pip -V
pip install -e my_plugin/
pip freeze
pip uninstall -y my_plugin
pip freeze
pip install pip==19.3.1
pip -V
pip install -e my_plugin/
pip freeze
pip uninstall -y my_plugin
pip freeze

Output Here’s the output of the above commands, starting at the first pip -V:

$ pip -V
pip 19.2.3 from /Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip (python 3.7)
$ pip install -e my_plugin/
Obtaining file:///Users/<username>/testdir/my_plugin
Installing collected packages: my-plugin
  Running setup.py develop for my-plugin
Successfully installed my-plugin
WARNING: You are using pip version 19.2.3, however version 20.2b1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
$ pip freeze
# Editable install with no version control (my-plugin==1.0.0)
-e /Users/<username>/testdir/my_plugin
$ pip uninstall -y my_plugin
Uninstalling my-plugin-1.0.0:
  Successfully uninstalled my-plugin-1.0.0
$ pip freeze
$ pip install pip==19.3.1
Collecting pip==19.3.1
  Using cached https://files.pythonhosted.org/packages/00/b6/9cfa56b4081ad13874b0c6f96af8ce16cfbc1cb06bedf8e9164ce5551ec1/pip-19.3.1-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 19.2.3
    Uninstalling pip-19.2.3:
      Successfully uninstalled pip-19.2.3
Successfully installed pip-19.3.1
$ pip -V
pip 19.3.1 from /Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip (python 3.7)
$ pip install -e my_plugin/
Obtaining file:///Users/<username>/testdir/my_plugin
Installing collected packages: my-plugin
  Running setup.py develop for my-plugin
Successfully installed my-plugin
WARNING: You are using pip version 19.3.1; however, version 20.1.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
$ pip freeze
ERROR: Exception:
Traceback (most recent call last):
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/cli/base_command.py", line 153, in _main
    status = self.run(options, args)
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/commands/freeze.py", line 100, in run
    for line in freeze(**freeze_kwargs):
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/operations/freeze.py", line 70, in freeze
    req = FrozenRequirement.from_dist(dist)
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/operations/freeze.py", line 249, in from_dist
    req, editable, comments = get_requirement_info(dist)
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/operations/freeze.py", line 188, in get_requirement_info
    vcs_backend = vcs.get_backend_for_dir(location)
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/vcs/versioncontrol.py", line 234, in get_backend_for_dir
    if vcs_backend.controls_location(location):
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/vcs/mercurial.py", line 149, in controls_location
    log_failed_cmd=False)
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/vcs/versioncontrol.py", line 632, in run_command
    log_failed_cmd=log_failed_cmd)
  File "/Users/<username>/testdir/testenv/lib/python3.7/site-packages/pip/_internal/utils/subprocess.py", line 190, in call_subprocess
    stdout=subprocess.PIPE, cwd=cwd, env=env,
  File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/subprocess.py", line 800, in __init__
    restore_signals, start_new_session)
  File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/subprocess.py", line 1551, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
PermissionError: [Errno 13] Permission denied: 'hg'
$ pip uninstall -y my_plugin
Uninstalling my-plugin-1.0.0:
  Successfully uninstalled my-plugin-1.0.0
$ pip freeze
$ 

pip list still works. In fact, if I add pip list just before the problematic pip freeze in the chain of commands above, there is no error:

$ pip list
Package    Version
---------- -------
my-plugin  1.0.0  
pip        19.3.1 
setuptools 47.1.1 
wheel      0.34.2 
WARNING: You are using pip version 19.3.1; however, version 20.1.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
$ pip freeze
my-plugin==1.0.0