pytest-virtualenv requires setuptools to install

In the goal of removing implicit dependencies on setuptools out of the tool chains, I've stumbled on an issue where pytest-virtualenv, by virtue of its dependency on termcolor, requires setuptools to install (even when installing using pip). That package does not have a wheel, does not define a pyproject.toml, and thus pip falls back to the implicit 'build with setuptools'.

To replicate, build a virtualenv without setuptools and then install the package:

python -m venv env
env/bin/pip uninstall -y setuptools
env/bin/pip install --no-cache-dir pytest-virtualenv

Collecting pytest-virtualenv
  Downloading https://files.pythonhosted.org/packages/21/7f/0ec1ab9b8fcd4a3a063b97143a97d1c093d01227353b682c9027d14b14c2/pytest_virtualenv-1.7.0-py2.py3-none-any.whl
Collecting virtualenv (from pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/05/f1/2e07e8ca50e047b9cc9ad56cf4291f4e041fa73207d000a095fe478abf84/virtualenv-16.7.9-py2.py3-none-any.whl (3.4MB)
     |████████████████████████████████| 3.4MB 2.0MB/s 
Collecting pytest (from pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/e6/94/29b5a09edc970a2f24742e6186dfe497cd6c778e60e54693215a36852613/pytest-5.3.3-py3-none-any.whl (235kB)
     |████████████████████████████████| 245kB 26.2MB/s 
Collecting pytest-fixture-config (from pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/83/6e/ebc4d3d5c51cc440bdb0adcd274ff2436dc6814ed1cc2cbc6d5386aaf85c/pytest_fixture_config-1.7.0-py2.py3-none-any.whl
Collecting pytest-shutil (from pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/26/b7/ef48a8f1f81ae4cd6f22992f6ffb7e9bf030d6e6654e2e626a05aaf5e880/pytest_shutil-1.7.0-py2.py3-none-any.whl
Collecting attrs>=17.4.0 (from pytest->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/a2/db/4313ab3be961f7a763066401fb77f7748373b6094076ae2bda2806988af6/attrs-19.3.0-py2.py3-none-any.whl
Collecting py>=1.5.0 (from pytest->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/99/8d/21e1767c009211a62a8e3067280bfce76e89c9f876180308515942304d2d/py-1.8.1-py2.py3-none-any.whl (83kB)
     |████████████████████████████████| 92kB 20.7MB/s 
Collecting more-itertools>=4.0.0 (from pytest->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/bc/e2/3206a70758a21f9878fcf9478282bb68fbc66a5564718f9ed724c3f2bb52/more_itertools-8.1.0-py3-none-any.whl (41kB)
     |████████████████████████████████| 51kB 67.3MB/s 
Collecting pluggy<1.0,>=0.12 (from pytest->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/a0/28/85c7aa31b80d150b772fbe4a229487bc6644da9ccb7e427dd8cc60cb8a62/pluggy-0.13.1-py2.py3-none-any.whl
Collecting wcwidth (from pytest->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/58/b4/4850a0ccc6f567cc0ebe7060d20ffd4258b8210efadc259da62dc6ed9c65/wcwidth-0.1.8-py2.py3-none-any.whl
Collecting packaging (from pytest->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/d8/5b/3098db49a61ccc8583ffead6aedc226f08ff56dc03106b6ec54451e27a30/packaging-20.0-py2.py3-none-any.whl
Collecting execnet (from pytest-shutil->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/d3/2e/c63af07fa471e0a02d05793c7a56a9f7d274a8489442a5dc4fb3b2b3c705/execnet-1.7.1-py2.py3-none-any.whl
Collecting contextlib2 (from pytest-shutil->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/85/60/370352f7ef6aa96c52fb001831622f50f923c1d575427d021b8ab3311236/contextlib2-0.6.0.post1-py2.py3-none-any.whl
Collecting termcolor (from pytest-shutil->pytest-virtualenv)
  Downloading https://files.pythonhosted.org/packages/8a/48/a76be51647d0eb9f10e2a4511bf3ffb8cc1e6b14e9e4fab46173aa79f981/termcolor-1.1.0.tar.gz
    ERROR: Command errored out with exit status 1:
     command: /Users/jaraco/code/public/pypa/setuptools/env/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/private/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/pip-install-nsnw5epl/termcolor/setup.py'"'"'; __file__='"'"'/private/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/pip-install-nsnw5epl/termcolor/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base pip-egg-info
         cwd: /private/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/pip-install-nsnw5epl/termcolor/
    Complete output (3 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    ModuleNotFoundError: No module named 'setuptools'
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

Start by reproducing the failure with the documented virtualenv and pip commands, then inspect pytest-shutil/setup.py and the termcolor installation path. Confirm which dependency metadata causes the setuptools requirement. Done means pytest-virtualenv installs successfully in an environment where setuptools has been removed.