Weird pip behaviour when installing package in editable mode with sys.exit inside setup.py after PEP 517

[kprzybyla]

Environment

• pip version: 19.0.3 (also present in 19.1.1)
• Python version: 3.7.3
• OS: ArcoLinux (Arch)

Description

After adding pyproject.toml (even an empty one) to my project I noticed that installation of my project in editable mode with pip started to fail. After some investigation it turned out that having sys.exit inside setup.py causes the problem.

Expected behavior

Executing everything from reproduce steps should not raise an error or if this behavior is indeed intended, better describe the issue.

How to Reproduce

1. Create new project directory
2. Create pyproject.toml inside the project directory with any content (even empty)
3. Create setup.py inside the project directory with following content:

import sys

from setuptools import setup

def main():
    setup()

if __name__ == '__main__':
    sys.exit(main())

4. Execute pip install -e . inside the project directory

Workaround

Removing sys.exit from main entry point resolves the issue:

from setuptools import setup

def main():
    setup()

if __name__ == '__main__':
    main()

Output

Running command /home/krprzyby/PycharmProjects/pep517/venv/bin/python /home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_vendor/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmpjpen2vq1
  running egg_info
  creating UNKNOWN.egg-info
  writing UNKNOWN.egg-info/PKG-INFO
  writing dependency_links to UNKNOWN.egg-info/dependency_links.txt
  writing top-level names to UNKNOWN.egg-info/top_level.txt
  writing manifest file 'UNKNOWN.egg-info/SOURCES.txt'
  reading manifest file 'UNKNOWN.egg-info/SOURCES.txt'
  writing manifest file 'UNKNOWN.egg-info/SOURCES.txt'
  Getting requirements to build wheel ... done
ERROR: Could not install packages due to an EnvironmentError.
Traceback (most recent call last):
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/commands/install.py", line 352, in run
    resolver.resolve(requirement_set)
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/resolve.py", line 131, in resolve
    self._resolve_one(requirement_set, req)
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/resolve.py", line 294, in _resolve_one
    abstract_dist = self._get_abstract_dist_for(req_to_install)
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/resolve.py", line 226, in _get_abstract_dist_for
    req, self.require_hashes, self.use_user_site, self.finder,
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/operations/prepare.py", line 395, in prepare_editable_requirement
    abstract_dist.prep_for_dist(finder, self.build_isolation)
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/operations/prepare.py", line 169, in prep_for_dist
    self.install_backend_dependencies(finder=finder)
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_internal/operations/prepare.py", line 123, in install_backend_dependencies
    reqs = req.pep517_backend.get_requires_for_build_wheel()
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_vendor/pep517/wrappers.py", line 71, in get_requires_for_build_wheel
    'config_settings': config_settings
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_vendor/pep517/wrappers.py", line 158, in _call_hook
    data = compat.read_json(pjoin(td, 'output.json'))
  File "/home/krprzyby/PycharmProjects/pep517/venv/lib/python3.7/site-packages/pip/_vendor/pep517/compat.py", line 12, in read_json
    with open(path, 'r', encoding='utf-8') as f:
FileNotFoundError: [Errno 2] No such file or directory: '/tmp/tmpjpen2vq1/output.json'

[chrahunt]

Prior to PEP 517, pip was directly invoking setup.py. Now we delegate to setuptools.build_meta. If we expect the provided setup.py to work as it does with the legacy behavior (and when running with --no-use-pep517) then we should make an issue on the setuptools bug tracker.

We should still be behaving better than this. I think it will require some changes in pep517 to catch and report errors in a way we can use (related to pypa/pyproject-hooks#10), then we will need to make sure to interpret the error and output it in a way that indicates the issue is related to the backend/user configuration.

[con-f-use]

Related issue: #6370 the "fix" is in pip 19.1.1.

Btw. does someone know why pip 19.1.1 is a release on github, but not available on pypi yet? (nevermind, I was too stupid to use the search "19.11" is not a thing)

[pradyunsg]

pip 19.1.1 has been released on PyPI.

https://pypi.org/project/pip/19.1.1/