Build dependencies with no binary wheels don't work

[pv]

• Pip version: 10.0.0
• Python version: 3.6.5
• Operating system: Linux/Fedora

Description:

When installing dependencies given in pyproject.toml, pip does not seem to consider sdists on Pypi, only binary wheels.

That it only looks for binary wheels is not immediately expected, and does not seem to be mentioned in PEP 518. I think the correct behavior is that sdists are considered (although perhaps only if there are no binary wheels available).

What I've run:

The following is a reproducing shell script

# test.sh
set -e -x

rm -rf mytest
mkdir mytest
cd mytest

python3 -mvenv env
./env/bin/pip install --upgrade 'pip>=10'

echo "assert False" > setup.py
cat <<EOF > pyproject.toml
[build-system]
requires = [
    "wheel",
    "setuptools",
    "numpy==1.8.2",
]
EOF

./env/bin/pip wheel .

When I run this, I get

+ rm -rf mytest
+ mkdir mytest
+ cd mytest
+ python3 -mvenv env
+ ./env/bin/pip install --upgrade 'pip>=10'
Collecting pip>=10
  Using cached pip-10.0.0-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 9.0.3
    Uninstalling pip-9.0.3:
      Successfully uninstalled pip-9.0.3
Successfully installed pip-10.0.0
+ echo 'assert False'
+ cat
+ ./env/bin/pip wheel .
Processing /home/pauli/tmp/foo/mytest
  Could not find a version that satisfies the requirement numpy==1.8.2 (from versions: 1.11.3, 1.12.0rc2, 1.12.0, 1.12.1rc1, 1.12.1, 1.13.0rc1, 1.13.0rc2, 1.13.0, 1.13.1, 1.13.3, 1.14.0rc1, 1.14.0, 1.14.1, 1.14.2)
No matching distribution found for numpy==1.8.2

I would have expected this would succeed in installing the build dependencies. (And fail when it tries to run the setup.py --- in my real use I of course have a working setup.py but the behavior is the same).

If the version number is changed to e.g. numpy==1.11.3 for which Numpy has binary wheels on PyPi, it works as expected.

[pradyunsg]

Hey @pv!

This is a known limitation of the current implementation of PEP 518 in pip 10 -- see https://pip.pypa.io/en/stable/reference/pip/#pep-518-support.

[pv]

I only looked if you had open issues about the problem, and did not find such issues on this tracker.

[jorisvandenbossche]

Would it somehow be possible for pip to fall back to the "old" way (as if there would be no pyproject.toml file present) if this is failing? Because now this also makes that you cannot install with pip on platforms for which no wheels are available.

[pradyunsg]

Yes. Just pass the --no-build-isolation option.

[jorisvandenbossche]

I actually was wondering if pip could do this automatically (given the limited support for pyproject.toml), but I suppose from the point of view of pip you will say that this is the responsibility of the user to specify it?

[rahulwa]

How can I pass --no-build-isolation option through the environment variable? I tried like below but it did not work.
PIP_NO_BUILD_ISOLATION=true pip install pandas

[pfmoore]

Try PIP_NO_BUILD_ISOLATION=false. The way boolean flags are handled is a bit weird.