PyPy 7.3.7 & MacOS 11.x: Numpy fails to build, but only as a build dependency when `--use-pep517` is active.

Description

Under PyPy 7.3.7, Numpy can be built and installed from source with pip install numpy, but it fails to build when being used as a PEP 517 build dependency, with an assertion error about an unsupported tag ('pp37', 'pypy37_pp73', 'macosx_10_7_x86_64').

However, it does appear to work with the --no-use-pep517 flag (at least, it proceeds beyond Numpy and fails anyway because Cython is not available).

Expected behavior

I expected Numpy to work as a PEP 517 build dependency, because it works when I install it as a regular dependency

pip version

pip 21.3.1

Python version

PyPy 7.3.7 (3.7)

OS

MacOS 11.6.1

How to Reproduce

/usr/local/bin/pypy3 --version
# Python 3.7.12 (44db26267d0a38e51a7e8490983ed7e7bcb84b74, Oct 28 2021, 05:11:03)
# [PyPy 7.3.7 with GCC Apple LLVM 13.0.0 (clang-1300.0.29.3)]

/usr/local/bin/pypy3 -m venv ./my-project
./my-project/bin/python -m pip install -U pip setuptools wheel

This works fine:

./my-project/bin/python -m pip install numpy

This does not:

./my-project/bin/python -m pip install -U scipy

But this works fine (until it hits the unrelated Cython error):

./my-project/bin/python -m pip install --no-use-pep517 -U scipy

Output

< ... huge build log and traceback ... >

    AssertionError: would build wheel with unsupported tag ('pp37', 'pypy37_pp73', 'macosx_10_7_x86_64')
    ----------------------------------------
    ERROR: Failed building wheel for numpy
  Failed to build numpy
  ERROR: Could not build wheels for numpy, which is required to install pyproject.toml-based projects
  ----------------------------------------

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

The tag pp37-pypy37_pp73-macosx_10_7_x86_64 is listed in the previously attached pip debug output, so that tag is fine from pip’s perspective. It’s likely a bug in wheel; the would build wheel with unsupported tag was emitted by it.

[fievelk]

Slightly OT. I was having a similar issue, but it was unrelated to the --use-pep517: I couldn’t install numpy on macOS 12.2.1 Monterey, not even with a simple pip install numpy. My configuration:

> python --version
Python 3.8.12 (9ef55f6fc369, Oct 25 2021, 05:10:01)
[PyPy 7.3.7 with GCC Apple LLVM 13.0.0 (clang-1300.0.29.3)]

And the final output error was the same:

Failed to build numpy ERROR: Could not build wheels for numpy, which is required to install pyproject.toml-based projects

I first ran brew doctor, which showed that my Command Line Tools (XCode) were outdated. Then I just followed the instructions to update them:

sudo rm -rf /Library/Developer/CommandLineTools
sudo xcode-select --install

This solved the issue.

I hope this might help others that get here looking for a solution.