Adding PEP 518 test

cibuildwheel/windows.py

@@ -5,6 +5,7 @@ import sys
 import tempfile
 from glob import glob
 from zipfile import ZipFile
+import toml
 
 from typing import Dict, List, Optional, NamedTuple
 
@@ -148,6 +149,24 @@ def setup_python(python_configuration: PythonConfiguration, dependency_constrain
     shell(['pip', '--version'], env=env)
     shell(['pip', 'install', '--upgrade', 'setuptools', 'wheel'] + dependency_constraint_flags, env=env)
 
+    # Python 3.5 PEP 518 hack (see https://github.com/pypa/pip/issues/8392#issuecomment-639563494)
+    # Basically, nuget's Python is an embedded Python distribution, which is not supported by pip.
+    # Before version 3.6, there was no way to disable the "embedded" behavior, including the ignoring
+    # of environment variables, including the ones pip uses to setup PEP 518 builds.
+    #
+    # The fix here is as suggested in that issue; we manually setup the PEP 518 requirements. Since we
+    # are in a fresh environment (except for pinned cibuildweel dependencies), the build is already
+    # mostly "isolated".
+    if python_configuration.version.startswith('3.5') and os.path.exists('pyproject.toml'):
+        data = toml.load('pyproject.toml')
+        requirements = (
+            data['build-system'].get('requires', [])
+            if 'build-system' in data
+            else []
+        )
+        if requirements:
+            shell(['pip', 'install'] + requirements + dependency_constraint_flags, env=env)
+
     return env
 
 

setup.py

@@ -14,7 +14,7 @@ with io.open(os.path.join(this_directory, 'README.md'), encoding='utf-8') as f:
 setup(
     name='cibuildwheel',
     version='1.4.2',
-    install_requires=['bashlex!=0.13'],
+    install_requires=['bashlex!=0.13', 'toml'],
     description="Build Python wheels on CI with minimal configuration.",
     long_description=long_description,
     long_description_content_type='text/markdown',

test/test_pep518.py

@@ -0,0 +1,44 @@
+import textwrap
+from . import test_projects
+from . import utils
+
+basic_project = test_projects.new_c_project(
+    setup_py_add=textwrap.dedent(
+        """
+        # Will fail if PEP 518 does work
+        import requests
+        assert requests.__version__ == "2.23.0", "Requests found but wrong version ({0})".format(requests.__version__)
+
+        # Just making sure environment is still set
+        import os
+        if os.environ.get("CIBUILDWHEEL", "0") != "1":
+            raise Exception("CIBUILDWHEEL environment variable is not set to 1")
+        """
+    )
+)
+
+basic_project.files[
+    "pyproject.toml"
+] = """
+[build-system]
+requires = [
+    "setuptools>=42",
+    "wheel",
+    "requests==2.23.0"
+]
+
+build-backend = "setuptools.build_meta"
+"""
+
+
+def test_pep518(tmp_path):
+
+    project_dir = tmp_path / "project"
+    basic_project.generate(project_dir)
+
+    # build the wheels
+    actual_wheels = utils.cibuildwheel_run(project_dir)
+
+    # check that the expected wheels are produced
+    expected_wheels = utils.expected_wheels("spam", "0.1.0")
+    assert set(actual_wheels) == set(expected_wheels)