tox: use isolated build

Add pypoject.toml specifying the actual build dependencies. Update
setup.py with similar requirements.

Signed-off-by: Robin Jarry <[email protected]>

Author: rjarry

pyproject.toml

@@ -0,0 +1,8 @@
+[build-system]
+requires = [
+    # The minimum setuptools version is specific to the PEP 517 backend,
+    # and may be stricter than the version required in `setup.py`
+    "setuptools>=40.6.0",
+    "cffi; platform_python_implementation != 'PyPy'",
+]
+build-backend = "setuptools.build_meta"

setup.py

@@ -6,19 +6,10 @@
 import os
 import re
 import subprocess
-import sys
 
 import setuptools
 
 
-CFFI_REQ = 'cffi>=1.7,!=1.11.3'
-INSTALL_REQS = []
-SETUP_REQS = []
-if '_cffi_backend' not in sys.builtin_module_names:
-    INSTALL_REQS.append(CFFI_REQ)
-    SETUP_REQS.append(CFFI_REQ)
-
-
 #------------------------------------------------------------------------------
 if os.environ.get('LIBYANG_INSTALL', 'system') == 'embed':
     raise NotImplementedError(
@@ -126,8 +117,13 @@ def _version():
     zip_safe=False,
     include_package_data=True,
     python_requires='>=3.5',
-    setup_requires=SETUP_REQS,
-    install_requires=INSTALL_REQS,
+    setup_requires=[
+        'setuptools',
+        'cffi; platform_python_implementation != "PyPy"',
+    ],
+    install_requires=[
+        'cffi; platform_python_implementation != "PyPy"',
+    ],
     cffi_modules=['cffi/build.py:BUILDER'],
     cmdclass={
     },

tox.ini

@@ -1,6 +1,11 @@
 [tox]
 envlist = lint,py{35,36,37,38,py3},py3-{master,devel}
 skip_missing_interpreters = true
+isolated_build = true
+distdir = {toxinidir}/dist
+
+[tox:.package]
+basepython = python3
 
 [testenv]
 description = Compile extension and run tests against {envname}.