--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/python3.8/site-packages/pip/_vendor/pep517/envbuild.py	Mon Jul 27 03:47:31 2020 -0400
@@ -0,0 +1,167 @@
+"""Build wheels/sdists by installing build deps to a temporary environment.
+"""
+
+import os
+import logging
+import toml
+import shutil
+from subprocess import check_call
+import sys
+from sysconfig import get_paths
+from tempfile import mkdtemp
+
+from .wrappers import Pep517HookCaller, LoggerWrapper
+
+log = logging.getLogger(__name__)
+
+
+def _load_pyproject(source_dir):
+    with open(os.path.join(source_dir, 'pyproject.toml')) as f:
+        pyproject_data = toml.load(f)
+    buildsys = pyproject_data['build-system']
+    return (
+        buildsys['requires'],
+        buildsys['build-backend'],
+        buildsys.get('backend-path'),
+    )
+
+
+class BuildEnvironment(object):
+    """Context manager to install build deps in a simple temporary environment
+
+    Based on code I wrote for pip, which is MIT licensed.
+    """
+    # Copyright (c) 2008-2016 The pip developers (see AUTHORS.txt file)
+    #
+    # Permission is hereby granted, free of charge, to any person obtaining
+    # a copy of this software and associated documentation files (the
+    # "Software"), to deal in the Software without restriction, including
+    # without limitation the rights to use, copy, modify, merge, publish,
+    # distribute, sublicense, and/or sell copies of the Software, and to
+    # permit persons to whom the Software is furnished to do so, subject to
+    # the following conditions:
+    #
+    # The above copyright notice and this permission notice shall be
+    # included in all copies or substantial portions of the Software.
+    #
+    # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    # EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    # MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    # NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+    # LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+    # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+    # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+    path = None
+
+    def __init__(self, cleanup=True):
+        self._cleanup = cleanup
+
+    def __enter__(self):
+        self.path = mkdtemp(prefix='pep517-build-env-')
+        log.info('Temporary build environment: %s', self.path)
+
+        self.save_path = os.environ.get('PATH', None)
+        self.save_pythonpath = os.environ.get('PYTHONPATH', None)
+
+        install_scheme = 'nt' if (os.name == 'nt') else 'posix_prefix'
+        install_dirs = get_paths(install_scheme, vars={
+            'base': self.path,
+            'platbase': self.path,
+        })
+
+        scripts = install_dirs['scripts']
+        if self.save_path:
+            os.environ['PATH'] = scripts + os.pathsep + self.save_path
+        else:
+            os.environ['PATH'] = scripts + os.pathsep + os.defpath
+
+        if install_dirs['purelib'] == install_dirs['platlib']:
+            lib_dirs = install_dirs['purelib']
+        else:
+            lib_dirs = install_dirs['purelib'] + os.pathsep + \
+                install_dirs['platlib']
+        if self.save_pythonpath:
+            os.environ['PYTHONPATH'] = lib_dirs + os.pathsep + \
+                self.save_pythonpath
+        else:
+            os.environ['PYTHONPATH'] = lib_dirs
+
+        return self
+
+    def pip_install(self, reqs):
+        """Install dependencies into this env by calling pip in a subprocess"""
+        if not reqs:
+            return
+        log.info('Calling pip to install %s', reqs)
+        cmd = [
+            sys.executable, '-m', 'pip', 'install', '--ignore-installed',
+            '--prefix', self.path] + list(reqs)
+        check_call(
+            cmd,
+            stdout=LoggerWrapper(log, logging.INFO),
+            stderr=LoggerWrapper(log, logging.ERROR),
+        )
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        needs_cleanup = (
+            self._cleanup and
+            self.path is not None and
+            os.path.isdir(self.path)
+        )
+        if needs_cleanup:
+            shutil.rmtree(self.path)
+
+        if self.save_path is None:
+            os.environ.pop('PATH', None)
+        else:
+            os.environ['PATH'] = self.save_path
+
+        if self.save_pythonpath is None:
+            os.environ.pop('PYTHONPATH', None)
+        else:
+            os.environ['PYTHONPATH'] = self.save_pythonpath
+
+
+def build_wheel(source_dir, wheel_dir, config_settings=None):
+    """Build a wheel from a source directory using PEP 517 hooks.
+
+    :param str source_dir: Source directory containing pyproject.toml
+    :param str wheel_dir: Target directory to create wheel in
+    :param dict config_settings: Options to pass to build backend
+
+    This is a blocking function which will run pip in a subprocess to install
+    build requirements.
+    """
+    if config_settings is None:
+        config_settings = {}
+    requires, backend, backend_path = _load_pyproject(source_dir)
+    hooks = Pep517HookCaller(source_dir, backend, backend_path)
+
+    with BuildEnvironment() as env:
+        env.pip_install(requires)
+        reqs = hooks.get_requires_for_build_wheel(config_settings)
+        env.pip_install(reqs)
+        return hooks.build_wheel(wheel_dir, config_settings)
+
+
+def build_sdist(source_dir, sdist_dir, config_settings=None):
+    """Build an sdist from a source directory using PEP 517 hooks.
+
+    :param str source_dir: Source directory containing pyproject.toml
+    :param str sdist_dir: Target directory to place sdist in
+    :param dict config_settings: Options to pass to build backend
+
+    This is a blocking function which will run pip in a subprocess to install
+    build requirements.
+    """
+    if config_settings is None:
+        config_settings = {}
+    requires, backend, backend_path = _load_pyproject(source_dir)
+    hooks = Pep517HookCaller(source_dir, backend, backend_path)
+
+    with BuildEnvironment() as env:
+        env.pip_install(requires)
+        reqs = hooks.get_requires_for_build_sdist(config_settings)
+        env.pip_install(reqs)
+        return hooks.build_sdist(sdist_dir, config_settings)