--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/python3.8/site-packages/pip/_vendor/pep517/wrappers.py	Mon Jul 27 03:47:31 2020 -0400
@@ -0,0 +1,298 @@
+import threading
+from contextlib import contextmanager
+import os
+from os.path import dirname, abspath, join as pjoin
+import shutil
+from subprocess import check_call, check_output, STDOUT
+import sys
+from tempfile import mkdtemp
+
+from . import compat
+
+_in_proc_script = pjoin(dirname(abspath(__file__)), '_in_process.py')
+
+
+@contextmanager
+def tempdir():
+    td = mkdtemp()
+    try:
+        yield td
+    finally:
+        shutil.rmtree(td)
+
+
+class BackendUnavailable(Exception):
+    """Will be raised if the backend cannot be imported in the hook process."""
+    def __init__(self, traceback):
+        self.traceback = traceback
+
+
+class BackendInvalid(Exception):
+    """Will be raised if the backend is invalid."""
+    def __init__(self, backend_name, backend_path, message):
+        self.backend_name = backend_name
+        self.backend_path = backend_path
+        self.message = message
+
+
+class HookMissing(Exception):
+    """Will be raised on missing hooks."""
+    def __init__(self, hook_name):
+        super(HookMissing, self).__init__(hook_name)
+        self.hook_name = hook_name
+
+
+class UnsupportedOperation(Exception):
+    """May be raised by build_sdist if the backend indicates that it can't."""
+    def __init__(self, traceback):
+        self.traceback = traceback
+
+
+def default_subprocess_runner(cmd, cwd=None, extra_environ=None):
+    """The default method of calling the wrapper subprocess."""
+    env = os.environ.copy()
+    if extra_environ:
+        env.update(extra_environ)
+
+    check_call(cmd, cwd=cwd, env=env)
+
+
+def quiet_subprocess_runner(cmd, cwd=None, extra_environ=None):
+    """A method of calling the wrapper subprocess while suppressing output."""
+    env = os.environ.copy()
+    if extra_environ:
+        env.update(extra_environ)
+
+    check_output(cmd, cwd=cwd, env=env, stderr=STDOUT)
+
+
+def norm_and_check(source_tree, requested):
+    """Normalise and check a backend path.
+
+    Ensure that the requested backend path is specified as a relative path,
+    and resolves to a location under the given source tree.
+
+    Return an absolute version of the requested path.
+    """
+    if os.path.isabs(requested):
+        raise ValueError("paths must be relative")
+
+    abs_source = os.path.abspath(source_tree)
+    abs_requested = os.path.normpath(os.path.join(abs_source, requested))
+    # We have to use commonprefix for Python 2.7 compatibility. So we
+    # normalise case to avoid problems because commonprefix is a character
+    # based comparison :-(
+    norm_source = os.path.normcase(abs_source)
+    norm_requested = os.path.normcase(abs_requested)
+    if os.path.commonprefix([norm_source, norm_requested]) != norm_source:
+        raise ValueError("paths must be inside source tree")
+
+    return abs_requested
+
+
+class Pep517HookCaller(object):
+    """A wrapper around a source directory to be built with a PEP 517 backend.
+
+    source_dir : The path to the source directory, containing pyproject.toml.
+    build_backend : The build backend spec, as per PEP 517, from
+        pyproject.toml.
+    backend_path : The backend path, as per PEP 517, from pyproject.toml.
+    runner : A callable that invokes the wrapper subprocess.
+
+    The 'runner', if provided, must expect the following:
+        cmd : a list of strings representing the command and arguments to
+            execute, as would be passed to e.g. 'subprocess.check_call'.
+        cwd : a string representing the working directory that must be
+            used for the subprocess. Corresponds to the provided source_dir.
+        extra_environ : a dict mapping environment variable names to values
+            which must be set for the subprocess execution.
+    """
+    def __init__(
+            self,
+            source_dir,
+            build_backend,
+            backend_path=None,
+            runner=None,
+    ):
+        if runner is None:
+            runner = default_subprocess_runner
+
+        self.source_dir = abspath(source_dir)
+        self.build_backend = build_backend
+        if backend_path:
+            backend_path = [
+                norm_and_check(self.source_dir, p) for p in backend_path
+            ]
+        self.backend_path = backend_path
+        self._subprocess_runner = runner
+
+    # TODO: Is this over-engineered? Maybe frontends only need to
+    #       set this when creating the wrapper, not on every call.
+    @contextmanager
+    def subprocess_runner(self, runner):
+        """A context manager for temporarily overriding the default subprocess
+        runner.
+        """
+        prev = self._subprocess_runner
+        self._subprocess_runner = runner
+        yield
+        self._subprocess_runner = prev
+
+    def get_requires_for_build_wheel(self, config_settings=None):
+        """Identify packages required for building a wheel
+
+        Returns a list of dependency specifications, e.g.:
+            ["wheel >= 0.25", "setuptools"]
+
+        This does not include requirements specified in pyproject.toml.
+        It returns the result of calling the equivalently named hook in a
+        subprocess.
+        """
+        return self._call_hook('get_requires_for_build_wheel', {
+            'config_settings': config_settings
+        })
+
+    def prepare_metadata_for_build_wheel(
+            self, metadata_directory, config_settings=None,
+            _allow_fallback=True):
+        """Prepare a *.dist-info folder with metadata for this project.
+
+        Returns the name of the newly created folder.
+
+        If the build backend defines a hook with this name, it will be called
+        in a subprocess. If not, the backend will be asked to build a wheel,
+        and the dist-info extracted from that (unless _allow_fallback is
+        False).
+        """
+        return self._call_hook('prepare_metadata_for_build_wheel', {
+            'metadata_directory': abspath(metadata_directory),
+            'config_settings': config_settings,
+            '_allow_fallback': _allow_fallback,
+        })
+
+    def build_wheel(
+            self, wheel_directory, config_settings=None,
+            metadata_directory=None):
+        """Build a wheel from this project.
+
+        Returns the name of the newly created file.
+
+        In general, this will call the 'build_wheel' hook in the backend.
+        However, if that was previously called by
+        'prepare_metadata_for_build_wheel', and the same metadata_directory is
+        used, the previously built wheel will be copied to wheel_directory.
+        """
+        if metadata_directory is not None:
+            metadata_directory = abspath(metadata_directory)
+        return self._call_hook('build_wheel', {
+            'wheel_directory': abspath(wheel_directory),
+            'config_settings': config_settings,
+            'metadata_directory': metadata_directory,
+        })
+
+    def get_requires_for_build_sdist(self, config_settings=None):
+        """Identify packages required for building a wheel
+
+        Returns a list of dependency specifications, e.g.:
+            ["setuptools >= 26"]
+
+        This does not include requirements specified in pyproject.toml.
+        It returns the result of calling the equivalently named hook in a
+        subprocess.
+        """
+        return self._call_hook('get_requires_for_build_sdist', {
+            'config_settings': config_settings
+        })
+
+    def build_sdist(self, sdist_directory, config_settings=None):
+        """Build an sdist from this project.
+
+        Returns the name of the newly created file.
+
+        This calls the 'build_sdist' backend hook in a subprocess.
+        """
+        return self._call_hook('build_sdist', {
+            'sdist_directory': abspath(sdist_directory),
+            'config_settings': config_settings,
+        })
+
+    def _call_hook(self, hook_name, kwargs):
+        # On Python 2, pytoml returns Unicode values (which is correct) but the
+        # environment passed to check_call needs to contain string values. We
+        # convert here by encoding using ASCII (the backend can only contain
+        # letters, digits and _, . and : characters, and will be used as a
+        # Python identifier, so non-ASCII content is wrong on Python 2 in
+        # any case).
+        # For backend_path, we use sys.getfilesystemencoding.
+        if sys.version_info[0] == 2:
+            build_backend = self.build_backend.encode('ASCII')
+        else:
+            build_backend = self.build_backend
+        extra_environ = {'PEP517_BUILD_BACKEND': build_backend}
+
+        if self.backend_path:
+            backend_path = os.pathsep.join(self.backend_path)
+            if sys.version_info[0] == 2:
+                backend_path = backend_path.encode(sys.getfilesystemencoding())
+            extra_environ['PEP517_BACKEND_PATH'] = backend_path
+
+        with tempdir() as td:
+            hook_input = {'kwargs': kwargs}
+            compat.write_json(hook_input, pjoin(td, 'input.json'),
+                              indent=2)
+
+            # Run the hook in a subprocess
+            self._subprocess_runner(
+                [sys.executable, _in_proc_script, hook_name, td],
+                cwd=self.source_dir,
+                extra_environ=extra_environ
+            )
+
+            data = compat.read_json(pjoin(td, 'output.json'))
+            if data.get('unsupported'):
+                raise UnsupportedOperation(data.get('traceback', ''))
+            if data.get('no_backend'):
+                raise BackendUnavailable(data.get('traceback', ''))
+            if data.get('backend_invalid'):
+                raise BackendInvalid(
+                    backend_name=self.build_backend,
+                    backend_path=self.backend_path,
+                    message=data.get('backend_error', '')
+                )
+            if data.get('hook_missing'):
+                raise HookMissing(hook_name)
+            return data['return_val']
+
+
+class LoggerWrapper(threading.Thread):
+    """
+    Read messages from a pipe and redirect them
+    to a logger (see python's logging module).
+    """
+
+    def __init__(self, logger, level):
+        threading.Thread.__init__(self)
+        self.daemon = True
+
+        self.logger = logger
+        self.level = level
+
+        # create the pipe and reader
+        self.fd_read, self.fd_write = os.pipe()
+        self.reader = os.fdopen(self.fd_read)
+
+        self.start()
+
+    def fileno(self):
+        return self.fd_write
+
+    @staticmethod
+    def remove_newline(msg):
+        return msg[:-1] if msg.endswith(os.linesep) else msg
+
+    def run(self):
+        for line in self.reader:
+            self._write(self.remove_newline(line))
+
+    def _write(self, message):
+        self.logger.log(self.level, message)