--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/python3.8/site-packages/pip/_internal/distributions/sdist.py	Mon Jul 27 03:47:31 2020 -0400
@@ -0,0 +1,104 @@
+import logging
+
+from pip._internal.build_env import BuildEnvironment
+from pip._internal.distributions.base import AbstractDistribution
+from pip._internal.exceptions import InstallationError
+from pip._internal.utils.subprocess import runner_with_spinner_message
+from pip._internal.utils.typing import MYPY_CHECK_RUNNING
+
+if MYPY_CHECK_RUNNING:
+    from typing import Set, Tuple
+
+    from pip._vendor.pkg_resources import Distribution
+    from pip._internal.index.package_finder import PackageFinder
+
+
+logger = logging.getLogger(__name__)
+
+
+class SourceDistribution(AbstractDistribution):
+    """Represents a source distribution.
+
+    The preparation step for these needs metadata for the packages to be
+    generated, either using PEP 517 or using the legacy `setup.py egg_info`.
+    """
+
+    def get_pkg_resources_distribution(self):
+        # type: () -> Distribution
+        return self.req.get_dist()
+
+    def prepare_distribution_metadata(self, finder, build_isolation):
+        # type: (PackageFinder, bool) -> None
+        # Load pyproject.toml, to determine whether PEP 517 is to be used
+        self.req.load_pyproject_toml()
+
+        # Set up the build isolation, if this requirement should be isolated
+        should_isolate = self.req.use_pep517 and build_isolation
+        if should_isolate:
+            self._setup_isolation(finder)
+
+        self.req.prepare_metadata()
+
+    def _setup_isolation(self, finder):
+        # type: (PackageFinder) -> None
+        def _raise_conflicts(conflicting_with, conflicting_reqs):
+            # type: (str, Set[Tuple[str, str]]) -> None
+            format_string = (
+                "Some build dependencies for {requirement} "
+                "conflict with {conflicting_with}: {description}."
+            )
+            error_message = format_string.format(
+                requirement=self.req,
+                conflicting_with=conflicting_with,
+                description=', '.join(
+                    '{} is incompatible with {}'.format(installed, wanted)
+                    for installed, wanted in sorted(conflicting)
+                )
+            )
+            raise InstallationError(error_message)
+
+        # Isolate in a BuildEnvironment and install the build-time
+        # requirements.
+        pyproject_requires = self.req.pyproject_requires
+        assert pyproject_requires is not None
+
+        self.req.build_env = BuildEnvironment()
+        self.req.build_env.install_requirements(
+            finder, pyproject_requires, 'overlay',
+            "Installing build dependencies"
+        )
+        conflicting, missing = self.req.build_env.check_requirements(
+            self.req.requirements_to_check
+        )
+        if conflicting:
+            _raise_conflicts("PEP 517/518 supported requirements",
+                             conflicting)
+        if missing:
+            logger.warning(
+                "Missing build requirements in pyproject.toml for %s.",
+                self.req,
+            )
+            logger.warning(
+                "The project does not specify a build backend, and "
+                "pip cannot fall back to setuptools without %s.",
+                " and ".join(map(repr, sorted(missing)))
+            )
+        # Install any extra build dependencies that the backend requests.
+        # This must be done in a second pass, as the pyproject.toml
+        # dependencies must be installed before we can call the backend.
+        with self.req.build_env:
+            runner = runner_with_spinner_message(
+                "Getting requirements to build wheel"
+            )
+            backend = self.req.pep517_backend
+            assert backend is not None
+            with backend.subprocess_runner(runner):
+                reqs = backend.get_requires_for_build_wheel()
+
+        conflicting, missing = self.req.build_env.check_requirements(reqs)
+        if conflicting:
+            _raise_conflicts("the backend dependencies", conflicting)
+        self.req.build_env.install_requirements(
+            finder, missing, 'normal',
+            "Installing backend dependencies"
+        )