def prepare_linked_requirement(
        self,
        req,  # type: InstallRequirement
    ):
        # type: (...) -> AbstractDistribution
        """Prepare a requirement that would be obtained from req.link
        """
        assert req.link
        link = req.link

        # TODO: Breakup into smaller functions
        if link.scheme == 'file':
            path = link.file_path
            logger.info('Processing %s', display_path(path))
        else:
            logger.info('Collecting %s', req.req or req)

        download_dir = self.download_dir
        if link.is_wheel and self.wheel_download_dir:
            # when doing 'pip wheel` we download wheels to a
            # dedicated dir.
            download_dir = self.wheel_download_dir

        if link.is_wheel:
            if download_dir:
                # When downloading, we only unpack wheels to get
                # metadata.
                autodelete_unpacked = True
            else:
                # When installing a wheel, we use the unpacked
                # wheel.
                autodelete_unpacked = False
        else:
            # We always delete unpacked sdists after pip runs.
            autodelete_unpacked = True

        with indent_log():
            # Since source_dir is only set for editable requirements.
            assert req.source_dir is None
            if link.is_existing_dir():
                # Build local directories in place.
                req.source_dir = link.file_path
            else:
                req.ensure_has_source_dir(self.build_dir, autodelete_unpacked)
                # If a checkout exists, it's unwise to keep going.  version
                # inconsistencies are logged later, but do not fail the
                # installation.
                # FIXME: this won't upgrade when there's an existing
                # package unpacked in `req.source_dir`
                if os.path.exists(os.path.join(req.source_dir, 'setup.py')):
                    raise PreviousBuildDirError(
                        "pip can't proceed with requirements '{}' due to a"
                        " pre-existing build directory ({}). This is "
                        "likely due to a previous installation that failed"
                        ". pip is being responsible and not assuming it "
                        "can delete this. Please delete it and try again."
                        .format(req, req.source_dir)
                    )

            # Now that we have the real link, we can tell what kind of
            # requirements we have and raise some more informative errors
            # than otherwise. (For example, we can raise VcsHashUnsupported
            # for a VCS URL rather than HashMissing.)
            if self.require_hashes:
                # We could check these first 2 conditions inside
                # unpack_url and save repetition of conditions, but then
                # we would report less-useful error messages for
                # unhashable requirements, complaining that there's no
                # hash provided.
                if link.is_vcs:
                    raise VcsHashUnsupported()
                elif link.is_existing_dir():
                    raise DirectoryUrlHashUnsupported()
                if not req.original_link and not req.is_pinned:
                    # Unpinned packages are asking for trouble when a new
                    # version is uploaded. This isn't a security check, but
                    # it saves users a surprising hash mismatch in the
                    # future.
                    #
                    # file:/// URLs aren't pinnable, so don't complain
                    # about them not being pinned.
                    raise HashUnpinned()

            hashes = req.hashes(trust_internet=not self.require_hashes)
            if self.require_hashes and not hashes:
                # Known-good hashes are missing for this requirement, so
                # shim it with a facade object that will provoke hash
                # computation and then raise a HashMissing exception
                # showing the user what the hash should be.
                hashes = MissingHashes()

            try:
                local_file = unpack_url(
                    link, req.source_dir, self.downloader, download_dir,
                    hashes=hashes,
                )
            except requests.HTTPError as exc:
                logger.critical(
                    'Could not install requirement %s because of error %s',
                    req,
                    exc,
                )
                raise InstallationError(
                    'Could not install requirement {} because of HTTP '
                    'error {} for URL {}'.format(req, exc, link)
                )

            # For use in later processing, preserve the file path on the
            # requirement.
            if local_file:
                req.local_file_path = local_file.path

            abstract_dist = _get_prepared_distribution(
                req, self.req_tracker, self.finder, self.build_isolation,
            )

            if download_dir:
                if link.is_existing_dir():
                    logger.info('Link is a directory, ignoring download_dir')
                elif local_file:
                    download_location = os.path.join(
                        download_dir, link.filename
                    )
                    if not os.path.exists(download_location):
                        shutil.copy(local_file.path, download_location)
                        logger.info(
                            'Saved %s', display_path(download_location)
                        )

            if self._download_should_save:
                # Make a .zip of the source_dir we already created.
                if link.is_vcs:
                    req.archive(self.download_dir)
        return abstract_dist
Prepare a requirement that would be obtained from req.link
        
product/gradle-plugin/src/main/python/pip/_internal/operations/prepare.py