Option to use original package directory to install from pip.

[fx-kirin]

What's the problem this feature will solve?
Currently, pip install . command cannnot handle the relative path from Cargo.toml which is used in setup-tools-rust. Because installing from pip requires to copy the whole package to temporary directory and it breaks relative path link.

Installing the package through python setup.py install works completely. But trying to work with poetry requires to use pip. So I need some way to cope with the problem.

This issue might be related to PyO3/maturin#330.

Describe the solution you'd like
Want an option to use the original directory to install a python package not to use a temporary directory.

Alternative Solutions
Maybe an option to set current path to install package. But current --root option does not work.

Additional context
I modified the function _prepare_linked_requirement in pip/_internal/operations/prepare.py and the install was completed.

    def _prepare_linked_requirement(self, req, parallel_builds):
        # type: (InstallRequirement, bool) -> Distribution
        assert req.link
        link = req.link

        self._ensure_link_req_src_dir(req, parallel_builds)
        hashes = self._get_linked_req_hashes(req)
        if link.url not in self._downloaded:
            try:
                if not link.is_existing_dir():
                    local_file = unpack_url(
                        link, req.source_dir, self._download,
                        self.download_dir, hashes,
                    )
                else:
                    req.source_dir = link.file_path
                    local_file = None
            except NetworkConnectionError as exc:
                raise InstallationError(
                    'Could not install requirement {} because of HTTP '
                    'error {} for URL {}'.format(req, exc, link)
                )
        else:
            file_path, content_type = self._downloaded[link.url]
            if hashes:
                hashes.check_against_path(file_path)
            local_file = File(file_path, content_type)

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

        dist = _get_prepared_distribution(
            req, self.req_tracker, self.finder, self.build_isolation,
        )
        return dist

[sbidoul]

This has been implemented and will be in pip 21.1. You can try the main branch with --use-feature=in-tree-build.

[uranusjr]

See #9091

[fx-kirin]

Thanks!

[chriamue]

This has been implemented and will be in pip 21.1. You can try the main branch with --use-feature=in-tree-build.

PIP 21.1 is out now. I tested it with

pip install . --use-feature=in-tree-build

and it works now.