editable_wheel.py

"""
Create a wheel that, when installed, will make the source package 'editable'
(add it to the interpreter's path, including metadata) per PEP 660. Replaces
'setup.py develop'.

.. note::
   One of the mechanisms briefly mentioned in PEP 660 to implement editable installs is
   to create a separated directory inside ``build`` and use a .pth file to point to that
   directory. In the context of this file such directory is referred as
   *auxiliary build directory* or ``auxiliary_dir``.
"""

import logging
import io
import os
import shutil
import traceback
from contextlib import suppress
from enum import Enum
from inspect import cleandoc
from itertools import chain, starmap
from pathlib import Path
from tempfile import TemporaryDirectory
from typing import (
    TYPE_CHECKING,
    Dict,
    Iterable,
    Iterator,
    List,
    Mapping,
    Optional,
    Protocol,
    Tuple,
    TypeVar,
    cast,
)

from .. import (
    Command,
    _normalization,
    _path,
    errors,
    namespaces,
)
from .._path import StrPath
from ..compat import py39
from ..discovery import find_package_path
from ..dist import Distribution
from ..warnings import (
    InformationOnly,
    SetuptoolsDeprecationWarning,
    SetuptoolsWarning,
)
from .build import build as build_cls
from .build_py import build_py as build_py_cls
from .dist_info import dist_info as dist_info_cls
from .egg_info import egg_info as egg_info_cls
from .install import install as install_cls
from .install_scripts import install_scripts as install_scripts_cls

if TYPE_CHECKING:
    from wheel.wheelfile import WheelFile  # type:ignore[import-untyped] # noqa

_P = TypeVar("_P", bound=StrPath)
_logger = logging.getLogger(__name__)


class _EditableMode(Enum):
    """
    Possible editable installation modes:
    `lenient` (new files automatically added to the package - DEFAULT);
    `strict` (requires a new installation when files are added/removed); or
    `compat` (attempts to emulate `python setup.py develop` - DEPRECATED).
    """

    STRICT = "strict"
    LENIENT = "lenient"
    COMPAT = "compat"  # TODO: Remove `compat` after Dec/2022.

    @classmethod
    def convert(cls, mode: Optional[str]) -> "_EditableMode":
        if not mode:
            return _EditableMode.LENIENT  # default

        _mode = mode.upper()
        if _mode not in _EditableMode.__members__:
            raise errors.OptionError(f"Invalid editable mode: {mode!r}. Try: 'strict'.")

        if _mode == "COMPAT":
            SetuptoolsDeprecationWarning.emit(
                "Compat editable installs",
                """
                The 'compat' editable mode is transitional and will be removed
                in future versions of `setuptools`.
                Please adapt your code accordingly to use either the 'strict' or the
                'lenient' modes.
                """,
                see_docs="userguide/development_mode.html",
                # TODO: define due_date
                # There is a series of shortcomings with the available editable install
                # methods, and they are very controversial. This is something that still
                # needs work.
                # Moreover, `pip` is still hiding this warning, so users are not aware.
            )

        return _EditableMode[_mode]


_STRICT_WARNING = """
New or renamed files may not be automatically picked up without a new installation.
"""

_LENIENT_WARNING = """
Options like `package-data`, `include/exclude-package-data` or
`packages.find.exclude/include` may have no effect.
"""


class editable_wheel(Command):
    """Build 'editable' wheel for development.
    This command is private and reserved for internal use of setuptools,
    users should rely on ``setuptools.build_meta`` APIs.
    """

    description = "DO NOT CALL DIRECTLY, INTERNAL ONLY: create PEP 660 editable wheel"

    user_options = [
        ("dist-dir=", "d", "directory to put final built distributions in"),
        ("dist-info-dir=", "I", "path to a pre-build .dist-info directory"),
        ("mode=", None, cleandoc(_EditableMode.__doc__ or "")),
    ]

    def initialize_options(self):
        self.dist_dir = None
        self.dist_info_dir = None
        self.project_dir = None
        self.mode = None

    def finalize_options(self):
        dist = self.distribution
        self.project_dir = dist.src_root or os.curdir
        self.package_dir = dist.package_dir or {}
        self.dist_dir = Path(self.dist_dir or os.path.join(self.project_dir, "dist"))

    def run(self):
        try:
            self.dist_dir.mkdir(exist_ok=True)
            self._ensure_dist_info()

            # Add missing dist_info files
            self.reinitialize_command("bdist_wheel")
            bdist_wheel = self.get_finalized_command("bdist_wheel")
            bdist_wheel.write_wheelfile(self.dist_info_dir)

            self._create_wheel_file(bdist_wheel)
        except Exception:
            traceback.print_exc()
            project = self.distribution.name or self.distribution.get_name()
            _DebuggingTips.emit(project=project)
            raise

    def _ensure_dist_info(self):
        if self.dist_info_dir is None:
            dist_info = cast(dist_info_cls, self.reinitialize_command("dist_info"))
            dist_info.output_dir = self.dist_dir
            dist_info.ensure_finalized()
            dist_info.run()
            self.dist_info_dir = dist_info.dist_info_dir
        else:
            assert str(self.dist_info_dir).endswith(".dist-info")
            assert Path(self.dist_info_dir, "METADATA").exists()

    def _install_namespaces(self, installation_dir, pth_prefix):
        # XXX: Only required to support the deprecated namespace practice
        dist = self.distribution
        if not dist.namespace_packages:
            return

        src_root = Path(self.project_dir, self.package_dir.get("", ".")).resolve()
        installer = _NamespaceInstaller(dist, installation_dir, pth_prefix, src_root)
        installer.install_namespaces()

    def _find_egg_info_dir(self) -> Optional[str]:
        parent_dir = Path(self.dist_info_dir).parent if self.dist_info_dir else Path()
        candidates = map(str, parent_dir.glob("*.egg-info"))
        return next(candidates, None)

    def _configure_build(
        self, name: str, unpacked_wheel: StrPath, build_lib: StrPath, tmp_dir: StrPath
    ):
        """Configure commands to behave in the following ways:

        - Build commands can write to ``build_lib`` if they really want to...
          (but this folder is expected to be ignored and modules are expected to live
          in the project directory...)
        - Binary extensions should be built in-place (editable_mode = True)
        - Data/header/script files are not part of the "editable" specification
          so they are written directly to the unpacked_wheel directory.
        """
        # Non-editable files (data, headers, scripts) are written directly to the
        # unpacked_wheel

        dist = self.distribution
        wheel = str(unpacked_wheel)
        build_lib = str(build_lib)
        data = str(Path(unpacked_wheel, f"{name}.data", "data"))
        headers = str(Path(unpacked_wheel, f"{name}.data", "headers"))
        scripts = str(Path(unpacked_wheel, f"{name}.data", "scripts"))

        # egg-info may be generated again to create a manifest (used for package data)
        egg_info = cast(
            egg_info_cls, dist.reinitialize_command("egg_info", reinit_subcommands=True)
        )
        egg_info.egg_base = str(tmp_dir)
        egg_info.ignore_egg_info_in_manifest = True

        build = cast(
            build_cls, dist.reinitialize_command("build", reinit_subcommands=True)
        )
        install = cast(
            install_cls, dist.reinitialize_command("install", reinit_subcommands=True)
        )

        build.build_platlib = build.build_purelib = build.build_lib = build_lib
        install.install_purelib = install.install_platlib = install.install_lib = wheel
        install.install_scripts = build.build_scripts = scripts
        install.install_headers = headers
        install.install_data = data

        install_scripts = cast(
            install_scripts_cls, dist.get_command_obj("install_scripts")
        )
        install_scripts.no_ep = True

        build.build_temp = str(tmp_dir)

        build_py = cast(build_py_cls, dist.get_command_obj("build_py"))
        build_py.compile = False
        build_py.existing_egg_info_dir = self._find_egg_info_dir()

        self._set_editable_mode()

        build.ensure_finalized()
        install.ensure_finalized()

    def _set_editable_mode(self):
        """Set the ``editable_mode`` flag in the build sub-commands"""
        dist = self.distribution
        build = dist.get_command_obj("build")
        # TODO: Update typeshed distutils stubs to overload non-None return type by default
        for cmd_name in build.get_sub_commands():
            cmd = dist.get_command_obj(cmd_name)
            if hasattr(cmd, "editable_mode"):
                cmd.editable_mode = True
            elif hasattr(cmd, "inplace"):
                cmd.inplace = True  # backward compatibility with distutils

    def _collect_build_outputs(self) -> Tuple[List[str], Dict[str, str]]:
        files: List[str] = []
        mapping: Dict[str, str] = {}
        build = self.get_finalized_command("build")

        for cmd_name in build.get_sub_commands():
            cmd = self.get_finalized_command(cmd_name)
            if hasattr(cmd, "get_outputs"):
                files.extend(cmd.get_outputs() or [])
            if hasattr(cmd, "get_output_mapping"):
                mapping.update(cmd.get_output_mapping() or {})

        return files, mapping

    def _run_build_commands(
        self,
        dist_name: str,
        unpacked_wheel: StrPath,
        build_lib: StrPath,
        tmp_dir: StrPath,
    ) -> Tuple[List[str], Dict[str, str]]:
        self._configure_build(dist_name, unpacked_wheel, build_lib, tmp_dir)
        self._run_build_subcommands()
        files, mapping = self._collect_build_outputs()
        self._run_install("headers")
        self._run_install("scripts")
        self._run_install("data")
        return files, mapping

    def _run_build_subcommands(self) -> None:
        """
        Issue #3501 indicates that some plugins/customizations might rely on:

        1. ``build_py`` not running
        2. ``build_py`` always copying files to ``build_lib``

        However both these assumptions may be false in editable_wheel.
        This method implements a temporary workaround to support the ecosystem
        while the implementations catch up.
        """
        # TODO: Once plugins/customisations had the chance to catch up, replace
        #       `self._run_build_subcommands()` with `self.run_command("build")`.
        #       Also remove _safely_run, TestCustomBuildPy. Suggested date: Aug/2023.
        build = self.get_finalized_command("build")
        for name in build.get_sub_commands():
            cmd = self.get_finalized_command(name)
            if name == "build_py" and type(cmd) != build_py_cls:
                self._safely_run(name)
            else:
                self.run_command(name)

    def _safely_run(self, cmd_name: str):
        try:
            return self.run_command(cmd_name)
        except Exception:
            SetuptoolsDeprecationWarning.emit(
                "Customization incompatible with editable install",
                f"""
                {traceback.format_exc()}

                If you are seeing this warning it is very likely that a setuptools
                plugin or customization overrides the `{cmd_name}` command, without
                taking into consideration how editable installs run build steps
                starting from setuptools v64.0.0.

                Plugin authors and developers relying on custom build steps are
                encouraged to update their `{cmd_name}` implementation considering the
                information about editable installs in
                https://setuptools.pypa.io/en/latest/userguide/extension.html.

                For the time being `setuptools` will silence this error and ignore
                the faulty command, but this behaviour will change in future versions.
                """,
                # TODO: define due_date
                # There is a series of shortcomings with the available editable install
                # methods, and they are very controversial. This is something that still
                # needs work.
            )

    def _create_wheel_file(self, bdist_wheel):
        from wheel.wheelfile import WheelFile

        dist_info = self.get_finalized_command("dist_info")
        dist_name = dist_info.name
        tag = "-".join(bdist_wheel.get_tag())
        build_tag = "0.editable"  # According to PEP 427 needs to start with digit
        archive_name = f"{dist_name}-{build_tag}-{tag}.whl"
        wheel_path = Path(self.dist_dir, archive_name)
        if wheel_path.exists():
            wheel_path.unlink()

        unpacked_wheel = TemporaryDirectory(suffix=archive_name)
        build_lib = TemporaryDirectory(suffix=".build-lib")
        build_tmp = TemporaryDirectory(suffix=".build-temp")

        with unpacked_wheel as unpacked, build_lib as lib, build_tmp as tmp:
            unpacked_dist_info = Path(unpacked, Path(self.dist_info_dir).name)
            shutil.copytree(self.dist_info_dir, unpacked_dist_info)
            self._install_namespaces(unpacked, dist_name)
            files, mapping = self._run_build_commands(dist_name, unpacked, lib, tmp)
            strategy = self._select_strategy(dist_name, tag, lib)
            with strategy, WheelFile(wheel_path, "w") as wheel_obj:
                strategy(wheel_obj, files, mapping)
                wheel_obj.write_files(unpacked)

        return wheel_path

    def _run_install(self, category: str):
        has_category = getattr(self.distribution, f"has_{category}", None)
        if has_category and has_category():
            _logger.info(f"Installing {category} as non editable")
            self.run_command(f"install_{category}")

    def _select_strategy(
        self,
        name: str,
        tag: str,
        build_lib: StrPath,
    ) -> "EditableStrategy":
        """Decides which strategy to use to implement an editable installation."""
        build_name = f"__editable__.{name}-{tag}"
        project_dir = Path(self.project_dir)
        mode = _EditableMode.convert(self.mode)

        if mode is _EditableMode.STRICT:
            auxiliary_dir = _empty_dir(Path(self.project_dir, "build", build_name))
            return _LinkTree(self.distribution, name, auxiliary_dir, build_lib)

        packages = _find_packages(self.distribution)
        has_simple_layout = _simple_layout(packages, self.package_dir, project_dir)
        is_compat_mode = mode is _EditableMode.COMPAT
        if set(self.package_dir) == {""} and has_simple_layout or is_compat_mode:
            # src-layout(ish) is relatively safe for a simple pth file
            src_dir = self.package_dir.get("", ".")
            return _StaticPth(self.distribution, name, [Path(project_dir, src_dir)])

        # Use a MetaPathFinder to avoid adding accidental top-level packages/modules
        return _TopLevelFinder(self.distribution, name)


class EditableStrategy(Protocol):
    def __call__(
        self, wheel: "WheelFile", files: List[str], mapping: Dict[str, str]
    ): ...

    def __enter__(self): ...

    def __exit__(self, _exc_type, _exc_value, _traceback): ...


class _StaticPth:
    def __init__(self, dist: Distribution, name: str, path_entries: List[Path]):
        self.dist = dist
        self.name = name
        self.path_entries = path_entries

    def __call__(self, wheel: "WheelFile", files: List[str], mapping: Dict[str, str]):
        entries = "\n".join(str(p.resolve()) for p in self.path_entries)
        contents = _encode_pth(f"{entries}\n")
        wheel.writestr(f"__editable__.{self.name}.pth", contents)

    def __enter__(self):
        msg = f"""
        Editable install will be performed using .pth file to extend `sys.path` with:
        {list(map(os.fspath, self.path_entries))!r}
        """
        _logger.warning(msg + _LENIENT_WARNING)
        return self

    def __exit__(self, _exc_type, _exc_value, _traceback): ...


class _LinkTree(_StaticPth):
    """
    Creates a ``.pth`` file that points to a link tree in the ``auxiliary_dir``.

    This strategy will only link files (not dirs), so it can be implemented in
    any OS, even if that means using hardlinks instead of symlinks.

    By collocating ``auxiliary_dir`` and the original source code, limitations
    with hardlinks should be avoided.
    """

    def __init__(
        self,
        dist: Distribution,
        name: str,
        auxiliary_dir: StrPath,
        build_lib: StrPath,
    ):
        self.auxiliary_dir = Path(auxiliary_dir)
        self.build_lib = Path(build_lib).resolve()
        # TODO: Update typeshed distutils stubs to overload non-None return type by default
        self._file = dist.get_command_obj("build_py").copy_file  # type: ignore[union-attr]
        super().__init__(dist, name, [self.auxiliary_dir])

    def __call__(self, wheel: "WheelFile", files: List[str], mapping: Dict[str, str]):
        self._create_links(files, mapping)
        super().__call__(wheel, files, mapping)

    def _normalize_output(self, file: str) -> Optional[str]:
        # Files relative to build_lib will be normalized to None
        with suppress(ValueError):
            path = Path(file).resolve().relative_to(self.build_lib)
            return str(path).replace(os.sep, '/')
        return None

    def _create_file(self, relative_output: str, src_file: str, link=None):
        dest = self.auxiliary_dir / relative_output
        if not dest.parent.is_dir():
            dest.parent.mkdir(parents=True)
        # TODO: Update typeshed distutils stubs so distutils.cmd.Command.copy_file, accepts PathLike
        # same with methods used by copy_file
        self._file(src_file, dest, link=link)  # type: ignore[arg-type]

    def _create_links(self, outputs, output_mapping):
        self.auxiliary_dir.mkdir(parents=True, exist_ok=True)
        link_type = "sym" if _can_symlink_files(self.auxiliary_dir) else "hard"
        mappings = {self._normalize_output(k): v for k, v in output_mapping.items()}
        mappings.pop(None, None)  # remove files that are not relative to build_lib

        for output in outputs:
            relative = self._normalize_output(output)
            if relative and relative not in mappings:
                self._create_file(relative, output)

        for relative, src in mappings.items():
            self._create_file(relative, src, link=link_type)

    def __enter__(self):
        msg = "Strict editable install will be performed using a link tree.\n"
        _logger.warning(msg + _STRICT_WARNING)
        return self

    def __exit__(self, _exc_type, _exc_value, _traceback):
        msg = f"""\n
        Strict editable installation performed using the auxiliary directory:
            {self.auxiliary_dir}

        Please be careful to not remove this directory, otherwise you might not be able
        to import/use your package.
        """
        InformationOnly.emit("Editable installation.", msg)


class _TopLevelFinder:
    def __init__(self, dist: Distribution, name: str):
        self.dist = dist
        self.name = name

    def __call__(self, wheel: "WheelFile", files: List[str], mapping: Dict[str, str]):
        src_root = self.dist.src_root or os.curdir
        top_level = chain(_find_packages(self.dist), _find_top_level_modules(self.dist))
        package_dir = self.dist.package_dir or {}
        roots = _find_package_roots(top_level, package_dir, src_root)

        namespaces_: Dict[str, List[str]] = dict(
            chain(
                _find_namespaces(self.dist.packages or [], roots),
                ((ns, []) for ns in _find_virtual_namespaces(roots)),
            )
        )

        legacy_namespaces = {
            pkg: find_package_path(pkg, roots, self.dist.src_root or "")
            for pkg in self.dist.namespace_packages or []
        }

        mapping = {**roots, **legacy_namespaces}
        # ^-- We need to explicitly add the legacy_namespaces to the mapping to be
        #     able to import their modules even if another package sharing the same
        #     namespace is installed in a conventional (non-editable) way.

        name = f"__editable__.{self.name}.finder"
        finder = _normalization.safe_identifier(name)
        content = bytes(_finder_template(name, mapping, namespaces_), "utf-8")
        wheel.writestr(f"{finder}.py", content)

        content = _encode_pth(f"import {finder}; {finder}.install()")
        wheel.writestr(f"__editable__.{self.name}.pth", content)

    def __enter__(self):
        msg = "Editable install will be performed using a meta path finder.\n"
        _logger.warning(msg + _LENIENT_WARNING)
        return self

    def __exit__(self, _exc_type, _exc_value, _traceback):
        msg = """\n
        Please be careful with folders in your working directory with the same
        name as your package as they may take precedence during imports.
        """
        InformationOnly.emit("Editable installation.", msg)


def _encode_pth(content: str) -> bytes:
    """.pth files are always read with 'locale' encoding, the recommendation
    from the cpython core developers is to write them as ``open(path, "w")``
    and ignore warnings (see python/cpython#77102, pypa/setuptools#3937).
    This function tries to simulate this behaviour without having to create an
    actual file, in a way that supports a range of active Python versions.
    (There seems to be some variety in the way different version of Python handle
    ``encoding=None``, not all of them use ``locale.getpreferredencoding(False)``).
    """
    with io.BytesIO() as buffer:
        wrapper = io.TextIOWrapper(buffer, encoding=py39.LOCALE_ENCODING)
        wrapper.write(content)
        wrapper.flush()
        buffer.seek(0)
        return buffer.read()


def _can_symlink_files(base_dir: Path) -> bool:
    with TemporaryDirectory(dir=str(base_dir.resolve())) as tmp:
        path1, path2 = Path(tmp, "file1.txt"), Path(tmp, "file2.txt")
        path1.write_text("file1", encoding="utf-8")
        with suppress(AttributeError, NotImplementedError, OSError):
            os.symlink(path1, path2)
            if path2.is_symlink() and path2.read_text(encoding="utf-8") == "file1":
                return True

        try:
            os.link(path1, path2)  # Ensure hard links can be created
        except Exception as ex:
            msg = (
                "File system does not seem to support either symlinks or hard links. "
                "Strict editable installs require one of them to be supported."
            )
            raise LinksNotSupported(msg) from ex
        return False


def _simple_layout(
    packages: Iterable[str], package_dir: Dict[str, str], project_dir: StrPath
) -> bool:
    """Return ``True`` if:
    - all packages are contained by the same parent directory, **and**
    - all packages become importable if the parent directory is added to ``sys.path``.

    >>> _simple_layout(['a'], {"": "src"}, "/tmp/myproj")
    True
    >>> _simple_layout(['a', 'a.b'], {"": "src"}, "/tmp/myproj")
    True
    >>> _simple_layout(['a', 'a.b'], {}, "/tmp/myproj")
    True
    >>> _simple_layout(['a', 'a.a1', 'a.a1.a2', 'b'], {"": "src"}, "/tmp/myproj")
    True
    >>> _simple_layout(['a', 'a.a1', 'a.a1.a2', 'b'], {"a": "a", "b": "b"}, ".")
    True
    >>> _simple_layout(['a', 'a.a1', 'a.a1.a2', 'b'], {"a": "_a", "b": "_b"}, ".")
    False
    >>> _simple_layout(['a', 'a.a1', 'a.a1.a2', 'b'], {"a": "_a"}, "/tmp/myproj")
    False
    >>> _simple_layout(['a', 'a.a1', 'a.a1.a2', 'b'], {"a.a1.a2": "_a2"}, ".")
    False
    >>> _simple_layout(['a', 'a.b'], {"": "src", "a.b": "_ab"}, "/tmp/myproj")
    False
    >>> # Special cases, no packages yet:
    >>> _simple_layout([], {"": "src"}, "/tmp/myproj")
    True
    >>> _simple_layout([], {"a": "_a", "": "src"}, "/tmp/myproj")
    False
    """
    layout = {pkg: find_package_path(pkg, package_dir, project_dir) for pkg in packages}
    if not layout:
        return set(package_dir) in ({}, {""})
    parent = os.path.commonpath(starmap(_parent_path, layout.items()))
    return all(
        _path.same_path(Path(parent, *key.split('.')), value)
        for key, value in layout.items()
    )


def _parent_path(pkg, pkg_path):
    """Infer the parent path containing a package, that if added to ``sys.path`` would
    allow importing that package.
    When ``pkg`` is directly mapped into a directory with a different name, return its
    own path.
    >>> _parent_path("a", "src/a")
    'src'
    >>> _parent_path("b", "src/c")
    'src/c'
    """
    parent = pkg_path[: -len(pkg)] if pkg_path.endswith(pkg) else pkg_path
    return parent.rstrip("/" + os.sep)


def _find_packages(dist: Distribution) -> Iterator[str]:
    yield from iter(dist.packages or [])

    py_modules = dist.py_modules or []
    nested_modules = [mod for mod in py_modules if "." in mod]
    if dist.ext_package:
        yield dist.ext_package
    else:
        ext_modules = dist.ext_modules or []
        nested_modules += [x.name for x in ext_modules if "." in x.name]

    for module in nested_modules:
        package, _, _ = module.rpartition(".")
        yield package


def _find_top_level_modules(dist: Distribution) -> Iterator[str]:
    py_modules = dist.py_modules or []
    yield from (mod for mod in py_modules if "." not in mod)

    if not dist.ext_package:
        ext_modules = dist.ext_modules or []
        yield from (x.name for x in ext_modules if "." not in x.name)


def _find_package_roots(
    packages: Iterable[str],
    package_dir: Mapping[str, str],
    src_root: StrPath,
) -> Dict[str, str]:
    pkg_roots: Dict[str, str] = {
        pkg: _absolute_root(find_package_path(pkg, package_dir, src_root))
        for pkg in sorted(packages)
    }

    return _remove_nested(pkg_roots)


def _absolute_root(path: StrPath) -> str:
    """Works for packages and top-level modules"""
    path_ = Path(path)
    parent = path_.parent

    if path_.exists():
        return str(path_.resolve())
    else:
        return str(parent.resolve() / path_.name)


def _find_virtual_namespaces(pkg_roots: Dict[str, str]) -> Iterator[str]:
    """By carefully designing ``package_dir``, it is possible to implement the logical
    structure of PEP 420 in a package without the corresponding directories.

    Moreover a parent package can be purposefully/accidentally skipped in the discovery
    phase (e.g. ``find_packages(include=["mypkg.*"])``, when ``mypkg.foo`` is included
    by ``mypkg`` itself is not).
    We consider this case to also be a virtual namespace (ignoring the original
    directory) to emulate a non-editable installation.

    This function will try to find these kinds of namespaces.
    """
    for pkg in pkg_roots:
        if "." not in pkg:
            continue
        parts = pkg.split(".")
        for i in range(len(parts) - 1, 0, -1):
            partial_name = ".".join(parts[:i])
            path = Path(find_package_path(partial_name, pkg_roots, ""))
            if not path.exists() or partial_name not in pkg_roots:
                # partial_name not in pkg_roots ==> purposefully/accidentally skipped
                yield partial_name


def _find_namespaces(
    packages: List[str], pkg_roots: Dict[str, str]
) -> Iterator[Tuple[str, List[str]]]:
    for pkg in packages:
        path = find_package_path(pkg, pkg_roots, "")
        if Path(path).exists() and not Path(path, "__init__.py").exists():
            yield (pkg, [path])


def _remove_nested(pkg_roots: Dict[str, str]) -> Dict[str, str]:
    output = dict(pkg_roots.copy())

    for pkg, path in reversed(list(pkg_roots.items())):
        if any(
            pkg != other and _is_nested(pkg, path, other, other_path)
            for other, other_path in pkg_roots.items()
        ):
            output.pop(pkg)

    return output


def _is_nested(pkg: str, pkg_path: str, parent: str, parent_path: str) -> bool:
    """
    Return ``True`` if ``pkg`` is nested inside ``parent`` both logically and in the
    file system.
    >>> _is_nested("a.b", "path/a/b", "a", "path/a")
    True
    >>> _is_nested("a.b", "path/a/b", "a", "otherpath/a")
    False
    >>> _is_nested("a.b", "path/a/b", "c", "path/c")
    False
    >>> _is_nested("a.a", "path/a/a", "a", "path/a")
    True
    >>> _is_nested("b.a", "path/b/a", "a", "path/a")
    False
    """
    norm_pkg_path = _path.normpath(pkg_path)
    rest = pkg.replace(parent, "", 1).strip(".").split(".")
    return pkg.startswith(parent) and norm_pkg_path == _path.normpath(
        Path(parent_path, *rest)
    )


def _empty_dir(dir_: _P) -> _P:
    """Create a directory ensured to be empty. Existing files may be removed."""
    shutil.rmtree(dir_, ignore_errors=True)
    os.makedirs(dir_)
    return dir_


class _NamespaceInstaller(namespaces.Installer):
    def __init__(self, distribution, installation_dir, editable_name, src_root):
        self.distribution = distribution
        self.src_root = src_root
        self.installation_dir = installation_dir
        self.editable_name = editable_name
        self.outputs = []
        self.dry_run = False

    def _get_nspkg_file(self):
        """Installation target."""
        return os.path.join(self.installation_dir, self.editable_name + self.nspkg_ext)

    def _get_root(self):
        """Where the modules/packages should be loaded from."""
        return repr(str(self.src_root))


_FINDER_TEMPLATE = """\
import sys
from importlib.machinery import ModuleSpec, PathFinder
from importlib.machinery import all_suffixes as module_suffixes
from importlib.util import spec_from_file_location
from itertools import chain
from pathlib import Path

MAPPING = {mapping!r}
NAMESPACES = {namespaces!r}
PATH_PLACEHOLDER = {name!r} + ".__path_hook__"


class _EditableFinder:  # MetaPathFinder
    @classmethod
    def find_spec(cls, fullname, path=None, target=None):
        extra_path = []

        # Top-level packages and modules (we know these exist in the FS)
        if fullname in MAPPING:
            pkg_path = MAPPING[fullname]
            return cls._find_spec(fullname, Path(pkg_path))

        # Handle immediate children modules (required for namespaces to work)
        # To avoid problems with case sensitivity in the file system we delegate
        # to the importlib.machinery implementation.
        parent, _, child = fullname.rpartition(".")
        if parent and parent in MAPPING:
            return PathFinder.find_spec(fullname, path=[MAPPING[parent], *extra_path])

        # Other levels of nesting should be handled automatically by importlib
        # using the parent path.
        return None

    @classmethod
    def _find_spec(cls, fullname, candidate_path):
        init = candidate_path / "__init__.py"
        candidates = (candidate_path.with_suffix(x) for x in module_suffixes())
        for candidate in chain([init], candidates):
            if candidate.exists():
                return spec_from_file_location(fullname, candidate)


class _EditableNamespaceFinder:  # PathEntryFinder
    @classmethod
    def _path_hook(cls, path):
        if path == PATH_PLACEHOLDER:
            return cls
        raise ImportError

    @classmethod
    def _paths(cls, fullname):
        # Ensure __path__ is not empty for the spec to be considered a namespace.
        return NAMESPACES[fullname] or MAPPING.get(fullname) or [PATH_PLACEHOLDER]

    @classmethod
    def find_spec(cls, fullname, target=None):
        if fullname in NAMESPACES:
            spec = ModuleSpec(fullname, None, is_package=True)
            spec.submodule_search_locations = cls._paths(fullname)
            return spec
        return None

    @classmethod
    def find_module(cls, fullname):
        return None


def install():
    if not any(finder == _EditableFinder for finder in sys.meta_path):
        sys.meta_path.append(_EditableFinder)

    if not NAMESPACES:
        return

    if not any(hook == _EditableNamespaceFinder._path_hook for hook in sys.path_hooks):
        # PathEntryFinder is needed to create NamespaceSpec without private APIS
        sys.path_hooks.append(_EditableNamespaceFinder._path_hook)
    if PATH_PLACEHOLDER not in sys.path:
        sys.path.append(PATH_PLACEHOLDER)  # Used just to trigger the path hook
"""


def _finder_template(
    name: str, mapping: Mapping[str, str], namespaces: Dict[str, List[str]]
) -> str:
    """Create a string containing the code for the``MetaPathFinder`` and
    ``PathEntryFinder``.
    """
    mapping = dict(sorted(mapping.items(), key=lambda p: p[0]))
    return _FINDER_TEMPLATE.format(name=name, mapping=mapping, namespaces=namespaces)


class LinksNotSupported(errors.FileError):
    """File system does not seem to support either symlinks or hard links."""


class _DebuggingTips(SetuptoolsWarning):
    _SUMMARY = "Problem in editable installation."
    _DETAILS = """
    An error happened while installing `{project}` in editable mode.

    The following steps are recommended to help debug this problem:

    - Try to install the project normally, without using the editable mode.
      Does the error still persist?
      (If it does, try fixing the problem before attempting the editable mode).
    - If you are using binary extensions, make sure you have all OS-level
      dependencies installed (e.g. compilers, toolchains, binary libraries, ...).
    - Try the latest version of setuptools (maybe the error was already fixed).
    - If you (or your project dependencies) are using any setuptools extension
      or customization, make sure they support the editable mode.

    After following the steps above, if the problem still persists and
    you think this is related to how setuptools handles editable installations,
    please submit a reproducible example
    (see https://stackoverflow.com/help/minimal-reproducible-example) to:

        https://github.com/pypa/setuptools/issues
    """
    _SEE_DOCS = "userguide/development_mode.html"