added v3

venv/lib/python3.11/site-packages/setuptools/command/editable_wheel.py

@@ -0,0 +1,844 @@
+"""
+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 os
+import re
+import shutil
+import sys
+import traceback
+import warnings
+from contextlib import suppress
+from enum import Enum
+from inspect import cleandoc
+from itertools import chain
+from pathlib import Path
+from tempfile import TemporaryDirectory
+from typing import (
+    TYPE_CHECKING,
+    Dict,
+    Iterable,
+    Iterator,
+    List,
+    Mapping,
+    Optional,
+    Tuple,
+    TypeVar,
+    Union,
+)
+
+from setuptools import Command, SetuptoolsDeprecationWarning, errors, namespaces
+from setuptools.command.build_py import build_py as build_py_cls
+from setuptools.discovery import find_package_path
+from setuptools.dist import Distribution
+
+if TYPE_CHECKING:
+    from wheel.wheelfile import WheelFile  # noqa
+
+if sys.version_info >= (3, 8):
+    from typing import Protocol
+elif TYPE_CHECKING:
+    from typing_extensions import Protocol
+else:
+    from abc import ABC as Protocol
+
+_Path = Union[str, Path]
+_P = TypeVar("_P", bound=_Path)
+_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":
+            msg = """
+            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.
+
+            For more information, please check:
+            https://setuptools.pypa.io/en/latest/userguide/development_mode.html
+            """
+            warnings.warn(msg, SetuptoolsDeprecationWarning)
+
+        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 reserved for internal use of setuptools).
+    """
+
+    description = "create a 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 as ex:
+            traceback.print_exc()
+            msg = """
+            Support for editable installs via PEP 660 was recently introduced
+            in `setuptools`. If you are seeing this error, please report to:
+
+            https://github.com/pypa/setuptools/issues
+
+            Meanwhile you can try the legacy behavior by setting an
+            environment variable and trying to install again:
+
+            SETUPTOOLS_ENABLE_FEATURES="legacy-editable"
+            """
+            raise errors.InternalError(cleandoc(msg)) from ex
+
+    def _ensure_dist_info(self):
+        if self.dist_info_dir is None:
+            dist_info = 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: _Path, build_lib: _Path, tmp_dir: _Path
+    ):
+        """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 = dist.reinitialize_command("egg_info", reinit_subcommands=True)
+        egg_info.egg_base = str(tmp_dir)
+        egg_info.ignore_egg_info_in_manifest = True
+
+        build = dist.reinitialize_command("build", reinit_subcommands=True)
+        install = 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 = dist.get_command_obj("install_scripts")
+        install_scripts.no_ep = True
+
+        build.build_temp = str(tmp_dir)
+
+        build_py = 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")
+        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: _Path, build_lib: _Path, tmp_dir: _Path
+    ) -> 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):
+        """
+        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: Command = 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:
+            msg = f"""{traceback.format_exc()}\n
+            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 v64.0.0.
+
+            Plugin authors and developers relying on custom build steps are encouraged
+            to update their `{cmd_name}` implementation considering the information in
+            https://setuptools.pypa.io/en/latest/userguide/extension.html
+            about editable installs.
+
+            For the time being `setuptools` will silence this error and ignore
+            the faulty command, but this behaviour will change in future versions.\n
+            """
+            warnings.warn(msg, SetuptoolsDeprecationWarning, stacklevel=2)
+
+    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_info.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: _Path,
+    ) -> "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 = bytes(f"{entries}\n", "utf-8")
+        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: _Path,
+        build_lib: _Path,
+    ):
+        self.auxiliary_dir = Path(auxiliary_dir)
+        self.build_lib = Path(build_lib).resolve()
+        self._file = dist.get_command_obj("build_py").copy_file
+        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)
+        self._file(src_file, dest, link=link)
+
+    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.
+        """
+        warnings.warn(msg, InformationOnly)
+
+
+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)),
+        ))
+
+        name = f"__editable__.{self.name}.finder"
+        finder = _make_identifier(name)
+        content = bytes(_finder_template(name, roots, namespaces_), "utf-8")
+        wheel.writestr(f"{finder}.py", content)
+
+        content = bytes(f"import {finder}; {finder}.install()", "utf-8")
+        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.
+        """
+        warnings.warn(msg, InformationOnly)
+
+
+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: Path
+) -> 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([_parent_path(k, v) for k, v in layout.items()])
+    return all(
+        _normalize_path(Path(parent, *key.split('.'))) == _normalize_path(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: _Path,
+) -> 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: _Path) -> 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 = _normalize_path(pkg_path)
+    rest = pkg.replace(parent, "", 1).strip(".").split(".")
+    return (
+        pkg.startswith(parent)
+        and norm_pkg_path == _normalize_path(Path(parent_path, *rest))
+    )
+
+
+def _normalize_path(filename: _Path) -> str:
+    """Normalize a file/dir name for comparison purposes"""
+    # See pkg_resources.normalize_path
+    file = os.path.abspath(filename) if sys.platform == 'cygwin' else filename
+    return os.path.normcase(os.path.realpath(os.path.normpath(file)))
+
+
+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_
+
+
+def _make_identifier(name: str) -> str:
+    """Make a string safe to be used as Python identifier.
+    >>> _make_identifier("12abc")
+    '_12abc'
+    >>> _make_identifier("__editable__.myns.pkg-78.9.3_local")
+    '__editable___myns_pkg_78_9_3_local'
+    """
+    safe = re.sub(r'\W|^(?=\d)', '_', name)
+    assert safe.isidentifier()
+    return safe
+
+
+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_target(self):
+        """Installation target."""
+        return os.path.join(self.installation_dir, self.editable_name)
+
+    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
+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):
+        for pkg, pkg_path in reversed(list(MAPPING.items())):
+            if fullname == pkg or fullname.startswith(f"{{pkg}}."):
+                rest = fullname.replace(pkg, "", 1).strip(".").split(".")
+                return cls._find_spec(fullname, Path(pkg_path, *rest))
+
+        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 InformationOnly(UserWarning):
+    """Currently there is no clear way of displaying messages to the users
+    that use the setuptools backend directly via ``pip``.
+    The only thing that might work is a warning, although it is not the
+    most appropriate tool for the job...
+    """
+
+
+class LinksNotSupported(errors.FileError):
+    """File system does not seem to support either symlinks or hard links."""