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[EDIT] FILE: _impl.py

import json
import os
import sys
import tempfile
from contextlib import contextmanager
from os.path import abspath
from os.path import join as pjoin
from subprocess import STDOUT, check_call, check_output
from typing import TYPE_CHECKING, Any, Iterator, Mapping, Optional, Sequence

from ._in_process import _in_proc_script_path

if TYPE_CHECKING:
    from typing import Protocol

class SubprocessRunner(Protocol):
        """A protocol for the subprocess runner."""

def __call__(
            self,
            cmd: Sequence[str],
            cwd: Optional[str] = None,
            extra_environ: Optional[Mapping[str, str]] = None,
        ) -> None:
            ...

def write_json(obj: Mapping[str, Any], path: str, **kwargs) -> None:
    with open(path, "w", encoding="utf-8") as f:
        json.dump(obj, f, **kwargs)

def read_json(path: str) -> Mapping[str, Any]:
    with open(path, encoding="utf-8") as f:
        return json.load(f)

class BackendUnavailable(Exception):
    """Will be raised if the backend cannot be imported in the hook process."""

def __init__(
        self,
        traceback: str,
        message: Optional[str] = None,
        backend_name: Optional[str] = None,
        backend_path: Optional[Sequence[str]] = None,
    ) -> None:
        # Preserving arg order for the sake of API backward compatibility.
        self.backend_name = backend_name
        self.backend_path = backend_path
        self.traceback = traceback
        super().__init__(message or "Error while importing backend")

class HookMissing(Exception):
    """Will be raised on missing hooks (if a fallback can't be used)."""

def __init__(self, hook_name: str) -> None:
        super().__init__(hook_name)
        self.hook_name = hook_name

class UnsupportedOperation(Exception):
    """May be raised by build_sdist if the backend indicates that it can't."""

def __init__(self, traceback: str) -> None:
        self.traceback = traceback

def default_subprocess_runner(
    cmd: Sequence[str],
    cwd: Optional[str] = None,
    extra_environ: Optional[Mapping[str, str]] = None,
) -> None:
    """The default method of calling the wrapper subprocess.

This uses :func:`subprocess.check_call` under the hood.
    """
    env = os.environ.copy()
    if extra_environ:
        env.update(extra_environ)

check_call(cmd, cwd=cwd, env=env)

def quiet_subprocess_runner(
    cmd: Sequence[str],
    cwd: Optional[str] = None,
    extra_environ: Optional[Mapping[str, str]] = None,
) -> None:
    """Call the subprocess while suppressing output.

This uses :func:`subprocess.check_output` under the hood.
    """
    env = os.environ.copy()
    if extra_environ:
        env.update(extra_environ)

check_output(cmd, cwd=cwd, env=env, stderr=STDOUT)

def norm_and_check(source_tree: str, requested: str) -> str:
    """Normalise and check a backend path.

Ensure that the requested backend path is specified as a relative path,
    and resolves to a location under the given source tree.

Return an absolute version of the requested path.
    """
    if os.path.isabs(requested):
        raise ValueError("paths must be relative")

abs_source = os.path.abspath(source_tree)
    abs_requested = os.path.normpath(os.path.join(abs_source, requested))
    # We have to use commonprefix for Python 2.7 compatibility. So we
    # normalise case to avoid problems because commonprefix is a character
    # based comparison :-(
    norm_source = os.path.normcase(abs_source)
    norm_requested = os.path.normcase(abs_requested)
    if os.path.commonprefix([norm_source, norm_requested]) != norm_source:
        raise ValueError("paths must be inside source tree")

return abs_requested

class BuildBackendHookCaller:
    """A wrapper to call the build backend hooks for a source directory."""

def __init__(
        self,
        source_dir: str,
        build_backend: str,
        backend_path: Optional[Sequence[str]] = None,
        runner: Optional["SubprocessRunner"] = None,
        python_executable: Optional[str] = None,
    ) -> None:
        """
        :param source_dir: The source directory to invoke the build backend for
        :param build_backend: The build backend spec
        :param backend_path: Additional path entries for the build backend spec
        :param runner: The :ref:`subprocess runner <Subprocess Runners>` to use
        :param python_executable:
            The Python executable used to invoke the build backend
        """
        if runner is None:
            runner = default_subprocess_runner

self.source_dir = abspath(source_dir)
        self.build_backend = build_backend
        if backend_path:
            backend_path = [norm_and_check(self.source_dir, p) for p in backend_path]
        self.backend_path = backend_path
        self._subprocess_runner = runner
        if not python_executable:
            python_executable = sys.executable
        self.python_executable = python_executable

@contextmanager
    def subprocess_runner(self, runner: "SubprocessRunner") -> Iterator[None]:
        """A context manager for temporarily overriding the default
        :ref:`subprocess runner <Subprocess Runners>`.

:param runner: The new subprocess runner to use within the context.

.. code-block:: python

hook_caller = BuildBackendHookCaller(...)
            with hook_caller.subprocess_runner(quiet_subprocess_runner):
                ...
        """
        prev = self._subprocess_runner
        self._subprocess_runner = runner
        try:
            yield
        finally:
            self._subprocess_runner = prev

def _supported_features(self) -> Sequence[str]:
        """Return the list of optional features supported by the backend."""
        return self._call_hook("_supported_features", {})

def get_requires_for_build_wheel(
        self,
        config_settings: Optional[Mapping[str, Any]] = None,
    ) -> Sequence[str]:
        """Get additional dependencies required for building a wheel.

:param config_settings: The configuration settings for the build backend
        :returns: A list of :pep:`dependency specifiers <508>`.

.. admonition:: Fallback

If the build backend does not defined a hook with this name, an
            empty list will be returned.
        """
        return self._call_hook(
            "get_requires_for_build_wheel", {"config_settings": config_settings}
        )

def prepare_metadata_for_build_wheel(
        self,
        metadata_directory: str,
        config_settings: Optional[Mapping[str, Any]] = None,
        _allow_fallback: bool = True,
    ) -> str:
        """Prepare a ``*.dist-info`` folder with metadata for this project.

:param metadata_directory: The directory to write the metadata to
        :param config_settings: The configuration settings for the build backend
        :param _allow_fallback:
            Whether to allow the fallback to building a wheel and extracting
            the metadata from it. Should be passed as a keyword argument only.

:returns: Name of the newly created subfolder within
                  ``metadata_directory``, containing the metadata.

.. admonition:: Fallback

If the build backend does not define a hook with this name and
            ``_allow_fallback`` is truthy, the backend will be asked to build a
            wheel via the ``build_wheel`` hook and the dist-info extracted from
            that will be returned.
        """
        return self._call_hook(
            "prepare_metadata_for_build_wheel",
            {
                "metadata_directory": abspath(metadata_directory),
                "config_settings": config_settings,
                "_allow_fallback": _allow_fallback,
            },
        )

def build_wheel(
        self,
        wheel_directory: str,
        config_settings: Optional[Mapping[str, Any]] = None,
        metadata_directory: Optional[str] = None,
    ) -> str:
        """Build a wheel from this project.

:param wheel_directory: The directory to write the wheel to
        :param config_settings: The configuration settings for the build backend
        :param metadata_directory: The directory to reuse existing metadata from
        :returns:
            The name of the newly created wheel within ``wheel_directory``.

.. admonition:: Interaction with fallback

If the ``build_wheel`` hook was called in the fallback for
            :meth:`prepare_metadata_for_build_wheel`, the build backend would
            not be invoked. Instead, the previously built wheel will be copied
            to ``wheel_directory`` and the name of that file will be returned.
        """
        if metadata_directory is not None:
            metadata_directory = abspath(metadata_directory)
        return self._call_hook(
            "build_wheel",
            {
                "wheel_directory": abspath(wheel_directory),
                "config_settings": config_settings,
                "metadata_directory": metadata_directory,
            },
        )

def get_requires_for_build_editable(
        self,
        config_settings: Optional[Mapping[str, Any]] = None,
    ) -> Sequence[str]:
        """Get additional dependencies required for building an editable wheel.

:param config_settings: The configuration settings for the build backend
        :returns: A list of :pep:`dependency specifiers <508>`.

.. admonition:: Fallback

If the build backend does not defined a hook with this name, an
            empty list will be returned.
        """
        return self._call_hook(
            "get_requires_for_build_editable", {"config_settings": config_settings}
        )

def prepare_metadata_for_build_editable(
        self,
        metadata_directory: str,
        config_settings: Optional[Mapping[str, Any]] = None,
        _allow_fallback: bool = True,
    ) -> Optional[str]:
        """Prepare a ``*.dist-info`` folder with metadata for this project.

.. admonition:: Fallback

If the build backend does not define a hook with this name and
            ``_allow_fallback`` is truthy, the backend will be asked to build a
            wheel via the ``build_editable`` hook and the dist-info
            extracted from that will be returned.
        """
        return self._call_hook(
            "prepare_metadata_for_build_editable",
            {
                "metadata_directory": abspath(metadata_directory),
                "config_settings": config_settings,
                "_allow_fallback": _allow_fallback,
            },
        )

def build_editable(
        self,
        wheel_directory: str,
        config_settings: Optional[Mapping[str, Any]] = None,
        metadata_directory: Optional[str] = None,
    ) -> str:
        """Build an editable wheel from this project.

.. admonition:: Interaction with fallback

If the ``build_editable`` hook was called in the fallback for
            :meth:`prepare_metadata_for_build_editable`, the build backend
            would not be invoked. Instead, the previously built wheel will be
            copied to ``wheel_directory`` and the name of that file will be
            returned.
        """
        if metadata_directory is not None:
            metadata_directory = abspath(metadata_directory)
        return self._call_hook(
            "build_editable",
            {
                "wheel_directory": abspath(wheel_directory),
                "config_settings": config_settings,
                "metadata_directory": metadata_directory,
            },
        )

def get_requires_for_build_sdist(
        self,
        config_settings: Optional[Mapping[str, Any]] = None,
    ) -> Sequence[str]:
        """Get additional dependencies required for building an sdist.

:returns: A list of :pep:`dependency specifiers <508>`.
        """
        return self._call_hook(
            "get_requires_for_build_sdist", {"config_settings": config_settings}
        )

def build_sdist(
        self,
        sdist_directory: str,
        config_settings: Optional[Mapping[str, Any]] = None,
    ) -> str:
        """Build an sdist from this project.

:returns:
            The name of the newly created sdist within ``wheel_directory``.
        """
        return self._call_hook(
            "build_sdist",
            {
                "sdist_directory": abspath(sdist_directory),
                "config_settings": config_settings,
            },
        )

def _call_hook(self, hook_name: str, kwargs: Mapping[str, Any]) -> Any:
        extra_environ = {"_PYPROJECT_HOOKS_BUILD_BACKEND": self.build_backend}

if self.backend_path:
            backend_path = os.pathsep.join(self.backend_path)
            extra_environ["_PYPROJECT_HOOKS_BACKEND_PATH"] = backend_path

with tempfile.TemporaryDirectory() as td:
            hook_input = {"kwargs": kwargs}
            write_json(hook_input, pjoin(td, "input.json"), indent=2)

# Run the hook in a subprocess
            with _in_proc_script_path() as script:
                python = self.python_executable
                self._subprocess_runner(
                    [python, abspath(str(script)), hook_name, td],
                    cwd=self.source_dir,
                    extra_environ=extra_environ,
                )

data = read_json(pjoin(td, "output.json"))
            if data.get("unsupported"):
                raise UnsupportedOperation(data.get("traceback", ""))
            if data.get("no_backend"):
                raise BackendUnavailable(
                    data.get("traceback", ""),
                    message=data.get("backend_error", ""),
                    backend_name=self.build_backend,
                    backend_path=self.backend_path,
                )
            if data.get("hook_missing"):
                raise HookMissing(data.get("missing_hook_name") or hook_name)
            return data["return_val"]

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