monkeypatch.py

"""Monkeypatching and mocking functionality."""
import os
import re
import sys
import warnings
from contextlib import contextmanager
from typing import Any
from typing import Generator
from typing import List
from typing import MutableMapping
from typing import Optional
from typing import Tuple
from typing import TypeVar
from typing import Union

import pytest
from _pytest.compat import overload
from _pytest.fixtures import fixture
from _pytest.pathlib import Path

RE_IMPORT_ERROR_NAME = re.compile(r"^No module named (.*)$")


K = TypeVar("K")
V = TypeVar("V")


@fixture
def monkeypatch() -> Generator["MonkeyPatch", None, None]:
    """A convenient fixture for monkey-patching.

    The fixture provides these methods to modify objects, dictionaries or
    os.environ::

        monkeypatch.setattr(obj, name, value, raising=True)
        monkeypatch.delattr(obj, name, raising=True)
        monkeypatch.setitem(mapping, name, value)
        monkeypatch.delitem(obj, name, raising=True)
        monkeypatch.setenv(name, value, prepend=False)
        monkeypatch.delenv(name, raising=True)
        monkeypatch.syspath_prepend(path)
        monkeypatch.chdir(path)

    All modifications will be undone after the requesting test function or
    fixture has finished. The ``raising`` parameter determines if a KeyError
    or AttributeError will be raised if the set/deletion operation has no target.
    """
    mpatch = MonkeyPatch()
    yield mpatch
    mpatch.undo()


def resolve(name: str) -> object:
    # Simplified from zope.dottedname.
    parts = name.split(".")

    used = parts.pop(0)
    found = __import__(used)
    for part in parts:
        used += "." + part
        try:
            found = getattr(found, part)
        except AttributeError:
            pass
        else:
            continue
        # We use explicit un-nesting of the handling block in order
        # to avoid nested exceptions.
        try:
            __import__(used)
        except ImportError as ex:
            expected = str(ex).split()[-1]
            if expected == used:
                raise
            else:
                raise ImportError("import error in {}: {}".format(used, ex)) from ex
        found = annotated_getattr(found, part, used)
    return found


def annotated_getattr(obj: object, name: str, ann: str) -> object:
    try:
        obj = getattr(obj, name)
    except AttributeError as e:
        raise AttributeError(
            "{!r} object at {} has no attribute {!r}".format(
                type(obj).__name__, ann, name
            )
        ) from e
    return obj


def derive_importpath(import_path: str, raising: bool) -> Tuple[str, object]:
    if not isinstance(import_path, str) or "." not in import_path:  # type: ignore[unreachable]
        raise TypeError(
            "must be absolute import path string, not {!r}".format(import_path)
        )
    module, attr = import_path.rsplit(".", 1)
    target = resolve(module)
    if raising:
        annotated_getattr(target, attr, ann=module)
    return attr, target


class Notset:
    def __repr__(self) -> str:
        return "<notset>"


notset = Notset()


class MonkeyPatch:
    """Object returned by the ``monkeypatch`` fixture keeping a record of
    setattr/item/env/syspath changes."""

    def __init__(self) -> None:
        self._setattr = []  # type: List[Tuple[object, str, object]]
        self._setitem = (
            []
        )  # type: List[Tuple[MutableMapping[Any, Any], object, object]]
        self._cwd = None  # type: Optional[str]
        self._savesyspath = None  # type: Optional[List[str]]

    @contextmanager
    def context(self) -> Generator["MonkeyPatch", None, None]:
        """Context manager that returns a new :class:`MonkeyPatch` object
        which undoes any patching done inside the ``with`` block upon exit.

        Example:

        .. code-block:: python

            import functools


            def test_partial(monkeypatch):
                with monkeypatch.context() as m:
                    m.setattr(functools, "partial", 3)

        Useful in situations where it is desired to undo some patches before the test ends,
        such as mocking ``stdlib`` functions that might break pytest itself if mocked (for examples
        of this see `#3290 <https://github.com/pytest-dev/pytest/issues/3290>`_.
        """
        m = MonkeyPatch()
        try:
            yield m
        finally:
            m.undo()

    @overload
    def setattr(
        self, target: str, name: object, value: Notset = ..., raising: bool = ...,
    ) -> None:
        ...

    @overload  # noqa: F811
    def setattr(  # noqa: F811
        self, target: object, name: str, value: object, raising: bool = ...,
    ) -> None:
        ...

    def setattr(  # noqa: F811
        self,
        target: Union[str, object],
        name: Union[object, str],
        value: object = notset,
        raising: bool = True,
    ) -> None:
        """Set attribute value on target, memorizing the old value.

        For convenience you can specify a string as ``target`` which
        will be interpreted as a dotted import path, with the last part
        being the attribute name. For example,
        ``monkeypatch.setattr("os.getcwd", lambda: "/")``
        would set the ``getcwd`` function of the ``os`` module.

        Raises AttributeError if the attribute does not exist, unless
        ``raising`` is set to False.
        """
        __tracebackhide__ = True
        import inspect

        if isinstance(value, Notset):
            if not isinstance(target, str):
                raise TypeError(
                    "use setattr(target, name, value) or "
                    "setattr(target, value) with target being a dotted "
                    "import string"
                )
            value = name
            name, target = derive_importpath(target, raising)
        else:
            if not isinstance(name, str):
                raise TypeError(
                    "use setattr(target, name, value) with name being a string or "
                    "setattr(target, value) with target being a dotted "
                    "import string"
                )

        oldval = getattr(target, name, notset)
        if raising and oldval is notset:
            raise AttributeError("{!r} has no attribute {!r}".format(target, name))

        # avoid class descriptors like staticmethod/classmethod
        if inspect.isclass(target):
            oldval = target.__dict__.get(name, notset)
        self._setattr.append((target, name, oldval))
        setattr(target, name, value)

    def delattr(
        self,
        target: Union[object, str],
        name: Union[str, Notset] = notset,
        raising: bool = True,
    ) -> None:
        """Delete attribute ``name`` from ``target``.

        If no ``name`` is specified and ``target`` is a string
        it will be interpreted as a dotted import path with the
        last part being the attribute name.

        Raises AttributeError it the attribute does not exist, unless
        ``raising`` is set to False.
        """
        __tracebackhide__ = True
        import inspect

        if isinstance(name, Notset):
            if not isinstance(target, str):
                raise TypeError(
                    "use delattr(target, name) or "
                    "delattr(target) with target being a dotted "
                    "import string"
                )
            name, target = derive_importpath(target, raising)

        if not hasattr(target, name):
            if raising:
                raise AttributeError(name)
        else:
            oldval = getattr(target, name, notset)
            # Avoid class descriptors like staticmethod/classmethod.
            if inspect.isclass(target):
                oldval = target.__dict__.get(name, notset)
            self._setattr.append((target, name, oldval))
            delattr(target, name)

    def setitem(self, dic: MutableMapping[K, V], name: K, value: V) -> None:
        """Set dictionary entry ``name`` to value."""
        self._setitem.append((dic, name, dic.get(name, notset)))
        dic[name] = value

    def delitem(self, dic: MutableMapping[K, V], name: K, raising: bool = True) -> None:
        """Delete ``name`` from dict.

        Raises ``KeyError`` if it doesn't exist, unless ``raising`` is set to
        False.
        """
        if name not in dic:
            if raising:
                raise KeyError(name)
        else:
            self._setitem.append((dic, name, dic.get(name, notset)))
            del dic[name]

    def setenv(self, name: str, value: str, prepend: Optional[str] = None) -> None:
        """Set environment variable ``name`` to ``value``.

        If ``prepend`` is a character, read the current environment variable
        value and prepend the ``value`` adjoined with the ``prepend``
        character.
        """
        if not isinstance(value, str):
            warnings.warn(  # type: ignore[unreachable]
                pytest.PytestWarning(
                    "Value of environment variable {name} type should be str, but got "
                    "{value!r} (type: {type}); converted to str implicitly".format(
                        name=name, value=value, type=type(value).__name__
                    )
                ),
                stacklevel=2,
            )
            value = str(value)
        if prepend and name in os.environ:
            value = value + prepend + os.environ[name]
        self.setitem(os.environ, name, value)

    def delenv(self, name: str, raising: bool = True) -> None:
        """Delete ``name`` from the environment.

        Raises ``KeyError`` if it does not exist, unless ``raising`` is set to
        False.
        """
        environ = os.environ  # type: MutableMapping[str, str]
        self.delitem(environ, name, raising=raising)

    def syspath_prepend(self, path) -> None:
        """Prepend ``path`` to ``sys.path`` list of import locations."""
        from pkg_resources import fixup_namespace_packages

        if self._savesyspath is None:
            self._savesyspath = sys.path[:]
        sys.path.insert(0, str(path))

        # https://github.com/pypa/setuptools/blob/d8b901bc/docs/pkg_resources.txt#L162-L171
        fixup_namespace_packages(str(path))

        # A call to syspathinsert() usually means that the caller wants to
        # import some dynamically created files, thus with python3 we
        # invalidate its import caches.
        # This is especially important when any namespace package is in use,
        # since then the mtime based FileFinder cache (that gets created in
        # this case already) gets not invalidated when writing the new files
        # quickly afterwards.
        from importlib import invalidate_caches

        invalidate_caches()

    def chdir(self, path) -> None:
        """Change the current working directory to the specified path.

        Path can be a string or a py.path.local object.
        """
        if self._cwd is None:
            self._cwd = os.getcwd()
        if hasattr(path, "chdir"):
            path.chdir()
        elif isinstance(path, Path):
            # Modern python uses the fspath protocol here LEGACY
            os.chdir(str(path))
        else:
            os.chdir(path)

    def undo(self) -> None:
        """Undo previous changes.

        This call consumes the undo stack. Calling it a second time has no
        effect unless you do more monkeypatching after the undo call.

        There is generally no need to call `undo()`, since it is
        called automatically during tear-down.

        Note that the same `monkeypatch` fixture is used across a
        single test function invocation. If `monkeypatch` is used both by
        the test function itself and one of the test fixtures,
        calling `undo()` will undo all of the changes made in
        both functions.
        """
        for obj, name, value in reversed(self._setattr):
            if value is not notset:
                setattr(obj, name, value)
            else:
                delattr(obj, name)
        self._setattr[:] = []
        for dictionary, key, value in reversed(self._setitem):
            if value is notset:
                try:
                    del dictionary[key]
                except KeyError:
                    pass  # Was already deleted, so we have the desired state.
            else:
                dictionary[key] = value
        self._setitem[:] = []
        if self._savesyspath is not None:
            sys.path[:] = self._savesyspath
            self._savesyspath = None

        if self._cwd is not None:
            os.chdir(self._cwd)
            self._cwd = None