compat.py

"""Python version compatibility code."""
import enum
import functools
import inspect
import os
import re
import sys
from contextlib import contextmanager
from inspect import Parameter
from inspect import signature
from typing import Any
from typing import Callable
from typing import Generic
from typing import Optional
from typing import overload as overload
from typing import Tuple
from typing import TypeVar
from typing import Union

import attr

from _pytest._io.saferepr import saferepr
from _pytest.outcomes import fail
from _pytest.outcomes import TEST_OUTCOME

if sys.version_info < (3, 5, 2):
    TYPE_CHECKING = False  # type: bool
else:
    from typing import TYPE_CHECKING


if TYPE_CHECKING:
    from typing import NoReturn
    from typing import Type
    from typing_extensions import Final


_T = TypeVar("_T")
_S = TypeVar("_S")


# fmt: off
# Singleton type for NOTSET, as described in:
# https://www.python.org/dev/peps/pep-0484/#support-for-singleton-types-in-unions
class NotSetType(enum.Enum):
    token = 0
NOTSET = NotSetType.token  # type: Final # noqa: E305
# fmt: on

MODULE_NOT_FOUND_ERROR = (
    "ModuleNotFoundError" if sys.version_info[:2] >= (3, 6) else "ImportError"
)


if sys.version_info >= (3, 8):
    from importlib import metadata as importlib_metadata
else:
    import importlib_metadata  # noqa: F401


def _format_args(func: Callable[..., Any]) -> str:
    return str(signature(func))


# The type of re.compile objects is not exposed in Python.
REGEX_TYPE = type(re.compile(""))


if sys.version_info < (3, 6):

    def fspath(p):
        """os.fspath replacement, useful to point out when we should replace it by the
        real function once we drop py35."""
        return str(p)


else:
    fspath = os.fspath


def is_generator(func: object) -> bool:
    genfunc = inspect.isgeneratorfunction(func)
    return genfunc and not iscoroutinefunction(func)


def iscoroutinefunction(func: object) -> bool:
    """Return True if func is a coroutine function (a function defined with async
    def syntax, and doesn't contain yield), or a function decorated with
    @asyncio.coroutine.

    Note: copied and modified from Python 3.5's builtin couroutines.py to avoid
    importing asyncio directly, which in turns also initializes the "logging"
    module as a side-effect (see issue #8).
    """
    return inspect.iscoroutinefunction(func) or getattr(func, "_is_coroutine", False)


def is_async_function(func: object) -> bool:
    """Return True if the given function seems to be an async function or
    an async generator."""
    return iscoroutinefunction(func) or (
        sys.version_info >= (3, 6) and inspect.isasyncgenfunction(func)
    )


def getlocation(function, curdir: Optional[str] = None) -> str:
    from _pytest.pathlib import Path

    function = get_real_func(function)
    fn = Path(inspect.getfile(function))
    lineno = function.__code__.co_firstlineno
    if curdir is not None:
        try:
            relfn = fn.relative_to(curdir)
        except ValueError:
            pass
        else:
            return "%s:%d" % (relfn, lineno + 1)
    return "%s:%d" % (fn, lineno + 1)


def num_mock_patch_args(function) -> int:
    """Return number of arguments used up by mock arguments (if any)."""
    patchings = getattr(function, "patchings", None)
    if not patchings:
        return 0

    mock_sentinel = getattr(sys.modules.get("mock"), "DEFAULT", object())
    ut_mock_sentinel = getattr(sys.modules.get("unittest.mock"), "DEFAULT", object())

    return len(
        [
            p
            for p in patchings
            if not p.attribute_name
            and (p.new is mock_sentinel or p.new is ut_mock_sentinel)
        ]
    )


def getfuncargnames(
    function: Callable[..., Any],
    *,
    name: str = "",
    is_method: bool = False,
    cls: Optional[type] = None
) -> Tuple[str, ...]:
    """Return the names of a function's mandatory arguments.

    Should return the names of all function arguments that:
    * Aren't bound to an instance or type as in instance or class methods.
    * Don't have default values.
    * Aren't bound with functools.partial.
    * Aren't replaced with mocks.

    The is_method and cls arguments indicate that the function should
    be treated as a bound method even though it's not unless, only in
    the case of cls, the function is a static method.

    The name parameter should be the original name in which the function was collected.
    """
    # TODO(RonnyPfannschmidt): This function should be refactored when we
    # revisit fixtures. The fixture mechanism should ask the node for
    # the fixture names, and not try to obtain directly from the
    # function object well after collection has occurred.

    # The parameters attribute of a Signature object contains an
    # ordered mapping of parameter names to Parameter instances.  This
    # creates a tuple of the names of the parameters that don't have
    # defaults.
    try:
        parameters = signature(function).parameters
    except (ValueError, TypeError) as e:
        fail(
            "Could not determine arguments of {!r}: {}".format(function, e),
            pytrace=False,
        )

    arg_names = tuple(
        p.name
        for p in parameters.values()
        if (
            # TODO: Remove type ignore after https://github.com/python/typeshed/pull/4383
            p.kind is Parameter.POSITIONAL_OR_KEYWORD  # type: ignore[unreachable]
            or p.kind is Parameter.KEYWORD_ONLY  # type: ignore[unreachable]
        )
        and p.default is Parameter.empty
    )
    if not name:
        name = function.__name__

    # If this function should be treated as a bound method even though
    # it's passed as an unbound method or function, remove the first
    # parameter name.
    if is_method or (
        cls and not isinstance(cls.__dict__.get(name, None), staticmethod)
    ):
        arg_names = arg_names[1:]
    # Remove any names that will be replaced with mocks.
    if hasattr(function, "__wrapped__"):
        arg_names = arg_names[num_mock_patch_args(function) :]
    return arg_names


if sys.version_info < (3, 7):

    @contextmanager
    def nullcontext():
        yield


else:
    from contextlib import nullcontext as nullcontext  # noqa: F401


def get_default_arg_names(function: Callable[..., Any]) -> Tuple[str, ...]:
    # Note: this code intentionally mirrors the code at the beginning of
    # getfuncargnames, to get the arguments which were excluded from its result
    # because they had default values.
    return tuple(
        p.name
        for p in signature(function).parameters.values()
        if p.kind in (Parameter.POSITIONAL_OR_KEYWORD, Parameter.KEYWORD_ONLY)
        and p.default is not Parameter.empty
    )


_non_printable_ascii_translate_table = {
    i: "\\x{:02x}".format(i) for i in range(128) if i not in range(32, 127)
}
_non_printable_ascii_translate_table.update(
    {ord("\t"): "\\t", ord("\r"): "\\r", ord("\n"): "\\n"}
)


def _translate_non_printable(s: str) -> str:
    return s.translate(_non_printable_ascii_translate_table)


STRING_TYPES = bytes, str


def _bytes_to_ascii(val: bytes) -> str:
    return val.decode("ascii", "backslashreplace")


def ascii_escaped(val: Union[bytes, str]) -> str:
    r"""If val is pure ASCII, return it as an str, otherwise, escape
    bytes objects into a sequence of escaped bytes:

    b'\xc3\xb4\xc5\xd6' -> r'\xc3\xb4\xc5\xd6'

    and escapes unicode objects into a sequence of escaped unicode
    ids, e.g.:

    r'4\nV\U00043efa\x0eMXWB\x1e\u3028\u15fd\xcd\U0007d944'

    Note:
       The obvious "v.decode('unicode-escape')" will return
       valid UTF-8 unicode if it finds them in bytes, but we
       want to return escaped bytes for any byte, even if they match
       a UTF-8 string.
    """
    if isinstance(val, bytes):
        ret = _bytes_to_ascii(val)
    else:
        ret = val.encode("unicode_escape").decode("ascii")
    return _translate_non_printable(ret)


@attr.s
class _PytestWrapper:
    """Dummy wrapper around a function object for internal use only.

    Used to correctly unwrap the underlying function object when we are
    creating fixtures, because we wrap the function object ourselves with a
    decorator to issue warnings when the fixture function is called directly.
    """

    obj = attr.ib()


def get_real_func(obj):
    """Get the real function object of the (possibly) wrapped object by
    functools.wraps or functools.partial."""
    start_obj = obj
    for i in range(100):
        # __pytest_wrapped__ is set by @pytest.fixture when wrapping the fixture function
        # to trigger a warning if it gets called directly instead of by pytest: we don't
        # want to unwrap further than this otherwise we lose useful wrappings like @mock.patch (#3774)
        new_obj = getattr(obj, "__pytest_wrapped__", None)
        if isinstance(new_obj, _PytestWrapper):
            obj = new_obj.obj
            break
        new_obj = getattr(obj, "__wrapped__", None)
        if new_obj is None:
            break
        obj = new_obj
    else:
        raise ValueError(
            ("could not find real function of {start}\nstopped at {current}").format(
                start=saferepr(start_obj), current=saferepr(obj)
            )
        )
    if isinstance(obj, functools.partial):
        obj = obj.func
    return obj


def get_real_method(obj, holder):
    """Attempt to obtain the real function object that might be wrapping
    ``obj``, while at the same time returning a bound method to ``holder`` if
    the original object was a bound method."""
    try:
        is_method = hasattr(obj, "__func__")
        obj = get_real_func(obj)
    except Exception:  # pragma: no cover
        return obj
    if is_method and hasattr(obj, "__get__") and callable(obj.__get__):
        obj = obj.__get__(holder)
    return obj


def getimfunc(func):
    try:
        return func.__func__
    except AttributeError:
        return func


def safe_getattr(object: Any, name: str, default: Any) -> Any:
    """Like getattr but return default upon any Exception or any OutcomeException.

    Attribute access can potentially fail for 'evil' Python objects.
    See issue #214.
    It catches OutcomeException because of #2490 (issue #580), new outcomes
    are derived from BaseException instead of Exception (for more details
    check #2707).
    """
    try:
        return getattr(object, name, default)
    except TEST_OUTCOME:
        return default


def safe_isclass(obj: object) -> bool:
    """Ignore any exception via isinstance on Python 3."""
    try:
        return inspect.isclass(obj)
    except Exception:
        return False


if sys.version_info < (3, 5, 2):

    def overload(f):  # noqa: F811
        return f


if getattr(attr, "__version_info__", ()) >= (19, 2):
    ATTRS_EQ_FIELD = "eq"
else:
    ATTRS_EQ_FIELD = "cmp"


if sys.version_info >= (3, 8):
    from functools import cached_property as cached_property
else:

    class cached_property(Generic[_S, _T]):
        __slots__ = ("func", "__doc__")

        def __init__(self, func: Callable[[_S], _T]) -> None:
            self.func = func
            self.__doc__ = func.__doc__

        @overload
        def __get__(
            self, instance: None, owner: Optional["Type[_S]"] = ...
        ) -> "cached_property[_S, _T]":
            ...

        @overload  # noqa: F811
        def __get__(  # noqa: F811
            self, instance: _S, owner: Optional["Type[_S]"] = ...
        ) -> _T:
            ...

        def __get__(self, instance, owner=None):  # noqa: F811
            if instance is None:
                return self
            value = instance.__dict__[self.func.__name__] = self.func(instance)
            return value


# Sometimes an algorithm needs a dict which yields items in the order in which
# they were inserted when iterated. Since Python 3.7, `dict` preserves
# insertion order. Since `dict` is faster and uses less memory than
# `OrderedDict`, prefer to use it if possible.
if sys.version_info >= (3, 7):
    order_preserving_dict = dict
else:
    from collections import OrderedDict

    order_preserving_dict = OrderedDict


# Perform exhaustiveness checking.
#
# Consider this example:
#
#     MyUnion = Union[int, str]
#
#     def handle(x: MyUnion) -> int {
#         if isinstance(x, int):
#             return 1
#         elif isinstance(x, str):
#             return 2
#         else:
#             raise Exception('unreachable')
#
# Now suppose we add a new variant:
#
#     MyUnion = Union[int, str, bytes]
#
# After doing this, we must remember ourselves to go and update the handle
# function to handle the new variant.
#
# With `assert_never` we can do better:
#
#     // raise Exception('unreachable')
#     return assert_never(x)
#
# Now, if we forget to handle the new variant, the type-checker will emit a
# compile-time error, instead of the runtime error we would have gotten
# previously.
#
# This also work for Enums (if you use `is` to compare) and Literals.
def assert_never(value: "NoReturn") -> "NoReturn":
    assert False, "Unhandled value: {} ({})".format(value, type(value).__name__)