__init__.py

"""
    sphinx.ext.autodoc
    ~~~~~~~~~~~~~~~~~~

    Automatically insert docstrings for functions, classes or whole modules into
    the doctree, thus avoiding duplication between docstrings and documentation
    for those who like elaborate docstrings.

    :copyright: Copyright 2007-2021 by the Sphinx team, see AUTHORS.
    :license: BSD, see LICENSE for details.
"""

import re
import warnings
from inspect import Parameter, Signature
from types import ModuleType
from typing import (TYPE_CHECKING, Any, Callable, Dict, Iterator, List, Optional, Sequence,
                    Set, Tuple, Type, TypeVar, Union)

from docutils.statemachine import StringList

import sphinx
from sphinx.application import Sphinx
from sphinx.config import ENUM, Config
from sphinx.deprecation import RemovedInSphinx50Warning, RemovedInSphinx60Warning
from sphinx.environment import BuildEnvironment
from sphinx.ext.autodoc.importer import (get_class_members, get_object_members, import_module,
                                         import_object)
from sphinx.ext.autodoc.mock import ismock, mock, undecorate
from sphinx.locale import _, __
from sphinx.pycode import ModuleAnalyzer, PycodeError
from sphinx.util import inspect, logging
from sphinx.util.docstrings import prepare_docstring, separate_metadata
from sphinx.util.inspect import (evaluate_signature, getdoc, object_description, safe_getattr,
                                 stringify_signature)
from sphinx.util.typing import OptionSpec, get_type_hints, restify
from sphinx.util.typing import stringify as stringify_typehint

if TYPE_CHECKING:
    from sphinx.ext.autodoc.directive import DocumenterBridge


logger = logging.getLogger(__name__)


# This type isn't exposed directly in any modules, but can be found
# here in most Python versions
MethodDescriptorType = type(type.__subclasses__)


#: extended signature RE: with explicit module name separated by ::
py_ext_sig_re = re.compile(
    r'''^ ([\w.]+::)?            # explicit module name
          ([\w.]+\.)?            # module and/or class name(s)
          (\w+)  \s*             # thing name
          (?: \((.*)\)           # optional: arguments
           (?:\s* -> \s* (.*))?  #           return annotation
          )? $                   # and nothing more
          ''', re.VERBOSE)
special_member_re = re.compile(r'^__\S+__$')


def identity(x: Any) -> Any:
    return x


class _All:
    """A special value for :*-members: that matches to any member."""

    def __contains__(self, item: Any) -> bool:
        return True

    def append(self, item: Any) -> None:
        pass  # nothing


class _Empty:
    """A special value for :exclude-members: that never matches to any member."""

    def __contains__(self, item: Any) -> bool:
        return False


ALL = _All()
EMPTY = _Empty()
UNINITIALIZED_ATTR = object()
INSTANCEATTR = object()
SLOTSATTR = object()


def members_option(arg: Any) -> Union[object, List[str]]:
    """Used to convert the :members: option to auto directives."""
    if arg in (None, True):
        return ALL
    elif arg is False:
        return None
    else:
        return [x.strip() for x in arg.split(',') if x.strip()]


def members_set_option(arg: Any) -> Union[object, Set[str]]:
    """Used to convert the :members: option to auto directives."""
    warnings.warn("members_set_option() is deprecated.",
                  RemovedInSphinx50Warning, stacklevel=2)
    if arg is None:
        return ALL
    return {x.strip() for x in arg.split(',') if x.strip()}


def exclude_members_option(arg: Any) -> Union[object, Set[str]]:
    """Used to convert the :exclude-members: option."""
    if arg in (None, True):
        return EMPTY
    return {x.strip() for x in arg.split(',') if x.strip()}


def inherited_members_option(arg: Any) -> Union[object, Set[str]]:
    """Used to convert the :members: option to auto directives."""
    if arg in (None, True):
        return 'object'
    else:
        return arg


def member_order_option(arg: Any) -> Optional[str]:
    """Used to convert the :members: option to auto directives."""
    if arg in (None, True):
        return None
    elif arg in ('alphabetical', 'bysource', 'groupwise'):
        return arg
    else:
        raise ValueError(__('invalid value for member-order option: %s') % arg)


def class_doc_from_option(arg: Any) -> Optional[str]:
    """Used to convert the :class-doc-from: option to autoclass directives."""
    if arg in ('both', 'class', 'init'):
        return arg
    else:
        raise ValueError(__('invalid value for class-doc-from option: %s') % arg)


SUPPRESS = object()


def annotation_option(arg: Any) -> Any:
    if arg in (None, True):
        # suppress showing the representation of the object
        return SUPPRESS
    else:
        return arg


def bool_option(arg: Any) -> bool:
    """Used to convert flag options to auto directives.  (Instead of
    directives.flag(), which returns None).
    """
    return True


def merge_special_members_option(options: Dict) -> None:
    """Merge :special-members: option to :members: option."""
    warnings.warn("merge_special_members_option() is deprecated.",
                  RemovedInSphinx50Warning, stacklevel=2)
    if 'special-members' in options and options['special-members'] is not ALL:
        if options.get('members') is ALL:
            pass
        elif options.get('members'):
            for member in options['special-members']:
                if member not in options['members']:
                    options['members'].append(member)
        else:
            options['members'] = options['special-members']


def merge_members_option(options: Dict) -> None:
    """Merge :*-members: option to the :members: option."""
    if options.get('members') is ALL:
        # merging is not needed when members: ALL
        return

    members = options.setdefault('members', [])
    for key in {'private-members', 'special-members'}:
        if key in options and options[key] not in (ALL, None):
            for member in options[key]:
                if member not in members:
                    members.append(member)


# Some useful event listener factories for autodoc-process-docstring.

def cut_lines(pre: int, post: int = 0, what: str = None) -> Callable:
    """Return a listener that removes the first *pre* and last *post*
    lines of every docstring.  If *what* is a sequence of strings,
    only docstrings of a type in *what* will be processed.

    Use like this (e.g. in the ``setup()`` function of :file:`conf.py`)::

       from sphinx.ext.autodoc import cut_lines
       app.connect('autodoc-process-docstring', cut_lines(4, what=['module']))

    This can (and should) be used in place of :confval:`automodule_skip_lines`.
    """
    def process(app: Sphinx, what_: str, name: str, obj: Any, options: Any, lines: List[str]
                ) -> None:
        if what and what_ not in what:
            return
        del lines[:pre]
        if post:
            # remove one trailing blank line.
            if lines and not lines[-1]:
                lines.pop(-1)
            del lines[-post:]
        # make sure there is a blank line at the end
        if lines and lines[-1]:
            lines.append('')
    return process


def between(marker: str, what: Sequence[str] = None, keepempty: bool = False,
            exclude: bool = False) -> Callable:
    """Return a listener that either keeps, or if *exclude* is True excludes,
    lines between lines that match the *marker* regular expression.  If no line
    matches, the resulting docstring would be empty, so no change will be made
    unless *keepempty* is true.

    If *what* is a sequence of strings, only docstrings of a type in *what* will
    be processed.
    """
    marker_re = re.compile(marker)

    def process(app: Sphinx, what_: str, name: str, obj: Any, options: Any, lines: List[str]
                ) -> None:
        if what and what_ not in what:
            return
        deleted = 0
        delete = not exclude
        orig_lines = lines[:]
        for i, line in enumerate(orig_lines):
            if delete:
                lines.pop(i - deleted)
                deleted += 1
            if marker_re.match(line):
                delete = not delete
                if delete:
                    lines.pop(i - deleted)
                    deleted += 1
        if not lines and not keepempty:
            lines[:] = orig_lines
        # make sure there is a blank line at the end
        if lines and lines[-1]:
            lines.append('')
    return process


# This class is used only in ``sphinx.ext.autodoc.directive``,
# But we define this class here to keep compatibility (see #4538)
class Options(dict):
    """A dict/attribute hybrid that returns None on nonexisting keys."""
    def copy(self) -> "Options":
        return Options(super())

    def __getattr__(self, name: str) -> Any:
        try:
            return self[name.replace('_', '-')]
        except KeyError:
            return None


class ObjectMember(tuple):
    """A member of object.

    This is used for the result of `Documenter.get_object_members()` to
    represent each member of the object.

    .. Note::

       An instance of this class behaves as a tuple of (name, object)
       for compatibility to old Sphinx.  The behavior will be dropped
       in the future.  Therefore extensions should not use the tuple
       interface.
    """

    def __new__(cls, name: str, obj: Any, **kwargs: Any) -> Any:
        return super().__new__(cls, (name, obj))  # type: ignore

    def __init__(self, name: str, obj: Any, docstring: Optional[str] = None,
                 class_: Any = None, skipped: bool = False) -> None:
        self.__name__ = name
        self.object = obj
        self.docstring = docstring
        self.skipped = skipped
        self.class_ = class_


ObjectMembers = Union[List[ObjectMember], List[Tuple[str, Any]]]


class Documenter:
    """
    A Documenter knows how to autodocument a single object type.  When
    registered with the AutoDirective, it will be used to document objects
    of that type when needed by autodoc.

    Its *objtype* attribute selects what auto directive it is assigned to
    (the directive name is 'auto' + objtype), and what directive it generates
    by default, though that can be overridden by an attribute called
    *directivetype*.

    A Documenter has an *option_spec* that works like a docutils directive's;
    in fact, it will be used to parse an auto directive's options that matches
    the documenter.
    """
    #: name by which the directive is called (auto...) and the default
    #: generated directive name
    objtype = 'object'
    #: indentation by which to indent the directive content
    content_indent = '   '
    #: priority if multiple documenters return True from can_document_member
    priority = 0
    #: order if autodoc_member_order is set to 'groupwise'
    member_order = 0
    #: true if the generated content may contain titles
    titles_allowed = False

    option_spec: OptionSpec = {
        'noindex': bool_option
    }

    def get_attr(self, obj: Any, name: str, *defargs: Any) -> Any:
        """getattr() override for types such as Zope interfaces."""
        return autodoc_attrgetter(self.env.app, obj, name, *defargs)

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        """Called to see if a member can be documented by this documenter."""
        raise NotImplementedError('must be implemented in subclasses')

    def __init__(self, directive: "DocumenterBridge", name: str, indent: str = '') -> None:
        self.directive = directive
        self.config: Config = directive.env.config
        self.env: BuildEnvironment = directive.env
        self.options = directive.genopt
        self.name = name
        self.indent = indent
        # the module and object path within the module, and the fully
        # qualified name (all set after resolve_name succeeds)
        self.modname: str = None
        self.module: ModuleType = None
        self.objpath: List[str] = None
        self.fullname: str = None
        # extra signature items (arguments and return annotation,
        # also set after resolve_name succeeds)
        self.args: str = None
        self.retann: str = None
        # the object to document (set after import_object succeeds)
        self.object: Any = None
        self.object_name: str = None
        # the parent/owner of the object to document
        self.parent: Any = None
        # the module analyzer to get at attribute docs, or None
        self.analyzer: ModuleAnalyzer = None

    @property
    def documenters(self) -> Dict[str, Type["Documenter"]]:
        """Returns registered Documenter classes"""
        return self.env.app.registry.documenters

    def add_line(self, line: str, source: str, *lineno: int) -> None:
        """Append one line of generated reST to the output."""
        if line.strip():  # not a blank line
            self.directive.result.append(self.indent + line, source, *lineno)
        else:
            self.directive.result.append('', source, *lineno)

    def resolve_name(self, modname: str, parents: Any, path: str, base: Any
                     ) -> Tuple[str, List[str]]:
        """Resolve the module and name of the object to document given by the
        arguments and the current module/class.

        Must return a pair of the module name and a chain of attributes; for
        example, it would return ``('zipfile', ['ZipFile', 'open'])`` for the
        ``zipfile.ZipFile.open`` method.
        """
        raise NotImplementedError('must be implemented in subclasses')

    def parse_name(self) -> bool:
        """Determine what module to import and what attribute to document.

        Returns True and sets *self.modname*, *self.objpath*, *self.fullname*,
        *self.args* and *self.retann* if parsing and resolving was successful.
        """
        # first, parse the definition -- auto directives for classes and
        # functions can contain a signature which is then used instead of
        # an autogenerated one
        try:
            matched = py_ext_sig_re.match(self.name)
            explicit_modname, path, base, args, retann = matched.groups()
        except AttributeError:
            logger.warning(__('invalid signature for auto%s (%r)') % (self.objtype, self.name),
                           type='autodoc')
            return False

        # support explicit module and class name separation via ::
        if explicit_modname is not None:
            modname = explicit_modname[:-2]
            parents = path.rstrip('.').split('.') if path else []
        else:
            modname = None
            parents = []

        with mock(self.config.autodoc_mock_imports):
            self.modname, self.objpath = self.resolve_name(modname, parents, path, base)

        if not self.modname:
            return False

        self.args = args
        self.retann = retann
        self.fullname = ((self.modname or '') +
                         ('.' + '.'.join(self.objpath) if self.objpath else ''))
        return True

    def import_object(self, raiseerror: bool = False) -> bool:
        """Import the object given by *self.modname* and *self.objpath* and set
        it as *self.object*.

        Returns True if successful, False if an error occurred.
        """
        with mock(self.config.autodoc_mock_imports):
            try:
                ret = import_object(self.modname, self.objpath, self.objtype,
                                    attrgetter=self.get_attr,
                                    warningiserror=self.config.autodoc_warningiserror)
                self.module, self.parent, self.object_name, self.object = ret
                if ismock(self.object):
                    self.object = undecorate(self.object)
                return True
            except ImportError as exc:
                if raiseerror:
                    raise
                else:
                    logger.warning(exc.args[0], type='autodoc', subtype='import_object')
                    self.env.note_reread()
                    return False

    def get_real_modname(self) -> str:
        """Get the real module name of an object to document.

        It can differ from the name of the module through which the object was
        imported.
        """
        return self.get_attr(self.object, '__module__', None) or self.modname

    def check_module(self) -> bool:
        """Check if *self.object* is really defined in the module given by
        *self.modname*.
        """
        if self.options.imported_members:
            return True

        subject = inspect.unpartial(self.object)
        modname = self.get_attr(subject, '__module__', None)
        if modname and modname != self.modname:
            return False
        return True

    def format_args(self, **kwargs: Any) -> str:
        """Format the argument signature of *self.object*.

        Should return None if the object does not have a signature.
        """
        return None

    def format_name(self) -> str:
        """Format the name of *self.object*.

        This normally should be something that can be parsed by the generated
        directive, but doesn't need to be (Sphinx will display it unparsed
        then).
        """
        # normally the name doesn't contain the module (except for module
        # directives of course)
        return '.'.join(self.objpath) or self.modname

    def _call_format_args(self, **kwargs: Any) -> str:
        if kwargs:
            try:
                return self.format_args(**kwargs)
            except TypeError:
                # avoid chaining exceptions, by putting nothing here
                pass

        # retry without arguments for old documenters
        return self.format_args()

    def format_signature(self, **kwargs: Any) -> str:
        """Format the signature (arguments and return annotation) of the object.

        Let the user process it via the ``autodoc-process-signature`` event.
        """
        if self.args is not None:
            # signature given explicitly
            args = "(%s)" % self.args
            retann = self.retann
        else:
            # try to introspect the signature
            try:
                retann = None
                args = self._call_format_args(**kwargs)
                if args:
                    matched = re.match(r'^(\(.*\))\s+->\s+(.*)$', args)
                    if matched:
                        args = matched.group(1)
                        retann = matched.group(2)
            except Exception as exc:
                logger.warning(__('error while formatting arguments for %s: %s'),
                               self.fullname, exc, type='autodoc')
                args = None

        result = self.env.events.emit_firstresult('autodoc-process-signature',
                                                  self.objtype, self.fullname,
                                                  self.object, self.options, args, retann)
        if result:
            args, retann = result

        if args is not None:
            return args + ((' -> %s' % retann) if retann else '')
        else:
            return ''

    def add_directive_header(self, sig: str) -> None:
        """Add the directive header and options to the generated content."""
        domain = getattr(self, 'domain', 'py')
        directive = getattr(self, 'directivetype', self.objtype)
        name = self.format_name()
        sourcename = self.get_sourcename()

        # one signature per line, indented by column
        prefix = '.. %s:%s:: ' % (domain, directive)
        for i, sig_line in enumerate(sig.split("\n")):
            self.add_line('%s%s%s' % (prefix, name, sig_line),
                          sourcename)
            if i == 0:
                prefix = " " * len(prefix)

        if self.options.noindex:
            self.add_line('   :noindex:', sourcename)
        if self.objpath:
            # Be explicit about the module, this is necessary since .. class::
            # etc. don't support a prepended module name
            self.add_line('   :module: %s' % self.modname, sourcename)

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        """Decode and return lines of the docstring(s) for the object.

        When it returns None value, autodoc-process-docstring will not be called for this
        object.
        """
        if ignore is not None:
            warnings.warn("The 'ignore' argument to autodoc.%s.get_doc() is deprecated."
                          % self.__class__.__name__,
                          RemovedInSphinx50Warning, stacklevel=2)
        docstring = getdoc(self.object, self.get_attr, self.config.autodoc_inherit_docstrings,
                           self.parent, self.object_name)
        if docstring:
            tab_width = self.directive.state.document.settings.tab_width
            return [prepare_docstring(docstring, ignore, tab_width)]
        return []

    def process_doc(self, docstrings: List[List[str]]) -> Iterator[str]:
        """Let the user process the docstrings before adding them."""
        for docstringlines in docstrings:
            if self.env.app:
                # let extensions preprocess docstrings
                self.env.app.emit('autodoc-process-docstring',
                                  self.objtype, self.fullname, self.object,
                                  self.options, docstringlines)

                if docstringlines and docstringlines[-1] != '':
                    # append a blank line to the end of the docstring
                    docstringlines.append('')

            yield from docstringlines

    def get_sourcename(self) -> str:
        if (getattr(self.object, '__module__', None) and
                getattr(self.object, '__qualname__', None)):
            # Get the correct location of docstring from self.object
            # to support inherited methods
            fullname = '%s.%s' % (self.object.__module__, self.object.__qualname__)
        else:
            fullname = self.fullname

        if self.analyzer:
            return '%s:docstring of %s' % (self.analyzer.srcname, fullname)
        else:
            return 'docstring of %s' % fullname

    def add_content(self, more_content: Optional[StringList], no_docstring: bool = False
                    ) -> None:
        """Add content from docstrings, attribute documentation and user."""
        if no_docstring:
            warnings.warn("The 'no_docstring' argument to %s.add_content() is deprecated."
                          % self.__class__.__name__,
                          RemovedInSphinx50Warning, stacklevel=2)

        # set sourcename and add content from attribute documentation
        sourcename = self.get_sourcename()
        if self.analyzer:
            attr_docs = self.analyzer.find_attr_docs()
            if self.objpath:
                key = ('.'.join(self.objpath[:-1]), self.objpath[-1])
                if key in attr_docs:
                    no_docstring = True
                    # make a copy of docstring for attributes to avoid cache
                    # the change of autodoc-process-docstring event.
                    docstrings = [list(attr_docs[key])]

                    for i, line in enumerate(self.process_doc(docstrings)):
                        self.add_line(line, sourcename, i)

        # add content from docstrings
        if not no_docstring:
            docstrings = self.get_doc()
            if docstrings is None:
                # Do not call autodoc-process-docstring on get_doc() returns None.
                pass
            else:
                if not docstrings:
                    # append at least a dummy docstring, so that the event
                    # autodoc-process-docstring is fired and can add some
                    # content if desired
                    docstrings.append([])
                for i, line in enumerate(self.process_doc(docstrings)):
                    self.add_line(line, sourcename, i)

        # add additional content (e.g. from document), if present
        if more_content:
            for line, src in zip(more_content.data, more_content.items):
                self.add_line(line, src[0], src[1])

    def get_object_members(self, want_all: bool) -> Tuple[bool, ObjectMembers]:
        """Return `(members_check_module, members)` where `members` is a
        list of `(membername, member)` pairs of the members of *self.object*.

        If *want_all* is True, return all members.  Else, only return those
        members given by *self.options.members* (which may also be none).
        """
        warnings.warn('The implementation of Documenter.get_object_members() will be '
                      'removed from Sphinx-6.0.', RemovedInSphinx60Warning)
        members = get_object_members(self.object, self.objpath, self.get_attr, self.analyzer)
        if not want_all:
            if not self.options.members:
                return False, []  # type: ignore
            # specific members given
            selected = []
            for name in self.options.members:  # type: str
                if name in members:
                    selected.append((name, members[name].value))
                else:
                    logger.warning(__('missing attribute %s in object %s') %
                                   (name, self.fullname), type='autodoc')
            return False, selected
        elif self.options.inherited_members:
            return False, [(m.name, m.value) for m in members.values()]
        else:
            return False, [(m.name, m.value) for m in members.values()
                           if m.directly_defined]

    def filter_members(self, members: ObjectMembers, want_all: bool
                       ) -> List[Tuple[str, Any, bool]]:
        """Filter the given member list.

        Members are skipped if

        - they are private (except if given explicitly or the private-members
          option is set)
        - they are special methods (except if given explicitly or the
          special-members option is set)
        - they are undocumented (except if the undoc-members option is set)

        The user can override the skipping decision by connecting to the
        ``autodoc-skip-member`` event.
        """
        def is_filtered_inherited_member(name: str, obj: Any) -> bool:
            if inspect.isclass(self.object):
                for cls in self.object.__mro__:
                    if cls.__name__ == self.options.inherited_members and cls != self.object:
                        # given member is a member of specified *super class*
                        return True
                    elif name in cls.__dict__:
                        return False
                    elif name in self.get_attr(cls, '__annotations__', {}):
                        return False
                    elif isinstance(obj, ObjectMember) and obj.class_ is cls:
                        return False

            return False

        ret = []

        # search for members in source code too
        namespace = '.'.join(self.objpath)  # will be empty for modules

        if self.analyzer:
            attr_docs = self.analyzer.find_attr_docs()
        else:
            attr_docs = {}

        # process members and determine which to skip
        for obj in members:
            membername, member = obj
            # if isattr is True, the member is documented as an attribute
            if member is INSTANCEATTR:
                isattr = True
            elif (namespace, membername) in attr_docs:
                isattr = True
            else:
                isattr = False

            doc = getdoc(member, self.get_attr, self.config.autodoc_inherit_docstrings,
                         self.parent, self.object_name)
            if not isinstance(doc, str):
                # Ignore non-string __doc__
                doc = None

            # if the member __doc__ is the same as self's __doc__, it's just
            # inherited and therefore not the member's doc
            cls = self.get_attr(member, '__class__', None)
            if cls:
                cls_doc = self.get_attr(cls, '__doc__', None)
                if cls_doc == doc:
                    doc = None

            if isinstance(obj, ObjectMember) and obj.docstring:
                # hack for ClassDocumenter to inject docstring via ObjectMember
                doc = obj.docstring

            doc, metadata = separate_metadata(doc)
            has_doc = bool(doc)

            if 'private' in metadata:
                # consider a member private if docstring has "private" metadata
                isprivate = True
            elif 'public' in metadata:
                # consider a member public if docstring has "public" metadata
                isprivate = False
            else:
                isprivate = membername.startswith('_')

            keep = False
            if ismock(member):
                # mocked module or object
                pass
            elif self.options.exclude_members and membername in self.options.exclude_members:
                # remove members given by exclude-members
                keep = False
            elif want_all and special_member_re.match(membername):
                # special __methods__
                if self.options.special_members and membername in self.options.special_members:
                    if membername == '__doc__':
                        keep = False
                    elif is_filtered_inherited_member(membername, obj):
                        keep = False
                    else:
                        keep = has_doc or self.options.undoc_members
                else:
                    keep = False
            elif (namespace, membername) in attr_docs:
                if want_all and isprivate:
                    if self.options.private_members is None:
                        keep = False
                    else:
                        keep = membername in self.options.private_members
                else:
                    # keep documented attributes
                    keep = True
            elif want_all and isprivate:
                if has_doc or self.options.undoc_members:
                    if self.options.private_members is None:
                        keep = False
                    elif is_filtered_inherited_member(membername, obj):
                        keep = False
                    else:
                        keep = membername in self.options.private_members
                else:
                    keep = False
            else:
                if (self.options.members is ALL and
                        is_filtered_inherited_member(membername, obj)):
                    keep = False
                else:
                    # ignore undocumented members if :undoc-members: is not given
                    keep = has_doc or self.options.undoc_members

            if isinstance(obj, ObjectMember) and obj.skipped:
                # forcedly skipped member (ex. a module attribute not defined in __all__)
                keep = False

            # give the user a chance to decide whether this member
            # should be skipped
            if self.env.app:
                # let extensions preprocess docstrings
                try:
                    skip_user = self.env.app.emit_firstresult(
                        'autodoc-skip-member', self.objtype, membername, member,
                        not keep, self.options)
                    if skip_user is not None:
                        keep = not skip_user
                except Exception as exc:
                    logger.warning(__('autodoc: failed to determine %r to be documented, '
                                      'the following exception was raised:\n%s'),
                                   member, exc, type='autodoc')
                    keep = False

            if keep:
                ret.append((membername, member, isattr))

        return ret

    def document_members(self, all_members: bool = False) -> None:
        """Generate reST for member documentation.

        If *all_members* is True, do all members, else those given by
        *self.options.members*.
        """
        # set current namespace for finding members
        self.env.temp_data['autodoc:module'] = self.modname
        if self.objpath:
            self.env.temp_data['autodoc:class'] = self.objpath[0]

        want_all = (all_members or
                    self.options.inherited_members or
                    self.options.members is ALL)
        # find out which members are documentable
        members_check_module, members = self.get_object_members(want_all)

        # document non-skipped members
        memberdocumenters: List[Tuple[Documenter, bool]] = []
        for (mname, member, isattr) in self.filter_members(members, want_all):
            classes = [cls for cls in self.documenters.values()
                       if cls.can_document_member(member, mname, isattr, self)]
            if not classes:
                # don't know how to document this member
                continue
            # prefer the documenter with the highest priority
            classes.sort(key=lambda cls: cls.priority)
            # give explicitly separated module name, so that members
            # of inner classes can be documented
            full_mname = self.modname + '::' + '.'.join(self.objpath + [mname])
            documenter = classes[-1](self.directive, full_mname, self.indent)
            memberdocumenters.append((documenter, isattr))

        member_order = self.options.member_order or self.config.autodoc_member_order
        memberdocumenters = self.sort_members(memberdocumenters, member_order)

        for documenter, isattr in memberdocumenters:
            documenter.generate(
                all_members=True, real_modname=self.real_modname,
                check_module=members_check_module and not isattr)

        # reset current objects
        self.env.temp_data['autodoc:module'] = None
        self.env.temp_data['autodoc:class'] = None

    def sort_members(self, documenters: List[Tuple["Documenter", bool]],
                     order: str) -> List[Tuple["Documenter", bool]]:
        """Sort the given member list."""
        if order == 'groupwise':
            # sort by group; alphabetically within groups
            documenters.sort(key=lambda e: (e[0].member_order, e[0].name))
        elif order == 'bysource':
            if self.analyzer:
                # sort by source order, by virtue of the module analyzer
                tagorder = self.analyzer.tagorder

                def keyfunc(entry: Tuple[Documenter, bool]) -> int:
                    fullname = entry[0].name.split('::')[1]
                    return tagorder.get(fullname, len(tagorder))
                documenters.sort(key=keyfunc)
            else:
                # Assume that member discovery order matches source order.
                # This is a reasonable assumption in Python 3.6 and up, where
                # module.__dict__ is insertion-ordered.
                pass
        else:  # alphabetical
            documenters.sort(key=lambda e: e[0].name)

        return documenters

    def generate(self, more_content: Optional[StringList] = None, real_modname: str = None,
                 check_module: bool = False, all_members: bool = False) -> None:
        """Generate reST for the object given by *self.name*, and possibly for
        its members.

        If *more_content* is given, include that content. If *real_modname* is
        given, use that module name to find attribute docs. If *check_module* is
        True, only generate if the object is defined in the module name it is
        imported from. If *all_members* is True, document all members.
        """
        if not self.parse_name():
            # need a module to import
            logger.warning(
                __('don\'t know which module to import for autodocumenting '
                   '%r (try placing a "module" or "currentmodule" directive '
                   'in the document, or giving an explicit module name)') %
                self.name, type='autodoc')
            return

        # now, import the module and get object to document
        if not self.import_object():
            return

        # If there is no real module defined, figure out which to use.
        # The real module is used in the module analyzer to look up the module
        # where the attribute documentation would actually be found in.
        # This is used for situations where you have a module that collects the
        # functions and classes of internal submodules.
        guess_modname = self.get_real_modname()
        self.real_modname: str = real_modname or guess_modname

        # try to also get a source code analyzer for attribute docs
        try:
            self.analyzer = ModuleAnalyzer.for_module(self.real_modname)
            # parse right now, to get PycodeErrors on parsing (results will
            # be cached anyway)
            self.analyzer.find_attr_docs()
        except PycodeError as exc:
            logger.debug('[autodoc] module analyzer failed: %s', exc)
            # no source file -- e.g. for builtin and C modules
            self.analyzer = None
            # at least add the module.__file__ as a dependency
            if hasattr(self.module, '__file__') and self.module.__file__:
                self.directive.record_dependencies.add(self.module.__file__)
        else:
            self.directive.record_dependencies.add(self.analyzer.srcname)

        if self.real_modname != guess_modname:
            # Add module to dependency list if target object is defined in other module.
            try:
                analyzer = ModuleAnalyzer.for_module(guess_modname)
                self.directive.record_dependencies.add(analyzer.srcname)
            except PycodeError:
                pass

        # check __module__ of object (for members not given explicitly)
        if check_module:
            if not self.check_module():
                return

        sourcename = self.get_sourcename()

        # make sure that the result starts with an empty line.  This is
        # necessary for some situations where another directive preprocesses
        # reST and no starting newline is present
        self.add_line('', sourcename)

        # format the object's signature, if any
        try:
            sig = self.format_signature()
        except Exception as exc:
            logger.warning(__('error while formatting signature for %s: %s'),
                           self.fullname, exc, type='autodoc')
            return

        # generate the directive header and options, if applicable
        self.add_directive_header(sig)
        self.add_line('', sourcename)

        # e.g. the module directive doesn't have content
        self.indent += self.content_indent

        # add all content (from docstrings, attribute docs etc.)
        self.add_content(more_content)

        # document members, if possible
        self.document_members(all_members)


class ModuleDocumenter(Documenter):
    """
    Specialized Documenter subclass for modules.
    """
    objtype = 'module'
    content_indent = ''
    titles_allowed = True

    option_spec: OptionSpec = {
        'members': members_option, 'undoc-members': bool_option,
        'noindex': bool_option, 'inherited-members': inherited_members_option,
        'show-inheritance': bool_option, 'synopsis': identity,
        'platform': identity, 'deprecated': bool_option,
        'member-order': member_order_option, 'exclude-members': exclude_members_option,
        'private-members': members_option, 'special-members': members_option,
        'imported-members': bool_option, 'ignore-module-all': bool_option
    }

    def __init__(self, *args: Any) -> None:
        super().__init__(*args)
        merge_members_option(self.options)
        self.__all__: Optional[Sequence[str]] = None

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        # don't document submodules automatically
        return False

    def resolve_name(self, modname: str, parents: Any, path: str, base: Any
                     ) -> Tuple[str, List[str]]:
        if modname is not None:
            logger.warning(__('"::" in automodule name doesn\'t make sense'),
                           type='autodoc')
        return (path or '') + base, []

    def parse_name(self) -> bool:
        ret = super().parse_name()
        if self.args or self.retann:
            logger.warning(__('signature arguments or return annotation '
                              'given for automodule %s') % self.fullname,
                           type='autodoc')
        return ret

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)

        try:
            if not self.options.ignore_module_all:
                self.__all__ = inspect.getall(self.object)
        except ValueError as exc:
            # invalid __all__ found.
            logger.warning(__('__all__ should be a list of strings, not %r '
                              '(in module %s) -- ignoring __all__') %
                           (exc.args[0], self.fullname), type='autodoc')

        return ret

    def add_directive_header(self, sig: str) -> None:
        Documenter.add_directive_header(self, sig)

        sourcename = self.get_sourcename()

        # add some module-specific options
        if self.options.synopsis:
            self.add_line('   :synopsis: ' + self.options.synopsis, sourcename)
        if self.options.platform:
            self.add_line('   :platform: ' + self.options.platform, sourcename)
        if self.options.deprecated:
            self.add_line('   :deprecated:', sourcename)

    def get_module_members(self) -> Dict[str, ObjectMember]:
        """Get members of target module."""
        if self.analyzer:
            attr_docs = self.analyzer.attr_docs
        else:
            attr_docs = {}

        members: Dict[str, ObjectMember] = {}
        for name in dir(self.object):
            try:
                value = safe_getattr(self.object, name, None)
                if ismock(value):
                    value = undecorate(value)
                docstring = attr_docs.get(('', name), [])
                members[name] = ObjectMember(name, value, docstring="\n".join(docstring))
            except AttributeError:
                continue

        # annotation only member (ex. attr: int)
        for name in inspect.getannotations(self.object):
            if name not in members:
                docstring = attr_docs.get(('', name), [])
                members[name] = ObjectMember(name, INSTANCEATTR,
                                             docstring="\n".join(docstring))

        return members

    def get_object_members(self, want_all: bool) -> Tuple[bool, ObjectMembers]:
        members = self.get_module_members()
        if want_all:
            if self.__all__ is None:
                # for implicit module members, check __module__ to avoid
                # documenting imported objects
                return True, list(members.values())
            else:
                for member in members.values():
                    if member.__name__ not in self.__all__:
                        member.skipped = True

                return False, list(members.values())
        else:
            memberlist = self.options.members or []
            ret = []
            for name in memberlist:
                if name in members:
                    ret.append(members[name])
                else:
                    logger.warning(__('missing attribute mentioned in :members: option: '
                                      'module %s, attribute %s') %
                                   (safe_getattr(self.object, '__name__', '???'), name),
                                   type='autodoc')
            return False, ret

    def sort_members(self, documenters: List[Tuple["Documenter", bool]],
                     order: str) -> List[Tuple["Documenter", bool]]:
        if order == 'bysource' and self.__all__:
            # Sort alphabetically first (for members not listed on the __all__)
            documenters.sort(key=lambda e: e[0].name)

            # Sort by __all__
            def keyfunc(entry: Tuple[Documenter, bool]) -> int:
                name = entry[0].name.split('::')[1]
                if self.__all__ and name in self.__all__:
                    return self.__all__.index(name)
                else:
                    return len(self.__all__)
            documenters.sort(key=keyfunc)

            return documenters
        else:
            return super().sort_members(documenters, order)


class ModuleLevelDocumenter(Documenter):
    """
    Specialized Documenter subclass for objects on module level (functions,
    classes, data/constants).
    """
    def resolve_name(self, modname: str, parents: Any, path: str, base: Any
                     ) -> Tuple[str, List[str]]:
        if modname is None:
            if path:
                modname = path.rstrip('.')
            else:
                # if documenting a toplevel object without explicit module,
                # it can be contained in another auto directive ...
                modname = self.env.temp_data.get('autodoc:module')
                # ... or in the scope of a module directive
                if not modname:
                    modname = self.env.ref_context.get('py:module')
                # ... else, it stays None, which means invalid
        return modname, parents + [base]


class ClassLevelDocumenter(Documenter):
    """
    Specialized Documenter subclass for objects on class level (methods,
    attributes).
    """
    def resolve_name(self, modname: str, parents: Any, path: str, base: Any
                     ) -> Tuple[str, List[str]]:
        if modname is None:
            if path:
                mod_cls = path.rstrip('.')
            else:
                mod_cls = None
                # if documenting a class-level object without path,
                # there must be a current class, either from a parent
                # auto directive ...
                mod_cls = self.env.temp_data.get('autodoc:class')
                # ... or from a class directive
                if mod_cls is None:
                    mod_cls = self.env.ref_context.get('py:class')
                # ... if still None, there's no way to know
                if mod_cls is None:
                    return None, []
            modname, sep, cls = mod_cls.rpartition('.')
            parents = [cls]
            # if the module name is still missing, get it like above
            if not modname:
                modname = self.env.temp_data.get('autodoc:module')
            if not modname:
                modname = self.env.ref_context.get('py:module')
            # ... else, it stays None, which means invalid
        return modname, parents + [base]


class DocstringSignatureMixin:
    """
    Mixin for FunctionDocumenter and MethodDocumenter to provide the
    feature of reading the signature from the docstring.
    """
    _new_docstrings: List[List[str]] = None
    _signatures: List[str] = None

    def _find_signature(self) -> Tuple[str, str]:
        # candidates of the object name
        valid_names = [self.objpath[-1]]  # type: ignore
        if isinstance(self, ClassDocumenter):
            valid_names.append('__init__')
            if hasattr(self.object, '__mro__'):
                valid_names.extend(cls.__name__ for cls in self.object.__mro__)

        docstrings = self.get_doc()
        if docstrings is None:
            return None, None
        self._new_docstrings = docstrings[:]
        self._signatures = []
        result = None
        for i, doclines in enumerate(docstrings):
            for j, line in enumerate(doclines):
                if not line:
                    # no lines in docstring, no match
                    break

                if line.endswith('\\'):
                    line = line.rstrip('\\').rstrip()

                # match first line of docstring against signature RE
                match = py_ext_sig_re.match(line)
                if not match:
                    break
                exmod, path, base, args, retann = match.groups()

                # the base name must match ours
                if base not in valid_names:
                    break

                # re-prepare docstring to ignore more leading indentation
                tab_width = self.directive.state.document.settings.tab_width  # type: ignore
                self._new_docstrings[i] = prepare_docstring('\n'.join(doclines[j + 1:]),
                                                            tabsize=tab_width)

                if result is None:
                    # first signature
                    result = args, retann
                else:
                    # subsequent signatures
                    self._signatures.append("(%s) -> %s" % (args, retann))

            if result:
                # finish the loop when signature found
                break

        return result

    def get_doc(self, ignore: int = None) -> List[List[str]]:
        if self._new_docstrings is not None:
            return self._new_docstrings
        return super().get_doc(ignore)  # type: ignore

    def format_signature(self, **kwargs: Any) -> str:
        if self.args is None and self.config.autodoc_docstring_signature:  # type: ignore
            # only act if a signature is not explicitly given already, and if
            # the feature is enabled
            result = self._find_signature()
            if result is not None:
                self.args, self.retann = result
        sig = super().format_signature(**kwargs)  # type: ignore
        if self._signatures:
            return "\n".join([sig] + self._signatures)
        else:
            return sig


class DocstringStripSignatureMixin(DocstringSignatureMixin):
    """
    Mixin for AttributeDocumenter to provide the
    feature of stripping any function signature from the docstring.
    """
    def format_signature(self, **kwargs: Any) -> str:
        if self.args is None and self.config.autodoc_docstring_signature:  # type: ignore
            # only act if a signature is not explicitly given already, and if
            # the feature is enabled
            result = self._find_signature()
            if result is not None:
                # Discarding _args is a only difference with
                # DocstringSignatureMixin.format_signature.
                # Documenter.format_signature use self.args value to format.
                _args, self.retann = result
        return super().format_signature(**kwargs)


class FunctionDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # type: ignore
    """
    Specialized Documenter subclass for functions.
    """
    objtype = 'function'
    member_order = 30

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        # supports functions, builtins and bound methods exported at the module level
        return (inspect.isfunction(member) or inspect.isbuiltin(member) or
                (inspect.isroutine(member) and isinstance(parent, ModuleDocumenter)))

    def format_args(self, **kwargs: Any) -> str:
        if self.config.autodoc_typehints in ('none', 'description'):
            kwargs.setdefault('show_annotation', False)

        try:
            self.env.app.emit('autodoc-before-process-signature', self.object, False)
            sig = inspect.signature(self.object, type_aliases=self.config.autodoc_type_aliases)
            args = stringify_signature(sig, **kwargs)
        except TypeError as exc:
            logger.warning(__("Failed to get a function signature for %s: %s"),
                           self.fullname, exc)
            return None
        except ValueError:
            args = ''

        if self.config.strip_signature_backslash:
            # escape backslashes for reST
            args = args.replace('\\', '\\\\')
        return args

    def document_members(self, all_members: bool = False) -> None:
        pass

    def add_directive_header(self, sig: str) -> None:
        sourcename = self.get_sourcename()
        super().add_directive_header(sig)

        if inspect.iscoroutinefunction(self.object):
            self.add_line('   :async:', sourcename)

    def format_signature(self, **kwargs: Any) -> str:
        sigs = []
        if (self.analyzer and
                '.'.join(self.objpath) in self.analyzer.overloads and
                self.config.autodoc_typehints != 'none'):
            # Use signatures for overloaded functions instead of the implementation function.
            overloaded = True
        else:
            overloaded = False
            sig = super().format_signature(**kwargs)
            sigs.append(sig)

        if inspect.is_singledispatch_function(self.object):
            # append signature of singledispatch'ed functions
            for typ, func in self.object.registry.items():
                if typ is object:
                    pass  # default implementation. skipped.
                else:
                    dispatchfunc = self.annotate_to_first_argument(func, typ)
                    if dispatchfunc:
                        documenter = FunctionDocumenter(self.directive, '')
                        documenter.object = dispatchfunc
                        documenter.objpath = [None]
                        sigs.append(documenter.format_signature())
        if overloaded:
            actual = inspect.signature(self.object,
                                       type_aliases=self.config.autodoc_type_aliases)
            __globals__ = safe_getattr(self.object, '__globals__', {})
            for overload in self.analyzer.overloads.get('.'.join(self.objpath)):
                overload = self.merge_default_value(actual, overload)
                overload = evaluate_signature(overload, __globals__,
                                              self.config.autodoc_type_aliases)

                sig = stringify_signature(overload, **kwargs)
                sigs.append(sig)

        return "\n".join(sigs)

    def merge_default_value(self, actual: Signature, overload: Signature) -> Signature:
        """Merge default values of actual implementation to the overload variants."""
        parameters = list(overload.parameters.values())
        for i, param in enumerate(parameters):
            actual_param = actual.parameters.get(param.name)
            if actual_param and param.default == '...':
                parameters[i] = param.replace(default=actual_param.default)

        return overload.replace(parameters=parameters)

    def annotate_to_first_argument(self, func: Callable, typ: Type) -> Optional[Callable]:
        """Annotate type hint to the first argument of function if needed."""
        try:
            sig = inspect.signature(func, type_aliases=self.config.autodoc_type_aliases)
        except TypeError as exc:
            logger.warning(__("Failed to get a function signature for %s: %s"),
                           self.fullname, exc)
            return None
        except ValueError:
            return None

        if len(sig.parameters) == 0:
            return None

        def dummy():
            pass

        params = list(sig.parameters.values())
        if params[0].annotation is Parameter.empty:
            params[0] = params[0].replace(annotation=typ)
            try:
                dummy.__signature__ = sig.replace(parameters=params)  # type: ignore
                return dummy
            except (AttributeError, TypeError):
                # failed to update signature (ex. built-in or extension types)
                return None
        else:
            return None


class DecoratorDocumenter(FunctionDocumenter):
    """
    Specialized Documenter subclass for decorator functions.
    """
    objtype = 'decorator'

    # must be lower than FunctionDocumenter
    priority = -1

    def format_args(self, **kwargs: Any) -> Any:
        args = super().format_args(**kwargs)
        if ',' in args:
            return args
        else:
            return None


# Types which have confusing metaclass signatures it would be best not to show.
# These are listed by name, rather than storing the objects themselves, to avoid
# needing to import the modules.
_METACLASS_CALL_BLACKLIST = [
    'enum.EnumMeta.__call__',
]


# Types whose __new__ signature is a pass-thru.
_CLASS_NEW_BLACKLIST = [
    'typing.Generic.__new__',
]


class ClassDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # type: ignore
    """
    Specialized Documenter subclass for classes.
    """
    objtype = 'class'
    member_order = 20
    option_spec: OptionSpec = {
        'members': members_option, 'undoc-members': bool_option,
        'noindex': bool_option, 'inherited-members': inherited_members_option,
        'show-inheritance': bool_option, 'member-order': member_order_option,
        'exclude-members': exclude_members_option,
        'private-members': members_option, 'special-members': members_option,
        'class-doc-from': class_doc_from_option,
    }

    _signature_class: Any = None
    _signature_method_name: str = None

    def __init__(self, *args: Any) -> None:
        super().__init__(*args)

        if self.config.autodoc_class_signature == 'separated':
            self.options = self.options.copy()

            # show __init__() method
            if self.options.special_members is None:
                self.options['special-members'] = ['__new__', '__init__']
            else:
                self.options.special_members.append('__new__')
                self.options.special_members.append('__init__')

        merge_members_option(self.options)

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return isinstance(member, type)

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)
        # if the class is documented under another name, document it
        # as data/attribute
        if ret:
            if hasattr(self.object, '__name__'):
                self.doc_as_attr = (self.objpath[-1] != self.object.__name__)
            else:
                self.doc_as_attr = True
        return ret

    def _get_signature(self) -> Tuple[Optional[Any], Optional[str], Optional[Signature]]:
        def get_user_defined_function_or_method(obj: Any, attr: str) -> Any:
            """ Get the `attr` function or method from `obj`, if it is user-defined. """
            if inspect.is_builtin_class_method(obj, attr):
                return None
            attr = self.get_attr(obj, attr, None)
            if not (inspect.ismethod(attr) or inspect.isfunction(attr)):
                return None
            return attr

        # This sequence is copied from inspect._signature_from_callable.
        # ValueError means that no signature could be found, so we keep going.

        # First, we check the obj has a __signature__ attribute
        if (hasattr(self.object, '__signature__') and
                isinstance(self.object.__signature__, Signature)):
            return None, None, self.object.__signature__

        # Next, let's see if it has an overloaded __call__ defined
        # in its metaclass
        call = get_user_defined_function_or_method(type(self.object), '__call__')

        if call is not None:
            if "{0.__module__}.{0.__qualname__}".format(call) in _METACLASS_CALL_BLACKLIST:
                call = None

        if call is not None:
            self.env.app.emit('autodoc-before-process-signature', call, True)
            try:
                sig = inspect.signature(call, bound_method=True,
                                        type_aliases=self.config.autodoc_type_aliases)
                return type(self.object), '__call__', sig
            except ValueError:
                pass

        # Now we check if the 'obj' class has a '__new__' method
        new = get_user_defined_function_or_method(self.object, '__new__')

        if new is not None:
            if "{0.__module__}.{0.__qualname__}".format(new) in _CLASS_NEW_BLACKLIST:
                new = None

        if new is not None:
            self.env.app.emit('autodoc-before-process-signature', new, True)
            try:
                sig = inspect.signature(new, bound_method=True,
                                        type_aliases=self.config.autodoc_type_aliases)
                return self.object, '__new__', sig
            except ValueError:
                pass

        # Finally, we should have at least __init__ implemented
        init = get_user_defined_function_or_method(self.object, '__init__')
        if init is not None:
            self.env.app.emit('autodoc-before-process-signature', init, True)
            try:
                sig = inspect.signature(init, bound_method=True,
                                        type_aliases=self.config.autodoc_type_aliases)
                return self.object, '__init__', sig
            except ValueError:
                pass

        # None of the attributes are user-defined, so fall back to let inspect
        # handle it.
        # We don't know the exact method that inspect.signature will read
        # the signature from, so just pass the object itself to our hook.
        self.env.app.emit('autodoc-before-process-signature', self.object, False)
        try:
            sig = inspect.signature(self.object, bound_method=False,
                                    type_aliases=self.config.autodoc_type_aliases)
            return None, None, sig
        except ValueError:
            pass

        # Still no signature: happens e.g. for old-style classes
        # with __init__ in C and no `__text_signature__`.
        return None, None, None

    def format_args(self, **kwargs: Any) -> str:
        if self.config.autodoc_typehints in ('none', 'description'):
            kwargs.setdefault('show_annotation', False)

        try:
            self._signature_class, self._signature_method_name, sig = self._get_signature()
        except TypeError as exc:
            # __signature__ attribute contained junk
            logger.warning(__("Failed to get a constructor signature for %s: %s"),
                           self.fullname, exc)
            return None

        if sig is None:
            return None

        return stringify_signature(sig, show_return_annotation=False, **kwargs)

    def format_signature(self, **kwargs: Any) -> str:
        if self.doc_as_attr:
            return ''
        if self.config.autodoc_class_signature == 'separated':
            # do not show signatures
            return ''

        sig = super().format_signature()
        sigs = []

        overloads = self.get_overloaded_signatures()
        if overloads and self.config.autodoc_typehints != 'none':
            # Use signatures for overloaded methods instead of the implementation method.
            method = safe_getattr(self._signature_class, self._signature_method_name, None)
            __globals__ = safe_getattr(method, '__globals__', {})
            for overload in overloads:
                overload = evaluate_signature(overload, __globals__,
                                              self.config.autodoc_type_aliases)

                parameters = list(overload.parameters.values())
                overload = overload.replace(parameters=parameters[1:],
                                            return_annotation=Parameter.empty)
                sig = stringify_signature(overload, **kwargs)
                sigs.append(sig)
        else:
            sigs.append(sig)

        return "\n".join(sigs)

    def get_overloaded_signatures(self) -> List[Signature]:
        if self._signature_class and self._signature_method_name:
            for cls in self._signature_class.__mro__:
                try:
                    analyzer = ModuleAnalyzer.for_module(cls.__module__)
                    analyzer.analyze()
                    qualname = '.'.join([cls.__qualname__, self._signature_method_name])
                    if qualname in analyzer.overloads:
                        return analyzer.overloads.get(qualname)
                    elif qualname in analyzer.tagorder:
                        # the constructor is defined in the class, but not overrided.
                        return []
                except PycodeError:
                    pass

        return []

    def get_canonical_fullname(self) -> Optional[str]:
        __modname__ = safe_getattr(self.object, '__module__', self.modname)
        __qualname__ = safe_getattr(self.object, '__qualname__', None)
        if __qualname__ is None:
            __qualname__ = safe_getattr(self.object, '__name__', None)
        if __qualname__ and '<locals>' in __qualname__:
            # No valid qualname found if the object is defined as locals
            __qualname__ = None

        if __modname__ and __qualname__:
            return '.'.join([__modname__, __qualname__])
        else:
            return None

    def add_directive_header(self, sig: str) -> None:
        sourcename = self.get_sourcename()

        if self.doc_as_attr:
            self.directivetype = 'attribute'
        super().add_directive_header(sig)

        if self.analyzer and '.'.join(self.objpath) in self.analyzer.finals:
            self.add_line('   :final:', sourcename)

        canonical_fullname = self.get_canonical_fullname()
        if not self.doc_as_attr and canonical_fullname and self.fullname != canonical_fullname:
            self.add_line('   :canonical: %s' % canonical_fullname, sourcename)

        # add inheritance info, if wanted
        if not self.doc_as_attr and self.options.show_inheritance:
            if hasattr(self.object, '__orig_bases__') and len(self.object.__orig_bases__):
                # A subclass of generic types
                # refs: PEP-560 <https://www.python.org/dev/peps/pep-0560/>
                bases = list(self.object.__orig_bases__)
            elif hasattr(self.object, '__bases__') and len(self.object.__bases__):
                # A normal class
                bases = list(self.object.__bases__)
            else:
                bases = []

            self.env.events.emit('autodoc-process-bases',
                                 self.fullname, self.object, self.options, bases)

            base_classes = [restify(cls) for cls in bases]
            sourcename = self.get_sourcename()
            self.add_line('', sourcename)
            self.add_line('   ' + _('Bases: %s') % ', '.join(base_classes), sourcename)

    def get_object_members(self, want_all: bool) -> Tuple[bool, ObjectMembers]:
        members = get_class_members(self.object, self.objpath, self.get_attr)
        if not want_all:
            if not self.options.members:
                return False, []  # type: ignore
            # specific members given
            selected = []
            for name in self.options.members:  # type: str
                if name in members:
                    selected.append(members[name])
                else:
                    logger.warning(__('missing attribute %s in object %s') %
                                   (name, self.fullname), type='autodoc')
            return False, selected
        elif self.options.inherited_members:
            return False, list(members.values())
        else:
            return False, [m for m in members.values() if m.class_ == self.object]

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if self.doc_as_attr:
            # Don't show the docstring of the class when it is an alias.
            comment = self.get_variable_comment()
            if comment:
                return []
            else:
                return None

        lines = getattr(self, '_new_docstrings', None)
        if lines is not None:
            return lines

        classdoc_from = self.options.get('class-doc-from', self.config.autoclass_content)

        docstrings = []
        attrdocstring = self.get_attr(self.object, '__doc__', None)
        if attrdocstring:
            docstrings.append(attrdocstring)

        # for classes, what the "docstring" is can be controlled via a
        # config value; the default is only the class docstring
        if classdoc_from in ('both', 'init'):
            __init__ = self.get_attr(self.object, '__init__', None)
            initdocstring = getdoc(__init__, self.get_attr,
                                   self.config.autodoc_inherit_docstrings,
                                   self.object, '__init__')
            # for new-style classes, no __init__ means default __init__
            if (initdocstring is not None and
                (initdocstring == object.__init__.__doc__ or  # for pypy
                 initdocstring.strip() == object.__init__.__doc__)):  # for !pypy
                initdocstring = None
            if not initdocstring:
                # try __new__
                __new__ = self.get_attr(self.object, '__new__', None)
                initdocstring = getdoc(__new__, self.get_attr,
                                       self.config.autodoc_inherit_docstrings,
                                       self.object, '__new__')
                # for new-style classes, no __new__ means default __new__
                if (initdocstring is not None and
                    (initdocstring == object.__new__.__doc__ or  # for pypy
                     initdocstring.strip() == object.__new__.__doc__)):  # for !pypy
                    initdocstring = None
            if initdocstring:
                if classdoc_from == 'init':
                    docstrings = [initdocstring]
                else:
                    docstrings.append(initdocstring)

        tab_width = self.directive.state.document.settings.tab_width
        return [prepare_docstring(docstring, ignore, tab_width) for docstring in docstrings]

    def get_variable_comment(self) -> Optional[List[str]]:
        try:
            key = ('', '.'.join(self.objpath))
            analyzer = ModuleAnalyzer.for_module(self.get_real_modname())
            analyzer.analyze()
            return list(self.analyzer.attr_docs.get(key, []))
        except PycodeError:
            return None

    def add_content(self, more_content: Optional[StringList], no_docstring: bool = False
                    ) -> None:
        if self.doc_as_attr and not self.get_variable_comment():
            try:
                more_content = StringList([_('alias of %s') % restify(self.object)], source='')
            except AttributeError:
                pass  # Invalid class object is passed.

        super().add_content(more_content)

    def document_members(self, all_members: bool = False) -> None:
        if self.doc_as_attr:
            return
        super().document_members(all_members)

    def generate(self, more_content: Optional[StringList] = None, real_modname: str = None,
                 check_module: bool = False, all_members: bool = False) -> None:
        # Do not pass real_modname and use the name from the __module__
        # attribute of the class.
        # If a class gets imported into the module real_modname
        # the analyzer won't find the source of the class, if
        # it looks in real_modname.
        return super().generate(more_content=more_content,
                                check_module=check_module,
                                all_members=all_members)


class ExceptionDocumenter(ClassDocumenter):
    """
    Specialized ClassDocumenter subclass for exceptions.
    """
    objtype = 'exception'
    member_order = 10

    # needs a higher priority than ClassDocumenter
    priority = 10

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return isinstance(member, type) and issubclass(member, BaseException)


class DataDocumenterMixinBase:
    # define types of instance variables
    config: Config = None
    env: BuildEnvironment = None
    modname: str = None
    parent: Any = None
    object: Any = None
    objpath: List[str] = None

    def should_suppress_directive_header(self) -> bool:
        """Check directive header should be suppressed."""
        return False

    def should_suppress_value_header(self) -> bool:
        """Check :value: header should be suppressed."""
        return False

    def update_content(self, more_content: StringList) -> None:
        """Update docstring for the NewType object."""
        pass


class GenericAliasMixin(DataDocumenterMixinBase):
    """
    Mixin for DataDocumenter and AttributeDocumenter to provide the feature for
    supporting GenericAliases.
    """

    def should_suppress_directive_header(self) -> bool:
        return (inspect.isgenericalias(self.object) or
                super().should_suppress_directive_header())

    def update_content(self, more_content: StringList) -> None:
        if inspect.isgenericalias(self.object):
            more_content.append(_('alias of %s') % restify(self.object), '')
            more_content.append('', '')

        super().update_content(more_content)


class NewTypeMixin(DataDocumenterMixinBase):
    """
    Mixin for DataDocumenter and AttributeDocumenter to provide the feature for
    supporting NewTypes.
    """

    def should_suppress_directive_header(self) -> bool:
        return (inspect.isNewType(self.object) or
                super().should_suppress_directive_header())

    def update_content(self, more_content: StringList) -> None:
        if inspect.isNewType(self.object):
            supertype = restify(self.object.__supertype__)
            more_content.append(_('alias of %s') % supertype, '')
            more_content.append('', '')

        super().update_content(more_content)


class TypeVarMixin(DataDocumenterMixinBase):
    """
    Mixin for DataDocumenter and AttributeDocumenter to provide the feature for
    supporting TypeVars.
    """

    def should_suppress_directive_header(self) -> bool:
        return (isinstance(self.object, TypeVar) or
                super().should_suppress_directive_header())

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if ignore is not None:
            warnings.warn("The 'ignore' argument to autodoc.%s.get_doc() is deprecated."
                          % self.__class__.__name__,
                          RemovedInSphinx50Warning, stacklevel=2)

        if isinstance(self.object, TypeVar):
            if self.object.__doc__ != TypeVar.__doc__:
                return super().get_doc()  # type: ignore
            else:
                return []
        else:
            return super().get_doc()  # type: ignore

    def update_content(self, more_content: StringList) -> None:
        if isinstance(self.object, TypeVar):
            attrs = [repr(self.object.__name__)]
            for constraint in self.object.__constraints__:
                attrs.append(stringify_typehint(constraint))
            if self.object.__bound__:
                attrs.append(r"bound=\ " + restify(self.object.__bound__))
            if self.object.__covariant__:
                attrs.append("covariant=True")
            if self.object.__contravariant__:
                attrs.append("contravariant=True")

            more_content.append(_('alias of TypeVar(%s)') % ", ".join(attrs), '')
            more_content.append('', '')

        super().update_content(more_content)


class UninitializedGlobalVariableMixin(DataDocumenterMixinBase):
    """
    Mixin for DataDocumenter to provide the feature for supporting uninitialized
    (type annotation only) global variables.
    """

    def import_object(self, raiseerror: bool = False) -> bool:
        try:
            return super().import_object(raiseerror=True)  # type: ignore
        except ImportError as exc:
            # annotation only instance variable (PEP-526)
            try:
                with mock(self.config.autodoc_mock_imports):
                    parent = import_module(self.modname, self.config.autodoc_warningiserror)
                    annotations = get_type_hints(parent, None,
                                                 self.config.autodoc_type_aliases)
                    if self.objpath[-1] in annotations:
                        self.object = UNINITIALIZED_ATTR
                        self.parent = parent
                        return True
            except ImportError:
                pass

            if raiseerror:
                raise
            else:
                logger.warning(exc.args[0], type='autodoc', subtype='import_object')
                self.env.note_reread()
                return False

    def should_suppress_value_header(self) -> bool:
        return (self.object is UNINITIALIZED_ATTR or
                super().should_suppress_value_header())

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if self.object is UNINITIALIZED_ATTR:
            return []
        else:
            return super().get_doc(ignore)  # type: ignore


class DataDocumenter(GenericAliasMixin, NewTypeMixin, TypeVarMixin,
                     UninitializedGlobalVariableMixin, ModuleLevelDocumenter):
    """
    Specialized Documenter subclass for data items.
    """
    objtype = 'data'
    member_order = 40
    priority = -10
    option_spec: OptionSpec = dict(ModuleLevelDocumenter.option_spec)
    option_spec["annotation"] = annotation_option
    option_spec["no-value"] = bool_option

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return isinstance(parent, ModuleDocumenter) and isattr

    def update_annotations(self, parent: Any) -> None:
        """Update __annotations__ to support type_comment and so on."""
        annotations = dict(inspect.getannotations(parent))
        parent.__annotations__ = annotations

        try:
            analyzer = ModuleAnalyzer.for_module(self.modname)
            analyzer.analyze()
            for (classname, attrname), annotation in analyzer.annotations.items():
                if classname == '' and attrname not in annotations:
                    annotations[attrname] = annotation
        except PycodeError:
            pass

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)
        if self.parent:
            self.update_annotations(self.parent)

        return ret

    def should_suppress_value_header(self) -> bool:
        if super().should_suppress_value_header():
            return True
        else:
            doc = self.get_doc()
            docstring, metadata = separate_metadata('\n'.join(sum(doc, [])))
            if 'hide-value' in metadata:
                return True

        return False

    def add_directive_header(self, sig: str) -> None:
        super().add_directive_header(sig)
        sourcename = self.get_sourcename()
        if self.options.annotation is SUPPRESS or self.should_suppress_directive_header():
            pass
        elif self.options.annotation:
            self.add_line('   :annotation: %s' % self.options.annotation,
                          sourcename)
        else:
            if self.config.autodoc_typehints != 'none':
                # obtain annotation for this data
                annotations = get_type_hints(self.parent, None,
                                             self.config.autodoc_type_aliases)
                if self.objpath[-1] in annotations:
                    objrepr = stringify_typehint(annotations.get(self.objpath[-1]))
                    self.add_line('   :type: ' + objrepr, sourcename)

            try:
                if self.options.no_value or self.should_suppress_value_header():
                    pass
                else:
                    objrepr = object_description(self.object)
                    self.add_line('   :value: ' + objrepr, sourcename)
            except ValueError:
                pass

    def document_members(self, all_members: bool = False) -> None:
        pass

    def get_real_modname(self) -> str:
        real_modname = self.get_attr(self.parent or self.object, '__module__', None)
        return real_modname or self.modname

    def get_module_comment(self, attrname: str) -> Optional[List[str]]:
        try:
            analyzer = ModuleAnalyzer.for_module(self.modname)
            analyzer.analyze()
            key = ('', attrname)
            if key in analyzer.attr_docs:
                return list(analyzer.attr_docs[key])
        except PycodeError:
            pass

        return None

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        # Check the variable has a docstring-comment
        comment = self.get_module_comment(self.objpath[-1])
        if comment:
            return [comment]
        else:
            return super().get_doc(ignore)

    def add_content(self, more_content: Optional[StringList], no_docstring: bool = False
                    ) -> None:
        # Disable analyzing variable comment on Documenter.add_content() to control it on
        # DataDocumenter.add_content()
        self.analyzer = None

        if not more_content:
            more_content = StringList()

        self.update_content(more_content)
        super().add_content(more_content, no_docstring=no_docstring)


class NewTypeDataDocumenter(DataDocumenter):
    """
    Specialized Documenter subclass for NewTypes.

    Note: This must be invoked before FunctionDocumenter because NewType is a kind of
    function object.
    """

    objtype = 'newtypedata'
    directivetype = 'data'
    priority = FunctionDocumenter.priority + 1

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return inspect.isNewType(member) and isattr


class MethodDocumenter(DocstringSignatureMixin, ClassLevelDocumenter):  # type: ignore
    """
    Specialized Documenter subclass for methods (normal, static and class).
    """
    objtype = 'method'
    directivetype = 'method'
    member_order = 50
    priority = 1  # must be more than FunctionDocumenter

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return inspect.isroutine(member) and not isinstance(parent, ModuleDocumenter)

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)
        if not ret:
            return ret

        # to distinguish classmethod/staticmethod
        obj = self.parent.__dict__.get(self.object_name)
        if obj is None:
            obj = self.object

        if (inspect.isclassmethod(obj) or
                inspect.isstaticmethod(obj, cls=self.parent, name=self.object_name)):
            # document class and static members before ordinary ones
            self.member_order = self.member_order - 1

        return ret

    def format_args(self, **kwargs: Any) -> str:
        if self.config.autodoc_typehints in ('none', 'description'):
            kwargs.setdefault('show_annotation', False)

        try:
            if self.object == object.__init__ and self.parent != object:
                # Classes not having own __init__() method are shown as no arguments.
                #
                # Note: The signature of object.__init__() is (self, /, *args, **kwargs).
                #       But it makes users confused.
                args = '()'
            else:
                if inspect.isstaticmethod(self.object, cls=self.parent, name=self.object_name):
                    self.env.app.emit('autodoc-before-process-signature', self.object, False)
                    sig = inspect.signature(self.object, bound_method=False,
                                            type_aliases=self.config.autodoc_type_aliases)
                else:
                    self.env.app.emit('autodoc-before-process-signature', self.object, True)
                    sig = inspect.signature(self.object, bound_method=True,
                                            type_aliases=self.config.autodoc_type_aliases)
                args = stringify_signature(sig, **kwargs)
        except TypeError as exc:
            logger.warning(__("Failed to get a method signature for %s: %s"),
                           self.fullname, exc)
            return None
        except ValueError:
            args = ''

        if self.config.strip_signature_backslash:
            # escape backslashes for reST
            args = args.replace('\\', '\\\\')
        return args

    def add_directive_header(self, sig: str) -> None:
        super().add_directive_header(sig)

        sourcename = self.get_sourcename()
        obj = self.parent.__dict__.get(self.object_name, self.object)
        if inspect.isabstractmethod(obj):
            self.add_line('   :abstractmethod:', sourcename)
        if inspect.iscoroutinefunction(obj):
            self.add_line('   :async:', sourcename)
        if inspect.isclassmethod(obj):
            self.add_line('   :classmethod:', sourcename)
        if inspect.isstaticmethod(obj, cls=self.parent, name=self.object_name):
            self.add_line('   :staticmethod:', sourcename)
        if self.analyzer and '.'.join(self.objpath) in self.analyzer.finals:
            self.add_line('   :final:', sourcename)

    def document_members(self, all_members: bool = False) -> None:
        pass

    def format_signature(self, **kwargs: Any) -> str:
        sigs = []
        if (self.analyzer and
                '.'.join(self.objpath) in self.analyzer.overloads and
                self.config.autodoc_typehints != 'none'):
            # Use signatures for overloaded methods instead of the implementation method.
            overloaded = True
        else:
            overloaded = False
            sig = super().format_signature(**kwargs)
            sigs.append(sig)

        meth = self.parent.__dict__.get(self.objpath[-1])
        if inspect.is_singledispatch_method(meth):
            # append signature of singledispatch'ed functions
            for typ, func in meth.dispatcher.registry.items():
                if typ is object:
                    pass  # default implementation. skipped.
                else:
                    dispatchmeth = self.annotate_to_first_argument(func, typ)
                    if dispatchmeth:
                        documenter = MethodDocumenter(self.directive, '')
                        documenter.parent = self.parent
                        documenter.object = dispatchmeth
                        documenter.objpath = [None]
                        sigs.append(documenter.format_signature())
        if overloaded:
            if inspect.isstaticmethod(self.object, cls=self.parent, name=self.object_name):
                actual = inspect.signature(self.object, bound_method=False,
                                           type_aliases=self.config.autodoc_type_aliases)
            else:
                actual = inspect.signature(self.object, bound_method=True,
                                           type_aliases=self.config.autodoc_type_aliases)

            __globals__ = safe_getattr(self.object, '__globals__', {})
            for overload in self.analyzer.overloads.get('.'.join(self.objpath)):
                overload = self.merge_default_value(actual, overload)
                overload = evaluate_signature(overload, __globals__,
                                              self.config.autodoc_type_aliases)

                if not inspect.isstaticmethod(self.object, cls=self.parent,
                                              name=self.object_name):
                    parameters = list(overload.parameters.values())
                    overload = overload.replace(parameters=parameters[1:])
                sig = stringify_signature(overload, **kwargs)
                sigs.append(sig)

        return "\n".join(sigs)

    def merge_default_value(self, actual: Signature, overload: Signature) -> Signature:
        """Merge default values of actual implementation to the overload variants."""
        parameters = list(overload.parameters.values())
        for i, param in enumerate(parameters):
            actual_param = actual.parameters.get(param.name)
            if actual_param and param.default == '...':
                parameters[i] = param.replace(default=actual_param.default)

        return overload.replace(parameters=parameters)

    def annotate_to_first_argument(self, func: Callable, typ: Type) -> Optional[Callable]:
        """Annotate type hint to the first argument of function if needed."""
        try:
            sig = inspect.signature(func, type_aliases=self.config.autodoc_type_aliases)
        except TypeError as exc:
            logger.warning(__("Failed to get a method signature for %s: %s"),
                           self.fullname, exc)
            return None
        except ValueError:
            return None

        if len(sig.parameters) == 1:
            return None

        def dummy():
            pass

        params = list(sig.parameters.values())
        if params[1].annotation is Parameter.empty:
            params[1] = params[1].replace(annotation=typ)
            try:
                dummy.__signature__ = sig.replace(parameters=params)  # type: ignore
                return dummy
            except (AttributeError, TypeError):
                # failed to update signature (ex. built-in or extension types)
                return None
        else:
            return None

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if self.objpath[-1] == '__init__':
            docstring = getdoc(self.object, self.get_attr,
                               self.config.autodoc_inherit_docstrings,
                               self.parent, self.object_name)
            if (docstring is not None and
                (docstring == object.__init__.__doc__ or  # for pypy
                 docstring.strip() == object.__init__.__doc__)):  # for !pypy
                docstring = None
            if docstring:
                tab_width = self.directive.state.document.settings.tab_width
                return [prepare_docstring(docstring, tabsize=tab_width)]
            else:
                return []
        elif self.objpath[-1] == '__new__':
            __new__ = self.get_attr(self.object, '__new__', None)
            if __new__:
                docstring = getdoc(__new__, self.get_attr,
                                   self.config.autodoc_inherit_docstrings,
                                   self.parent, self.object_name)
                if (docstring is not None and
                    (docstring == object.__new__.__doc__ or  # for pypy
                     docstring.strip() == object.__new__.__doc__)):  # for !pypy
                    docstring = None
            if docstring:
                tab_width = self.directive.state.document.settings.tab_width
                return [prepare_docstring(docstring, tabsize=tab_width)]
            else:
                return []
        else:
            return super().get_doc()


class NonDataDescriptorMixin(DataDocumenterMixinBase):
    """
    Mixin for AttributeDocumenter to provide the feature for supporting non
    data-descriptors.

    .. note:: This mix-in must be inherited after other mix-ins.  Otherwise, docstring
              and :value: header will be suppressed unexpectedly.
    """

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)  # type: ignore
        if ret and not inspect.isattributedescriptor(self.object):
            self.non_data_descriptor = True
        else:
            self.non_data_descriptor = False

        return ret

    def should_suppress_value_header(self) -> bool:
        return (not getattr(self, 'non_data_descriptor', False) or
                super().should_suppress_directive_header())

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if getattr(self, 'non_data_descriptor', False):
            # the docstring of non datadescriptor is very probably the wrong thing
            # to display
            return None
        else:
            return super().get_doc(ignore)  # type: ignore


class SlotsMixin(DataDocumenterMixinBase):
    """
    Mixin for AttributeDocumenter to provide the feature for supporting __slots__.
    """

    def isslotsattribute(self) -> bool:
        """Check the subject is an attribute in __slots__."""
        try:
            __slots__ = inspect.getslots(self.parent)
            if __slots__ and self.objpath[-1] in __slots__:
                return True
            else:
                return False
        except (ValueError, TypeError):
            return False

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)  # type: ignore
        if self.isslotsattribute():
            self.object = SLOTSATTR

        return ret

    def should_suppress_directive_header(self) -> bool:
        if self.object is SLOTSATTR:
            self._datadescriptor = True
            return True
        else:
            return super().should_suppress_directive_header()

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if self.object is SLOTSATTR:
            try:
                __slots__ = inspect.getslots(self.parent)
                if __slots__ and __slots__.get(self.objpath[-1]):
                    docstring = prepare_docstring(__slots__[self.objpath[-1]])
                    return [docstring]
                else:
                    return []
            except ValueError as exc:
                logger.warning(__('Invalid __slots__ found on %s. Ignored.'),
                               (self.parent.__qualname__, exc), type='autodoc')
                return []
        else:
            return super().get_doc(ignore)  # type: ignore


class RuntimeInstanceAttributeMixin(DataDocumenterMixinBase):
    """
    Mixin for AttributeDocumenter to provide the feature for supporting runtime
    instance attributes (that are defined in __init__() methods with doc-comments).

    Example:

        class Foo:
            def __init__(self):
                self.attr = None  #: This is a target of this mix-in.
    """

    RUNTIME_INSTANCE_ATTRIBUTE = object()

    def is_runtime_instance_attribute(self, parent: Any) -> bool:
        """Check the subject is an attribute defined in __init__()."""
        # An instance variable defined in __init__().
        if self.get_attribute_comment(parent, self.objpath[-1]):  # type: ignore
            return True
        elif self.is_runtime_instance_attribute_not_commented(parent):
            return True
        else:
            return False

    def is_runtime_instance_attribute_not_commented(self, parent: Any) -> bool:
        """Check the subject is an attribute defined in __init__() without comment."""
        for cls in inspect.getmro(parent):
            try:
                module = safe_getattr(cls, '__module__')
                qualname = safe_getattr(cls, '__qualname__')

                analyzer = ModuleAnalyzer.for_module(module)
                analyzer.analyze()
                if qualname and self.objpath:
                    key = '.'.join([qualname, self.objpath[-1]])
                    if key in analyzer.tagorder:
                        return True
            except (AttributeError, PycodeError):
                pass

        return None

    def import_object(self, raiseerror: bool = False) -> bool:
        """Check the existence of runtime instance attribute when failed to import the
        attribute."""
        try:
            return super().import_object(raiseerror=True)  # type: ignore
        except ImportError as exc:
            try:
                with mock(self.config.autodoc_mock_imports):
                    ret = import_object(self.modname, self.objpath[:-1], 'class',
                                        attrgetter=self.get_attr,  # type: ignore
                                        warningiserror=self.config.autodoc_warningiserror)
                    parent = ret[3]
                    if self.is_runtime_instance_attribute(parent):
                        self.object = self.RUNTIME_INSTANCE_ATTRIBUTE
                        self.parent = parent
                        return True
            except ImportError:
                pass

            if raiseerror:
                raise
            else:
                logger.warning(exc.args[0], type='autodoc', subtype='import_object')
                self.env.note_reread()
                return False

    def should_suppress_value_header(self) -> bool:
        return (self.object is self.RUNTIME_INSTANCE_ATTRIBUTE or
                super().should_suppress_value_header())

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if (self.object is self.RUNTIME_INSTANCE_ATTRIBUTE and
                self.is_runtime_instance_attribute_not_commented(self.parent)):
            return None
        else:
            return super().get_doc(ignore)  # type: ignore


class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
    """
    Mixin for AttributeDocumenter to provide the feature for supporting uninitialized
    instance attributes (PEP-526 styled, annotation only attributes).

    Example:

        class Foo:
            attr: int  #: This is a target of this mix-in.
    """

    def is_uninitialized_instance_attribute(self, parent: Any) -> bool:
        """Check the subject is an annotation only attribute."""
        annotations = get_type_hints(parent, None, self.config.autodoc_type_aliases)
        if self.objpath[-1] in annotations:
            return True
        else:
            return False

    def import_object(self, raiseerror: bool = False) -> bool:
        """Check the exisitence of uninitialized instance attribute when failed to import
        the attribute."""
        try:
            return super().import_object(raiseerror=True)  # type: ignore
        except ImportError as exc:
            try:
                ret = import_object(self.modname, self.objpath[:-1], 'class',
                                    attrgetter=self.get_attr,  # type: ignore
                                    warningiserror=self.config.autodoc_warningiserror)
                parent = ret[3]
                if self.is_uninitialized_instance_attribute(parent):
                    self.object = UNINITIALIZED_ATTR
                    self.parent = parent
                    return True
            except ImportError:
                pass

            if raiseerror:
                raise
            else:
                logger.warning(exc.args[0], type='autodoc', subtype='import_object')
                self.env.note_reread()
                return False

    def should_suppress_value_header(self) -> bool:
        return (self.object is UNINITIALIZED_ATTR or
                super().should_suppress_value_header())

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        if self.object is UNINITIALIZED_ATTR:
            return None
        else:
            return super().get_doc(ignore)  # type: ignore


class AttributeDocumenter(GenericAliasMixin, NewTypeMixin, SlotsMixin,  # type: ignore
                          TypeVarMixin, RuntimeInstanceAttributeMixin,
                          UninitializedInstanceAttributeMixin, NonDataDescriptorMixin,
                          DocstringStripSignatureMixin, ClassLevelDocumenter):
    """
    Specialized Documenter subclass for attributes.
    """
    objtype = 'attribute'
    member_order = 60
    option_spec: OptionSpec = dict(ModuleLevelDocumenter.option_spec)
    option_spec["annotation"] = annotation_option
    option_spec["no-value"] = bool_option

    # must be higher than the MethodDocumenter, else it will recognize
    # some non-data descriptors as methods
    priority = 10

    @staticmethod
    def is_function_or_method(obj: Any) -> bool:
        return inspect.isfunction(obj) or inspect.isbuiltin(obj) or inspect.ismethod(obj)

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        if inspect.isattributedescriptor(member):
            return True
        elif (not isinstance(parent, ModuleDocumenter) and
              not inspect.isroutine(member) and
              not isinstance(member, type)):
            return True
        else:
            return False

    def document_members(self, all_members: bool = False) -> None:
        pass

    def isinstanceattribute(self) -> bool:
        """Check the subject is an instance attribute."""
        warnings.warn('AttributeDocumenter.isinstanceattribute() is deprecated.',
                      RemovedInSphinx50Warning)
        # uninitialized instance variable (PEP-526)
        with mock(self.config.autodoc_mock_imports):
            try:
                ret = import_object(self.modname, self.objpath[:-1], 'class',
                                    attrgetter=self.get_attr,
                                    warningiserror=self.config.autodoc_warningiserror)
                self.parent = ret[3]
                annotations = get_type_hints(self.parent, None,
                                             self.config.autodoc_type_aliases)
                if self.objpath[-1] in annotations:
                    self.object = UNINITIALIZED_ATTR
                    return True
            except ImportError:
                pass

        return False

    def update_annotations(self, parent: Any) -> None:
        """Update __annotations__ to support type_comment and so on."""
        try:
            annotations = dict(inspect.getannotations(parent))
            parent.__annotations__ = annotations

            for cls in inspect.getmro(parent):
                try:
                    module = safe_getattr(cls, '__module__')
                    qualname = safe_getattr(cls, '__qualname__')

                    analyzer = ModuleAnalyzer.for_module(module)
                    analyzer.analyze()
                    for (classname, attrname), annotation in analyzer.annotations.items():
                        if classname == qualname and attrname not in annotations:
                            annotations[attrname] = annotation
                except (AttributeError, PycodeError):
                    pass
        except (AttributeError, TypeError):
            # Failed to set __annotations__ (built-in, extensions, etc.)
            pass

    def import_object(self, raiseerror: bool = False) -> bool:
        ret = super().import_object(raiseerror)
        if inspect.isenumattribute(self.object):
            self.object = self.object.value
        if self.parent:
            self.update_annotations(self.parent)

        return ret

    def get_real_modname(self) -> str:
        real_modname = self.get_attr(self.parent or self.object, '__module__', None)
        return real_modname or self.modname

    def should_suppress_value_header(self) -> bool:
        if super().should_suppress_value_header():
            return True
        else:
            doc = self.get_doc()
            if doc:
                docstring, metadata = separate_metadata('\n'.join(sum(doc, [])))
                if 'hide-value' in metadata:
                    return True

        return False

    def add_directive_header(self, sig: str) -> None:
        super().add_directive_header(sig)
        sourcename = self.get_sourcename()
        if self.options.annotation is SUPPRESS or self.should_suppress_directive_header():
            pass
        elif self.options.annotation:
            self.add_line('   :annotation: %s' % self.options.annotation, sourcename)
        else:
            if self.config.autodoc_typehints != 'none':
                # obtain type annotation for this attribute
                annotations = get_type_hints(self.parent, None,
                                             self.config.autodoc_type_aliases)
                if self.objpath[-1] in annotations:
                    objrepr = stringify_typehint(annotations.get(self.objpath[-1]))
                    self.add_line('   :type: ' + objrepr, sourcename)

            try:
                if self.options.no_value or self.should_suppress_value_header():
                    pass
                else:
                    objrepr = object_description(self.object)
                    self.add_line('   :value: ' + objrepr, sourcename)
            except ValueError:
                pass

    def get_attribute_comment(self, parent: Any, attrname: str) -> Optional[List[str]]:
        for cls in inspect.getmro(parent):
            try:
                module = safe_getattr(cls, '__module__')
                qualname = safe_getattr(cls, '__qualname__')

                analyzer = ModuleAnalyzer.for_module(module)
                analyzer.analyze()
                if qualname and self.objpath:
                    key = (qualname, attrname)
                    if key in analyzer.attr_docs:
                        return list(analyzer.attr_docs[key])
            except (AttributeError, PycodeError):
                pass

        return None

    def get_doc(self, ignore: int = None) -> Optional[List[List[str]]]:
        # Check the attribute has a docstring-comment
        comment = self.get_attribute_comment(self.parent, self.objpath[-1])
        if comment:
            return [comment]

        try:
            # Disable `autodoc_inherit_docstring` temporarily to avoid to obtain
            # a docstring from the value which descriptor returns unexpectedly.
            # ref: https://github.com/sphinx-doc/sphinx/issues/7805
            orig = self.config.autodoc_inherit_docstrings
            self.config.autodoc_inherit_docstrings = False  # type: ignore
            return super().get_doc(ignore)
        finally:
            self.config.autodoc_inherit_docstrings = orig  # type: ignore

    def add_content(self, more_content: Optional[StringList], no_docstring: bool = False
                    ) -> None:
        # Disable analyzing attribute comment on Documenter.add_content() to control it on
        # AttributeDocumenter.add_content()
        self.analyzer = None

        if more_content is None:
            more_content = StringList()
        self.update_content(more_content)
        super().add_content(more_content, no_docstring)


class PropertyDocumenter(DocstringStripSignatureMixin, ClassLevelDocumenter):  # type: ignore
    """
    Specialized Documenter subclass for properties.
    """
    objtype = 'property'
    member_order = 60

    # before AttributeDocumenter
    priority = AttributeDocumenter.priority + 1

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return inspect.isproperty(member) and isinstance(parent, ClassDocumenter)

    def document_members(self, all_members: bool = False) -> None:
        pass

    def get_real_modname(self) -> str:
        real_modname = self.get_attr(self.parent or self.object, '__module__', None)
        return real_modname or self.modname

    def add_directive_header(self, sig: str) -> None:
        super().add_directive_header(sig)
        sourcename = self.get_sourcename()
        if inspect.isabstractmethod(self.object):
            self.add_line('   :abstractmethod:', sourcename)

        if safe_getattr(self.object, 'fget', None) and self.config.autodoc_typehints != 'none':
            try:
                signature = inspect.signature(self.object.fget,
                                              type_aliases=self.config.autodoc_type_aliases)
                if signature.return_annotation is not Parameter.empty:
                    objrepr = stringify_typehint(signature.return_annotation)
                    self.add_line('   :type: ' + objrepr, sourcename)
            except TypeError as exc:
                logger.warning(__("Failed to get a function signature for %s: %s"),
                               self.fullname, exc)
                return None
            except ValueError:
                return None


class NewTypeAttributeDocumenter(AttributeDocumenter):
    """
    Specialized Documenter subclass for NewTypes.

    Note: This must be invoked before MethodDocumenter because NewType is a kind of
    function object.
    """

    objtype = 'newvarattribute'
    directivetype = 'attribute'
    priority = MethodDocumenter.priority + 1

    @classmethod
    def can_document_member(cls, member: Any, membername: str, isattr: bool, parent: Any
                            ) -> bool:
        return not isinstance(parent, ModuleDocumenter) and inspect.isNewType(member)


def get_documenters(app: Sphinx) -> Dict[str, Type[Documenter]]:
    """Returns registered Documenter classes"""
    warnings.warn("get_documenters() is deprecated.", RemovedInSphinx50Warning, stacklevel=2)
    return app.registry.documenters


def autodoc_attrgetter(app: Sphinx, obj: Any, name: str, *defargs: Any) -> Any:
    """Alternative getattr() for types"""
    for typ, func in app.registry.autodoc_attrgettrs.items():
        if isinstance(obj, typ):
            return func(obj, name, *defargs)

    return safe_getattr(obj, name, *defargs)


def migrate_autodoc_member_order(app: Sphinx, config: Config) -> None:
    if config.autodoc_member_order == 'alphabetic':
        # RemovedInSphinx50Warning
        logger.warning(__('autodoc_member_order now accepts "alphabetical" '
                          'instead of "alphabetic". Please update your setting.'))
        config.autodoc_member_order = 'alphabetical'  # type: ignore


# for compatibility
from sphinx.ext.autodoc.deprecated import DataDeclarationDocumenter  # NOQA
from sphinx.ext.autodoc.deprecated import GenericAliasDocumenter  # NOQA
from sphinx.ext.autodoc.deprecated import InstanceAttributeDocumenter  # NOQA
from sphinx.ext.autodoc.deprecated import SingledispatchFunctionDocumenter  # NOQA
from sphinx.ext.autodoc.deprecated import SingledispatchMethodDocumenter  # NOQA
from sphinx.ext.autodoc.deprecated import SlotsAttributeDocumenter  # NOQA
from sphinx.ext.autodoc.deprecated import TypeVarDocumenter  # NOQA


def setup(app: Sphinx) -> Dict[str, Any]:
    app.add_autodocumenter(ModuleDocumenter)
    app.add_autodocumenter(ClassDocumenter)
    app.add_autodocumenter(ExceptionDocumenter)
    app.add_autodocumenter(DataDocumenter)
    app.add_autodocumenter(NewTypeDataDocumenter)
    app.add_autodocumenter(FunctionDocumenter)
    app.add_autodocumenter(DecoratorDocumenter)
    app.add_autodocumenter(MethodDocumenter)
    app.add_autodocumenter(AttributeDocumenter)
    app.add_autodocumenter(PropertyDocumenter)
    app.add_autodocumenter(NewTypeAttributeDocumenter)

    app.add_config_value('autoclass_content', 'class', True, ENUM('both', 'class', 'init'))
    app.add_config_value('autodoc_member_order', 'alphabetical', True,
                         ENUM('alphabetic', 'alphabetical', 'bysource', 'groupwise'))
    app.add_config_value('autodoc_class_signature', 'mixed', True, ENUM('mixed', 'separated'))
    app.add_config_value('autodoc_default_options', {}, True)
    app.add_config_value('autodoc_docstring_signature', True, True)
    app.add_config_value('autodoc_mock_imports', [], True)
    app.add_config_value('autodoc_typehints', "signature", True,
                         ENUM("signature", "description", "none", "both"))
    app.add_config_value('autodoc_typehints_description_target', 'all', True,
                         ENUM('all', 'documented'))
    app.add_config_value('autodoc_type_aliases', {}, True)
    app.add_config_value('autodoc_warningiserror', True, True)
    app.add_config_value('autodoc_inherit_docstrings', True, True)
    app.add_event('autodoc-before-process-signature')
    app.add_event('autodoc-process-docstring')
    app.add_event('autodoc-process-signature')
    app.add_event('autodoc-skip-member')
    app.add_event('autodoc-process-bases')

    app.connect('config-inited', migrate_autodoc_member_order, priority=800)

    app.setup_extension('sphinx.ext.autodoc.preserve_defaults')
    app.setup_extension('sphinx.ext.autodoc.type_comment')
    app.setup_extension('sphinx.ext.autodoc.typehints')

    return {'version': sphinx.__display_version__, 'parallel_read_safe': True}