bases.py

# Copyright (c) 2009-2011, 2013-2014 LOGILAB S.A. (Paris, FRANCE) <contact@logilab.fr>
# Copyright (c) 2012 FELD Boris <lothiraldan@gmail.com>
# Copyright (c) 2014-2018 Claudiu Popa <pcmanticore@gmail.com>
# Copyright (c) 2014 Google, Inc.
# Copyright (c) 2014 Eevee (Alex Munroe) <amunroe@yelp.com>
# Copyright (c) 2015-2016 Ceridwen <ceridwenv@gmail.com>
# Copyright (c) 2015 Florian Bruhin <me@the-compiler.org>
# Copyright (c) 2016-2017 Derek Gustafson <degustaf@gmail.com>
# Copyright (c) 2017 Calen Pennington <calen.pennington@gmail.com>
# Copyright (c) 2018 Bryce Guinta <bryce.paul.guinta@gmail.com>
# Copyright (c) 2018 Nick Drozd <nicholasdrozd@gmail.com>
# Copyright (c) 2018 Daniel Colascione <dancol@dancol.org>

# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
# For details: https://github.com/PyCQA/astroid/blob/master/COPYING.LESSER

"""This module contains base classes and functions for the nodes and some
inference utils.
"""

import builtins
import collections

from astroid import context as contextmod
from astroid import exceptions
from astroid import util

objectmodel = util.lazy_import("interpreter.objectmodel")
helpers = util.lazy_import("helpers")
BUILTINS = builtins.__name__
manager = util.lazy_import("manager")
MANAGER = manager.AstroidManager()

# TODO: check if needs special treatment
BUILTINS = "builtins"
BOOL_SPECIAL_METHOD = "__bool__"

PROPERTIES = {BUILTINS + ".property", "abc.abstractproperty"}
# List of possible property names. We use this list in order
# to see if a method is a property or not. This should be
# pretty reliable and fast, the alternative being to check each
# decorator to see if its a real property-like descriptor, which
# can be too complicated.
# Also, these aren't qualified, because each project can
# define them, we shouldn't expect to know every possible
# property-like decorator!
POSSIBLE_PROPERTIES = {
    "cached_property",
    "cachedproperty",
    "lazyproperty",
    "lazy_property",
    "reify",
    "lazyattribute",
    "lazy_attribute",
    "LazyProperty",
    "lazy",
    "cache_readonly",
}


def _is_property(meth):
    if PROPERTIES.intersection(meth.decoratornames()):
        return True
    stripped = {
        name.split(".")[-1]
        for name in meth.decoratornames()
        if name is not util.Uninferable
    }
    if any(name in stripped for name in POSSIBLE_PROPERTIES):
        return True

    # Lookup for subclasses of *property*
    if not meth.decorators:
        return False
    for decorator in meth.decorators.nodes or ():
        inferred = helpers.safe_infer(decorator)
        if inferred is None or inferred is util.Uninferable:
            continue
        if inferred.__class__.__name__ == "ClassDef":
            for base_class in inferred.bases:
                if base_class.__class__.__name__ != "Name":
                    continue
                module, _ = base_class.lookup(base_class.name)
                if module.name == BUILTINS and base_class.name == "property":
                    return True

    return False


class Proxy:
    """a simple proxy object

    Note:

    Subclasses of this object will need a custom __getattr__
    if new instance attributes are created. See the Const class
    """

    _proxied = None  # proxied object may be set by class or by instance

    def __init__(self, proxied=None):
        if proxied is not None:
            self._proxied = proxied

    def __getattr__(self, name):
        if name == "_proxied":
            return getattr(self.__class__, "_proxied")
        if name in self.__dict__:
            return self.__dict__[name]
        return getattr(self._proxied, name)

    def infer(self, context=None):
        yield self


def _infer_stmts(stmts, context, frame=None):
    """Return an iterator on statements inferred by each statement in *stmts*."""
    inferred = False
    if context is not None:
        name = context.lookupname
        context = context.clone()
    else:
        name = None
        context = contextmod.InferenceContext()

    for stmt in stmts:
        if stmt is util.Uninferable:
            yield stmt
            inferred = True
            continue
        context.lookupname = stmt._infer_name(frame, name)
        try:
            for inferred in stmt.infer(context=context):
                yield inferred
                inferred = True
        except exceptions.NameInferenceError:
            continue
        except exceptions.InferenceError:
            yield util.Uninferable
            inferred = True
    if not inferred:
        raise exceptions.InferenceError(
            "Inference failed for all members of {stmts!r}.",
            stmts=stmts,
            frame=frame,
            context=context,
        )


def _infer_method_result_truth(instance, method_name, context):
    # Get the method from the instance and try to infer
    # its return's truth value.
    meth = next(instance.igetattr(method_name, context=context), None)
    if meth and hasattr(meth, "infer_call_result"):
        if not meth.callable():
            return util.Uninferable
        try:
            for value in meth.infer_call_result(instance, context=context):
                if value is util.Uninferable:
                    return value

                inferred = next(value.infer(context=context))
                return inferred.bool_value()
        except exceptions.InferenceError:
            pass
    return util.Uninferable


class BaseInstance(Proxy):
    """An instance base class, which provides lookup methods for potential instances."""

    special_attributes = None

    def display_type(self):
        return "Instance of"

    def getattr(self, name, context=None, lookupclass=True):
        try:
            values = self._proxied.instance_attr(name, context)
        except exceptions.AttributeInferenceError as exc:
            if self.special_attributes and name in self.special_attributes:
                return [self.special_attributes.lookup(name)]

            if lookupclass:
                # Class attributes not available through the instance
                # unless they are explicitly defined.
                return self._proxied.getattr(name, context, class_context=False)

            raise exceptions.AttributeInferenceError(
                target=self, attribute=name, context=context
            ) from exc
        # since we've no context information, return matching class members as
        # well
        if lookupclass:
            try:
                return values + self._proxied.getattr(
                    name, context, class_context=False
                )
            except exceptions.AttributeInferenceError:
                pass
        return values

    def igetattr(self, name, context=None):
        """inferred getattr"""
        if not context:
            context = contextmod.InferenceContext()
        try:
            # avoid recursively inferring the same attr on the same class
            if context.push((self._proxied, name)):
                raise exceptions.InferenceError(
                    message="Cannot infer the same attribute again",
                    node=self,
                    context=context,
                )

            # XXX frame should be self._proxied, or not ?
            get_attr = self.getattr(name, context, lookupclass=False)
            yield from _infer_stmts(
                self._wrap_attr(get_attr, context), context, frame=self
            )
        except exceptions.AttributeInferenceError as error:
            try:
                # fallback to class.igetattr since it has some logic to handle
                # descriptors
                # But only if the _proxied is the Class.
                if self._proxied.__class__.__name__ != "ClassDef":
                    raise
                attrs = self._proxied.igetattr(name, context, class_context=False)
                yield from self._wrap_attr(attrs, context)
            except exceptions.AttributeInferenceError as error:
                raise exceptions.InferenceError(**vars(error)) from error

    def _wrap_attr(self, attrs, context=None):
        """wrap bound methods of attrs in a InstanceMethod proxies"""
        for attr in attrs:
            if isinstance(attr, UnboundMethod):
                if _is_property(attr):
                    yield from attr.infer_call_result(self, context)
                else:
                    yield BoundMethod(attr, self)
            elif hasattr(attr, "name") and attr.name == "<lambda>":
                if attr.args.args and attr.args.args[0].name == "self":
                    yield BoundMethod(attr, self)
                    continue
                yield attr
            else:
                yield attr

    def infer_call_result(self, caller, context=None):
        """infer what a class instance is returning when called"""
        context = contextmod.bind_context_to_node(context, self)
        inferred = False
        for node in self._proxied.igetattr("__call__", context):
            if node is util.Uninferable or not node.callable():
                continue
            for res in node.infer_call_result(caller, context):
                inferred = True
                yield res
        if not inferred:
            raise exceptions.InferenceError(node=self, caller=caller, context=context)


class Instance(BaseInstance):
    """A special node representing a class instance."""

    # pylint: disable=unnecessary-lambda
    special_attributes = util.lazy_descriptor(lambda: objectmodel.InstanceModel())

    def __repr__(self):
        return "<Instance of %s.%s at 0x%s>" % (
            self._proxied.root().name,
            self._proxied.name,
            id(self),
        )

    def __str__(self):
        return "Instance of %s.%s" % (self._proxied.root().name, self._proxied.name)

    def callable(self):
        try:
            self._proxied.getattr("__call__", class_context=False)
            return True
        except exceptions.AttributeInferenceError:
            return False

    def pytype(self):
        return self._proxied.qname()

    def display_type(self):
        return "Instance of"

    def bool_value(self):
        """Infer the truth value for an Instance

        The truth value of an instance is determined by these conditions:

           * if it implements __bool__ on Python 3 or __nonzero__
             on Python 2, then its bool value will be determined by
             calling this special method and checking its result.
           * when this method is not defined, __len__() is called, if it
             is defined, and the object is considered true if its result is
             nonzero. If a class defines neither __len__() nor __bool__(),
             all its instances are considered true.
        """
        context = contextmod.InferenceContext()
        context.callcontext = contextmod.CallContext(args=[])
        context.boundnode = self

        try:
            result = _infer_method_result_truth(self, BOOL_SPECIAL_METHOD, context)
        except (exceptions.InferenceError, exceptions.AttributeInferenceError):
            # Fallback to __len__.
            try:
                result = _infer_method_result_truth(self, "__len__", context)
            except (exceptions.AttributeInferenceError, exceptions.InferenceError):
                return True
        return result

    # This is set in inference.py.
    def getitem(self, index, context=None):
        pass


class UnboundMethod(Proxy):
    """a special node representing a method not bound to an instance"""

    # pylint: disable=unnecessary-lambda
    special_attributes = util.lazy_descriptor(lambda: objectmodel.UnboundMethodModel())

    def __repr__(self):
        frame = self._proxied.parent.frame()
        return "<%s %s of %s at 0x%s" % (
            self.__class__.__name__,
            self._proxied.name,
            frame.qname(),
            id(self),
        )

    def implicit_parameters(self):
        return 0

    def is_bound(self):
        return False

    def getattr(self, name, context=None):
        if name in self.special_attributes:
            return [self.special_attributes.lookup(name)]
        return self._proxied.getattr(name, context)

    def igetattr(self, name, context=None):
        if name in self.special_attributes:
            return iter((self.special_attributes.lookup(name),))
        return self._proxied.igetattr(name, context)

    def infer_call_result(self, caller, context):
        """
        The boundnode of the regular context with a function called
        on ``object.__new__`` will be of type ``object``,
        which is incorrect for the argument in general.
        If no context is given the ``object.__new__`` call argument will
        correctly inferred except when inside a call that requires
        the additional context (such as a classmethod) of the boundnode
        to determine which class the method was called from
        """

        # If we're unbound method __new__ of builtin object, the result is an
        # instance of the class given as first argument.
        if (
            self._proxied.name == "__new__"
            and self._proxied.parent.frame().qname() == "%s.object" % BUILTINS
        ):
            if caller.args:
                node_context = context.extra_context.get(caller.args[0])
                infer = caller.args[0].infer(context=node_context)
            else:
                infer = []
            return (Instance(x) if x is not util.Uninferable else x for x in infer)
        return self._proxied.infer_call_result(caller, context)

    def bool_value(self):
        return True


class BoundMethod(UnboundMethod):
    """a special node representing a method bound to an instance"""

    # pylint: disable=unnecessary-lambda
    special_attributes = util.lazy_descriptor(lambda: objectmodel.BoundMethodModel())

    def __init__(self, proxy, bound):
        UnboundMethod.__init__(self, proxy)
        self.bound = bound

    def implicit_parameters(self):
        return 1

    def is_bound(self):
        return True

    def _infer_type_new_call(self, caller, context):
        """Try to infer what type.__new__(mcs, name, bases, attrs) returns.

        In order for such call to be valid, the metaclass needs to be
        a subtype of ``type``, the name needs to be a string, the bases
        needs to be a tuple of classes
        """
        # pylint: disable=import-outside-toplevel; circular import
        from astroid import node_classes

        # Verify the metaclass
        mcs = next(caller.args[0].infer(context=context))
        if mcs.__class__.__name__ != "ClassDef":
            # Not a valid first argument.
            return None
        if not mcs.is_subtype_of("%s.type" % BUILTINS):
            # Not a valid metaclass.
            return None

        # Verify the name
        name = next(caller.args[1].infer(context=context))
        if name.__class__.__name__ != "Const":
            # Not a valid name, needs to be a const.
            return None
        if not isinstance(name.value, str):
            # Needs to be a string.
            return None

        # Verify the bases
        bases = next(caller.args[2].infer(context=context))
        if bases.__class__.__name__ != "Tuple":
            # Needs to be a tuple.
            return None
        inferred_bases = [next(elt.infer(context=context)) for elt in bases.elts]
        if any(base.__class__.__name__ != "ClassDef" for base in inferred_bases):
            # All the bases needs to be Classes
            return None

        # Verify the attributes.
        attrs = next(caller.args[3].infer(context=context))
        if attrs.__class__.__name__ != "Dict":
            # Needs to be a dictionary.
            return None
        cls_locals = collections.defaultdict(list)
        for key, value in attrs.items:
            key = next(key.infer(context=context))
            value = next(value.infer(context=context))
            # Ignore non string keys
            if key.__class__.__name__ == "Const" and isinstance(key.value, str):
                cls_locals[key.value].append(value)

        # Build the class from now.
        cls = mcs.__class__(
            name=name.value,
            lineno=caller.lineno,
            col_offset=caller.col_offset,
            parent=caller,
        )
        empty = node_classes.Pass()
        cls.postinit(
            bases=bases.elts,
            body=[empty],
            decorators=[],
            newstyle=True,
            metaclass=mcs,
            keywords=[],
        )
        cls.locals = cls_locals
        return cls

    def infer_call_result(self, caller, context=None):
        context = contextmod.bind_context_to_node(context, self.bound)
        if (
            self.bound.__class__.__name__ == "ClassDef"
            and self.bound.name == "type"
            and self.name == "__new__"
            and len(caller.args) == 4
        ):
            # Check if we have a ``type.__new__(mcs, name, bases, attrs)`` call.
            new_cls = self._infer_type_new_call(caller, context)
            if new_cls:
                return iter((new_cls,))

        return super(BoundMethod, self).infer_call_result(caller, context)

    def bool_value(self):
        return True


class Generator(BaseInstance):
    """a special node representing a generator.

    Proxied class is set once for all in raw_building.
    """

    # pylint: disable=unnecessary-lambda
    special_attributes = util.lazy_descriptor(lambda: objectmodel.GeneratorModel())

    # pylint: disable=super-init-not-called
    def __init__(self, parent=None):
        self.parent = parent

    def callable(self):
        return False

    def pytype(self):
        return "%s.generator" % BUILTINS

    def display_type(self):
        return "Generator"

    def bool_value(self):
        return True

    def __repr__(self):
        return "<Generator(%s) l.%s at 0x%s>" % (
            self._proxied.name,
            self.lineno,
            id(self),
        )

    def __str__(self):
        return "Generator(%s)" % (self._proxied.name)


class AsyncGenerator(Generator):
    """Special node representing an async generator"""

    def pytype(self):
        return "%s.async_generator" % BUILTINS

    def display_type(self):
        return "AsyncGenerator"

    def __repr__(self):
        return "<AsyncGenerator(%s) l.%s at 0x%s>" % (
            self._proxied.name,
            self.lineno,
            id(self),
        )

    def __str__(self):
        return "AsyncGenerator(%s)" % (self._proxied.name)