Merge branch 'master' into master

9 files changed, 137 insertions, 8 deletions

diff --git a/astroid/brain/brain_builtin_inference.py b/astroid/brain/brain_builtin_inference.py
index 0008244c..b7659cc9 100644
--- a/astroid/brain/brain_builtin_inference.py
+++ b/astroid/brain/brain_builtin_inference.py
@@ -223,6 +223,8 @@ def _container_generic_transform(arg, context, klass, iterables, build_elts):
             # TODO: Does not handle deduplication for sets.
             elts = []
             for element in arg.elts:
+                if not element:
+                    continue
                 inferred = helpers.safe_infer(element, context=context)
                 if inferred:
                     evaluated_object = nodes.EvaluatedObject(
diff --git a/astroid/brain/brain_collections.py b/astroid/brain/brain_collections.py
index 6594e0c7..229969c5 100644
--- a/astroid/brain/brain_collections.py
+++ b/astroid/brain/brain_collections.py
@@ -4,6 +4,7 @@
 # Copyright (c) 2017 Derek Gustafson <degustaf@gmail.com>
 # Copyright (c) 2018 Ioana Tagirta <ioana.tagirta@gmail.com>
 # Copyright (c) 2019 Hugo van Kemenade <hugovk@users.noreply.github.com>
+# Copyright (c) 2021 Julien Palard <julien@palard.fr>
 
 # 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
@@ -12,6 +13,9 @@ import sys
 import astroid
 
 
+PY39 = sys.version_info >= (3, 9)
+
+
 def _collections_transform():
     return astroid.parse(
         """
@@ -61,6 +65,10 @@ def _deque_mock():
         def __mul__(self, other): pass
         def __imul__(self, other): pass
         def __rmul__(self, other): pass"""
+    if PY39:
+        base_deque_class += """
+        @classmethod
+        def __class_getitem__(self, item): pass"""
     return base_deque_class
 
 
diff --git a/astroid/brain/brain_numpy_core_umath.py b/astroid/brain/brain_numpy_core_umath.py
index 1955e80e..73613b86 100644
--- a/astroid/brain/brain_numpy_core_umath.py
+++ b/astroid/brain/brain_numpy_core_umath.py
@@ -106,6 +106,7 @@ def numpy_core_umath_transform():
     trunc = FakeUfuncOneArg()
 
     # Two args functions with optional kwargs
+    add = FakeUfuncTwoArgs()
     bitwise_and = FakeUfuncTwoArgs()
     bitwise_or = FakeUfuncTwoArgs()
     bitwise_xor = FakeUfuncTwoArgs()
@@ -133,6 +134,7 @@ def numpy_core_umath_transform():
     logical_xor = FakeUfuncTwoArgs()
     maximum = FakeUfuncTwoArgs()
     minimum = FakeUfuncTwoArgs()
+    multiply = FakeUfuncTwoArgs()
     nextafter = FakeUfuncTwoArgs()
     not_equal = FakeUfuncTwoArgs()
     power = FakeUfuncTwoArgs()
diff --git a/astroid/brain/brain_six.py b/astroid/brain/brain_six.py
index 389037f2..a998213f 100644
--- a/astroid/brain/brain_six.py
+++ b/astroid/brain/brain_six.py
@@ -22,6 +22,7 @@ from astroid import nodes
 
 
 SIX_ADD_METACLASS = "six.add_metaclass"
+SIX_WITH_METACLASS = "six.with_metaclass"
 
 
 def _indent(text, prefix, predicate=None):
@@ -190,6 +191,39 @@ def transform_six_add_metaclass(node):
             return node
 
 
+def _looks_like_nested_from_six_with_metaclass(node):
+    if len(node.bases) != 1:
+        return False
+    base = node.bases[0]
+    if not isinstance(base, nodes.Call):
+        return False
+    try:
+        if hasattr(base.func, "expr"):
+            # format when explicit 'six.with_metaclass' is used
+            mod = base.func.expr.name
+            func = base.func.attrname
+            func = "{}.{}".format(mod, func)
+        else:
+            # format when 'with_metaclass' is used directly (local import from six)
+            # check reference module to avoid 'with_metaclass' name clashes
+            mod = base.parent.parent
+            import_from = mod.locals["with_metaclass"][0]
+            func = "{}.{}".format(import_from.modname, base.func.name)
+    except (AttributeError, KeyError, IndexError):
+        return False
+    return func == SIX_WITH_METACLASS
+
+
+def transform_six_with_metaclass(node):
+    """Check if the given class node is defined with *six.with_metaclass*
+
+    If so, inject its argument as the metaclass of the underlying class.
+    """
+    call = node.bases[0]
+    node._metaclass = call.args[0]
+    node.bases = call.args[1:]
+
+
 register_module_extender(MANAGER, "six", six_moves_transform)
 register_module_extender(
     MANAGER, "requests.packages.urllib3.packages.six", six_moves_transform
@@ -200,3 +234,8 @@ MANAGER.register_transform(
     transform_six_add_metaclass,
     _looks_like_decorated_with_six_add_metaclass,
 )
+MANAGER.register_transform(
+    nodes.ClassDef,
+    transform_six_with_metaclass,
+    _looks_like_nested_from_six_with_metaclass,
+)
diff --git a/astroid/brain/brain_subprocess.py b/astroid/brain/brain_subprocess.py
index bc35704f..c19b32b1 100644
--- a/astroid/brain/brain_subprocess.py
+++ b/astroid/brain/brain_subprocess.py
@@ -14,6 +14,7 @@ import textwrap
 import astroid
 
 
+PY39 = sys.version_info >= (3, 9)
 PY37 = sys.version_info >= (3, 7)
 PY36 = sys.version_info >= (3, 6)
 
@@ -147,6 +148,12 @@ def _subprocess_transform():
             "py3_args": py3_args,
         }
     )
+    if PY39:
+        code += """
+    @classmethod
+    def __class_getitem__(cls, item):
+        pass
+        """
 
     init_lines = textwrap.dedent(init).splitlines()
     indented_init = "\n".join(" " * 4 + line for line in init_lines)
diff --git a/astroid/brain/brain_type.py b/astroid/brain/brain_type.py
new file mode 100644
index 00000000..4e82813f
--- /dev/null
+++ b/astroid/brain/brain_type.py
@@ -0,0 +1,64 @@
+# -*- coding: utf-8 -*-
+"""
+Astroid hooks for type support.
+
+Starting from python3.9, type object behaves as it had __class_getitem__ method.
+However it was not possible to simply add this method inside type's body, otherwise
+all types would also have this method. In this case it would have been possible
+to write str[int].
+Guido Van Rossum proposed a hack to handle this in the interpreter:
+https://github.com/python/cpython/blob/master/Objects/abstract.c#L186-L189
+
+This brain follows the same logic. It is no wise to add permanently the __class_getitem__ method 
+to the type object. Instead we choose to add it only in the case of a subscript node
+which inside name node is type. 
+Doing this type[int] is allowed whereas str[int] is not.
+
+Thanks to Lukasz Langa for fruitful discussion.
+"""
+import sys
+
+from astroid import MANAGER, extract_node, inference_tip, nodes
+
+
+PY39 = sys.version_info >= (3, 9)
+
+
+def _looks_like_type_subscript(node):
+    """
+    Try to figure out if a Name node is used inside a type related subscript
+
+    :param node: node to check
+    :type node: astroid.node_classes.NodeNG
+    :return: true if the node is a Name node inside a type related subscript
+    :rtype: bool
+    """
+    if isinstance(node, nodes.Name) and isinstance(node.parent, nodes.Subscript):
+        return node.name == "type"
+    return False
+
+
+def infer_type_sub(node, context=None):
+    """
+    Infer a type[...] subscript
+
+    :param node: node to infer
+    :type node: astroid.node_classes.NodeNG
+    :param context: inference context
+    :type context: astroid.context.InferenceContext
+    :return: the inferred node
+    :rtype: nodes.NodeNG
+    """
+    class_src = """
+    class type:
+        def __class_getitem__(cls, key):
+            return cls
+     """
+    node = extract_node(class_src)
+    return node.infer(context=context)
+
+
+if PY39:
+    MANAGER.register_transform(
+        nodes.Name, inference_tip(infer_type_sub), _looks_like_type_subscript
+    )
diff --git a/astroid/context.py b/astroid/context.py
index f1e06974..4bda945f 100644
--- a/astroid/context.py
+++ b/astroid/context.py
@@ -29,8 +29,10 @@ class InferenceContext:
         "extra_context",
     )
 
+    maximum_path_visit = 3
+
     def __init__(self, path=None, inferred=None):
-        self.path = path or set()
+        self.path = path or dict()
         """
         :type: set(tuple(NodeNG, optional(str)))
 
@@ -87,10 +89,10 @@ class InferenceContext:
         Allows one to see if the given node has already
         been looked at for this inference context"""
         name = self.lookupname
-        if (node, name) in self.path:
+        if self.path.get((node, name), 0) >= self.maximum_path_visit:
             return True
 
-        self.path.add((node, name))
+        self.path[(node, name)] = self.path.setdefault((node, name), 0) + 1
         return False
 
     def clone(self):
@@ -108,7 +110,7 @@ class InferenceContext:
 
     @contextlib.contextmanager
     def restore_path(self):
-        path = set(self.path)
+        path = dict(self.path)
         yield
         self.path = path
 
diff --git a/astroid/node_classes.py b/astroid/node_classes.py
index 86529e5a..62438e62 100644
--- a/astroid/node_classes.py
+++ b/astroid/node_classes.py
@@ -2125,6 +2125,11 @@ class AugAssign(mixins.AssignTypeMixin, Statement):
         yield self.target
         yield self.value
 
+    def _get_yield_nodes_skip_lambdas(self):
+        """An AugAssign node can contain a Yield node in the value"""
+        yield from self.value._get_yield_nodes_skip_lambdas()
+        yield from super()._get_yield_nodes_skip_lambdas()
+
 
 class Repr(NodeNG):
     """Class representing an :class:`ast.Repr` node.
diff --git a/astroid/rebuilder.py b/astroid/rebuilder.py
index 3fc1a83f..e56abbf8 100644
--- a/astroid/rebuilder.py
+++ b/astroid/rebuilder.py
@@ -238,7 +238,7 @@ class TreeRebuilder:
 
         return type_object.value
 
-    def check_function_type_comment(self, node):
+    def check_function_type_comment(self, node, parent):
         type_comment = getattr(node, "type_comment", None)
         if not type_comment:
             return None
@@ -251,10 +251,10 @@ class TreeRebuilder:
 
         returns = None
         argtypes = [
-            self.visit(elem, node) for elem in (type_comment_ast.argtypes or [])
+            self.visit(elem, parent) for elem in (type_comment_ast.argtypes or [])
         ]
         if type_comment_ast.returns:
-            returns = self.visit(type_comment_ast.returns, node)
+            returns = self.visit(type_comment_ast.returns, parent)
 
         return returns, argtypes
 
@@ -615,7 +615,7 @@ class TreeRebuilder:
             returns = None
 
         type_comment_args = type_comment_returns = None
-        type_comment_annotation = self.check_function_type_comment(node)
+        type_comment_annotation = self.check_function_type_comment(node, newnode)
         if type_comment_annotation:
             type_comment_returns, type_comment_args = type_comment_annotation
         newnode.postinit(