Merge branch 'master' into bug_pylint_2721

11 files changed, 225 insertions, 10 deletions

diff --git a/astroid/__pkginfo__.py b/astroid/__pkginfo__.py
index 55e89629..d3cb4705 100644
--- a/astroid/__pkginfo__.py
+++ b/astroid/__pkginfo__.py
@@ -26,7 +26,7 @@ install_requires = [
     "six",
     "wrapt",
     'typing;python_version<"3.5"',
-    'typed-ast>=1.3.0;implementation_name== "cpython"',
+    'typed-ast>=1.3.0;implementation_name== "cpython" and python_version<"3.8"',
 ]
 
 # pylint: disable=redefined-builtin; why license is a builtin anyway?
diff --git a/astroid/as_string.py b/astroid/as_string.py
index 7042272f..9d92b3cf 100644
--- a/astroid/as_string.py
+++ b/astroid/as_string.py
@@ -611,6 +611,12 @@ class AsStringVisitor3(AsStringVisitor):
             super(AsStringVisitor3, self).visit_comprehension(node),
         )
 
+    def visit_namedexpr(self, node):
+        """Return an assignment expression node as string"""
+        target = node.target.accept(self)
+        value = node.value.accept(self)
+        return "%s := %s" % (target, value)
+
 
 def _import_string(names):
     """return a list of (name, asname) formatted as a string"""
diff --git a/astroid/inference.py b/astroid/inference.py
index 16346a77..1ea45248 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -71,6 +71,11 @@ def _infer_sequence_helper(node, context=None):
             if not hasattr(starred, "elts"):
                 raise exceptions.InferenceError(node=node, context=context)
             values.extend(_infer_sequence_helper(starred))
+        elif isinstance(elt, nodes.NamedExpr):
+            value = helpers.safe_infer(elt.value, context)
+            if not value:
+                raise exceptions.InferenceError(node=node, context=context)
+            values.append(value)
         else:
             values.append(elt)
     return values
@@ -78,9 +83,10 @@ def _infer_sequence_helper(node, context=None):
 
 @decorators.raise_if_nothing_inferred
 def infer_sequence(self, context=None):
-    if not any(isinstance(e, nodes.Starred) for e in self.elts):
-        yield self
-    else:
+    has_starred_named_expr = any(
+        isinstance(e, (nodes.Starred, nodes.NamedExpr)) for e in self.elts
+    )
+    if has_starred_named_expr:
         values = _infer_sequence_helper(self, context)
         new_seq = type(self)(
             lineno=self.lineno, col_offset=self.col_offset, parent=self.parent
@@ -88,6 +94,8 @@ def infer_sequence(self, context=None):
         new_seq.postinit(values)
 
         yield new_seq
+    else:
+        yield self
 
 
 nodes.List._infer = infer_sequence
@@ -897,3 +905,32 @@ def _populate_context_lookup(call, context):
     for keyword in keywords:
         context_lookup[keyword.value] = context
     return context_lookup
+
+
+@decorators.raise_if_nothing_inferred
+def infer_ifexp(self, context=None):
+    """Support IfExp inference
+
+    If we can't infer the truthiness of the condition, we default
+    to inferring both branches. Otherwise, we infer either branch
+    depending on the condition.
+    """
+    both_branches = False
+    try:
+        test = next(self.test.infer(context=context))
+    except exceptions.InferenceError:
+        both_branches = True
+    else:
+        if test is not util.Uninferable:
+            if test.bool_value():
+                yield from self.body.infer(context=context)
+            else:
+                yield from self.orelse.infer(context=context)
+        else:
+            both_branches = True
+    if both_branches:
+        yield from self.body.infer(context=context)
+        yield from self.orelse.infer(context=context)
+
+
+nodes.IfExp._infer = infer_ifexp
diff --git a/astroid/node_classes.py b/astroid/node_classes.py
index 2e39b060..44fe3df4 100644
--- a/astroid/node_classes.py
+++ b/astroid/node_classes.py
@@ -31,8 +31,8 @@ import abc
 import builtins as builtins_mod
 import itertools
 import pprint
-from functools import lru_cache
-from functools import singledispatch as _singledispatch
+import sys
+from functools import lru_cache, singledispatch as _singledispatch
 
 from astroid import as_string
 from astroid import bases
@@ -46,6 +46,7 @@ from astroid import util
 
 BUILTINS = builtins_mod.__name__
 MANAGER = manager.AstroidManager()
+PY38 = sys.version_info[:2] >= (3, 8)
 
 
 def _is_const(value):
@@ -1200,6 +1201,10 @@ class LookupMixIn:
                 _stmt_parents = [stmt.parent]
                 continue
 
+            if isinstance(assign_type, NamedExpr):
+                _stmts = [node]
+                continue
+
             # XXX comment various branches below!!!
             try:
                 pindex = _stmt_parents.index(stmt.parent)
@@ -4622,6 +4627,31 @@ class JoinedStr(NodeNG):
         yield from self.values
 
 
+class NamedExpr(mixins.AssignTypeMixin, NodeNG):
+    """Represents the assignment from the assignment expression
+
+    >>> module = astroid.parse('if a := 1: pass')
+    >>> module.body[0].test
+    <NamedExpr l.1 at 0x7f23b2e4ed30>
+    """
+
+    _astroid_fields = ("target", "value")
+    target = None
+    """The assignment target
+
+    :type: Name
+    """
+    value = None
+    """The value that gets assigned in the expression
+
+    :type: NodeNG
+    """
+
+    def postinit(self, target, value):
+        self.target = target
+        self.value = value
+
+
 class Unknown(mixins.AssignTypeMixin, NodeNG):
     """This node represents a node in a constructed AST where
     introspection is not possible.  At the moment, it's only used in
@@ -4649,6 +4679,8 @@ CONST_CLS = {
     type(None): Const,
     type(NotImplemented): Const,
 }
+if PY38:
+    CONST_CLS[type(...)] = Const
 
 
 def _update_const_classes():
diff --git a/astroid/nodes.py b/astroid/nodes.py
index 20672593..bf6911ac 100644
--- a/astroid/nodes.py
+++ b/astroid/nodes.py
@@ -59,6 +59,7 @@ from astroid.node_classes import (
     Keyword,
     List,
     Name,
+    NamedExpr,
     Nonlocal,
     Pass,
     Print,
@@ -149,6 +150,7 @@ ALL_NODE_CLASSES = (
     List,
     ListComp,
     Name,
+    NamedExpr,
     Nonlocal,
     Module,
     Pass,
diff --git a/astroid/protocols.py b/astroid/protocols.py
index bf497ff1..b598ec3d 100644
--- a/astroid/protocols.py
+++ b/astroid/protocols.py
@@ -572,6 +572,23 @@ def with_assigned_stmts(self, node=None, context=None, assign_path=None):
 nodes.With.assigned_stmts = with_assigned_stmts
 
 
+@decorators.raise_if_nothing_inferred
+def named_expr_assigned_stmts(self, node, context=None, assign_path=None):
+    """Infer names and other nodes from an assignment expression"""
+    if self.target == node:
+        yield from self.value.infer(context=context)
+    else:
+        raise exceptions.InferenceError(
+            "Cannot infer NamedExpr node {node!r}",
+            node=self,
+            assign_path=assign_path,
+            context=context,
+        )
+
+
+nodes.NamedExpr.assigned_stmts = named_expr_assigned_stmts
+
+
 @decorators.yes_if_nothing_inferred
 def starred_assigned_stmts(self, node=None, context=None, assign_path=None):
     """
diff --git a/astroid/raw_building.py b/astroid/raw_building.py
index 60000fdb..d9a1dc47 100644
--- a/astroid/raw_building.py
+++ b/astroid/raw_building.py
@@ -34,6 +34,9 @@ MANAGER = manager.AstroidManager()
 
 _CONSTANTS = tuple(node_classes.CONST_CLS)
 _BUILTINS = vars(builtins)
+TYPE_NONE = type(None)
+TYPE_NOTIMPLEMENTED = type(NotImplemented)
+TYPE_ELLIPSIS = type(...)
 
 
 def _io_discrepancy(member):
@@ -390,12 +393,15 @@ def _astroid_bootstrapping():
 
     # pylint: disable=redefined-outer-name
     for cls, node_cls in node_classes.CONST_CLS.items():
-        if cls is type(None):
+        if cls is TYPE_NONE:
             proxy = build_class("NoneType")
             proxy.parent = astroid_builtin
-        elif cls is type(NotImplemented):
+        elif cls is TYPE_NOTIMPLEMENTED:
             proxy = build_class("NotImplementedType")
             proxy.parent = astroid_builtin
+        elif cls is TYPE_ELLIPSIS:
+            proxy = build_class("Ellipsis")
+            proxy.parent = astroid_builtin
         else:
             proxy = astroid_builtin.getattr(cls.__name__)[0]
         if cls in (dict, list, set, tuple):
@@ -425,8 +431,8 @@ def _astroid_bootstrapping():
         types.GetSetDescriptorType,
         types.GeneratorType,
         types.MemberDescriptorType,
-        type(None),
-        type(NotImplemented),
+        TYPE_NONE,
+        TYPE_NOTIMPLEMENTED,
         types.FunctionType,
         types.MethodType,
         types.BuiltinFunctionType,
diff --git a/astroid/rebuilder.py b/astroid/rebuilder.py
index c18893d8..a60785c4 100644
--- a/astroid/rebuilder.py
+++ b/astroid/rebuilder.py
@@ -1063,6 +1063,13 @@ class TreeRebuilder3(TreeRebuilder):
         )
         return newnode
 
+    def visit_namedexpr(self, node, parent):
+        newnode = nodes.NamedExpr(node.lineno, node.col_offset, parent)
+        newnode.postinit(
+            self.visit(node.target, newnode), self.visit(node.value, newnode)
+        )
+        return newnode
+
 
 if sys.version_info >= (3, 0):
     TreeRebuilder = TreeRebuilder3
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index eff9b148..1f9c7e44 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -5260,5 +5260,34 @@ def test_subclass_of_exception():
     assert isinstance(args, nodes.Tuple)
 
 
+def test_ifexp_inference():
+    code = """
+    def truth_branch():
+        return 1 if True else 2
+
+    def false_branch():
+        return 1 if False else 2
+
+    def both_branches():
+        return 1 if unknown() else 2
+
+    truth_branch() #@
+    false_branch() #@
+    both_branches() #@
+    """
+    ast_nodes = extract_node(code)
+    first = next(ast_nodes[0].infer())
+    assert isinstance(first, nodes.Const)
+    assert first.value == 1
+
+    second = next(ast_nodes[1].infer())
+    assert isinstance(second, nodes.Const)
+    assert second.value == 2
+
+    third = list(ast_nodes[2].infer())
+    assert isinstance(third, list)
+    assert [third[0].value, third[1].value] == [1, 2]
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/astroid/tests/unittest_nodes.py b/astroid/tests/unittest_nodes.py
index 800eef3a..96a7f830 100644
--- a/astroid/tests/unittest_nodes.py
+++ b/astroid/tests/unittest_nodes.py
@@ -1134,5 +1134,30 @@ def test_f_string_correct_line_numbering():
     assert node.last_child().last_child().lineno == 5
 
 
+@pytest.mark.skipif(
+    sys.version_info[:2] < (3, 8), reason="needs assignment expressions"
+)
+def test_assignment_expression():
+    code = """
+    if __(a := 1):
+        pass
+    if __(b := test):
+        pass
+    """
+    first, second = astroid.extract_node(code)
+
+    assert isinstance(first.target, nodes.AssignName)
+    assert first.target.name == "a"
+    assert isinstance(first.value, nodes.Const)
+    assert first.value.value == 1
+    assert first.as_string() == "a := 1"
+
+    assert isinstance(second.target, nodes.AssignName)
+    assert second.target.name == "b"
+    assert isinstance(second.value, nodes.Name)
+    assert second.value.name == "test"
+    assert second.as_string() == "b := test"
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/astroid/tests/unittest_protocols.py b/astroid/tests/unittest_protocols.py
index 79648dcf..e05c43cc 100644
--- a/astroid/tests/unittest_protocols.py
+++ b/astroid/tests/unittest_protocols.py
@@ -213,5 +213,59 @@ class ProtocolTests(unittest.TestCase):
         parsed.accept(Visitor())
 
 
+def test_named_expr_inference():
+    code = """
+    if (a := 2) == 2:
+        a #@
+
+
+    # Test a function call
+    def test():
+        return 24
+
+    if (a := test()):
+        a #@
+
+    # Normal assignments in sequences
+    { (a:= 4) } #@
+    [ (a:= 5) ] #@
+
+    # Something more complicated
+    def test(value=(p := 24)): return p
+    [ y:= test()] #@
+
+    # Priority assignment
+    (x := 1, 2)
+    x #@
+    """
+    ast_nodes = extract_node(code)
+    node = next(ast_nodes[0].infer())
+    assert isinstance(node, nodes.Const)
+    assert node.value == 2
+
+    node = next(ast_nodes[1].infer())
+    assert isinstance(node, nodes.Const)
+    assert node.value == 24
+
+    node = next(ast_nodes[2].infer())
+    assert isinstance(node, nodes.Set)
+    assert isinstance(node.elts[0], nodes.Const)
+    assert node.elts[0].value == 4
+
+    node = next(ast_nodes[3].infer())
+    assert isinstance(node, nodes.List)
+    assert isinstance(node.elts[0], nodes.Const)
+    assert node.elts[0].value == 5
+
+    node = next(ast_nodes[4].infer())
+    assert isinstance(node, nodes.List)
+    assert isinstance(node.elts[0], nodes.Const)
+    assert node.elts[0].value == 24
+
+    node = next(ast_nodes[4].infer())
+    assert isinstance(node, nodes.Const)
+    assert node.value == 1
+
+
 if __name__ == "__main__":
     unittest.main()