Allow annotated assign with attrs

ChangeLog

@@ -16,6 +16,10 @@ Release Date: TBA
   attributes, but rather virtual ones, thus an operation such as `getattr()`
   does not make sense for them.
 
+* Update attr brain to partly understand annotated attributes
+
+  Close #656
+
 
 What's New in astroid 2.3.0?
 ============================

astroid/brain/brain_attrs.py

@@ -37,21 +37,27 @@ def attr_attributes_transform(node):
     node.locals["__attrs_attrs__"] = [astroid.Unknown(parent=node)]
 
     for cdefbodynode in node.body:
-        if not isinstance(cdefbodynode, astroid.Assign):
+        if not isinstance(cdefbodynode, (astroid.Assign, astroid.AnnAssign)):
             continue
         if isinstance(cdefbodynode.value, astroid.Call):
             if cdefbodynode.value.func.as_string() not in ATTRIB_NAMES:
                 continue
         else:
             continue
-        for target in cdefbodynode.targets:
+        targets = (
+            cdefbodynode.targets
+            if hasattr(cdefbodynode, "targets")
+            else [cdefbodynode.target]
+        )
+        for target in targets:
 
             rhs_node = astroid.Unknown(
                 lineno=cdefbodynode.lineno,
                 col_offset=cdefbodynode.col_offset,
                 parent=cdefbodynode,
             )
             node.locals[target.name] = [rhs_node]
+            node.instance_attrs[target.name] = [rhs_node]
 
 
 MANAGER.register_transform(

astroid/tests/unittest_brain.py

@@ -1187,6 +1187,19 @@ class Foo:
         """
         next(astroid.extract_node(code).infer())
 
+    @test_utils.require_version(minver="3.6")
+    def test_attrs_with_annotation(self):
+        code = """
+        import attr
+
+        @attr.s
+        class Foo:
+            bar: int = attr.ib(default=5)
+        Foo()
+        """
+        should_be_unknown = next(astroid.extract_node(code).infer()).getattr("bar")[0]
+        self.assertIsInstance(should_be_unknown, astroid.Unknown)
+
 
 class RandomSampleTest(unittest.TestCase):
     def test_inferred_successfully(self):