Infer args unpacking of ``self``

Certain stdlib modules use ``*args`` to encapsulate
the ``self`` parameter, which results in uninferable
instances given we rely on the presence of the ``self``
argument to figure out the instance where we should be
setting attributes.

Close PyCQA/pylint#3216

3 files changed, 32 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 3cae14b5..ba37918c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,16 @@ Release Date: TBA
 
 * Allow inferring positional only arguments.
 
+* Infer args unpacking of ``self``
+
+  Certain stdlib modules use ``*args`` to encapsulate
+  the ``self`` parameter, which results in uninferable
+  instances given we rely on the presence of the ``self``
+  argument to figure out the instance where we should be
+  setting attributes.
+
+  Close PyCQA/pylint#3216
+
 
 What's New in astroid 2.3.2?
 ============================
diff --git a/astroid/protocols.py b/astroid/protocols.py
index 8b682e48..84e3571b 100644
--- a/astroid/protocols.py
+++ b/astroid/protocols.py
@@ -339,6 +339,9 @@ def _arguments_infer_argname(self, name, context):
     if name == self.vararg:
         vararg = nodes.const_factory(())
         vararg.parent = self
+        if not self.arguments and self.parent.name == "__init__":
+            cls = self.parent.parent.scope()
+            vararg.elts = [bases.Instance(cls)]
         yield vararg
         return
     if name == self.kwarg:
diff --git a/tests/unittest_inference.py b/tests/unittest_inference.py
index a2ad7e6d..9ce0c8d2 100644
--- a/tests/unittest_inference.py
+++ b/tests/unittest_inference.py
@@ -5319,5 +5319,24 @@ def test_posonlyargs_inference():
     assert inferred.type == "method"
 
 
+def test_infer_args_unpacking_of_self():
+    code = """
+    class A:
+        def __init__(*args, **kwargs):
+            self, *args = args
+            self.data = {1: 2}
+            self #@
+    A().data #@
+    """
+    self, data = extract_node(code)
+    inferred_self = next(self.infer())
+    assert isinstance(inferred_self, Instance)
+    assert inferred_self.name == "A"
+
+    inferred_data = next(data.infer())
+    assert isinstance(inferred_data, nodes.Dict)
+    assert inferred_data.as_string() == "{1: 2}"
+
+
 if __name__ == "__main__":
     unittest.main()