Make igetattr() idempotent (#2208)

This addresses some reports of varying results when running pylint with ``--jobs.
The original inconsistency was due to a performance optimization in 2d7a87b for
a pathological case, but we have no source for the original bug report it targeted.

Author: jacobtylerwalls

ChangeLog

@@ -17,6 +17,12 @@ Release date: TBA
 
 * Reduce file system access in ``ast_from_file()``.
 
+* Make ``igetattr()`` idempotent. This addresses some reports of varying results
+  when running pylint with ``--jobs``.
+
+  Closes pylint-dev/pylint#4356
+  Refs #7
+
 * Fix incorrect cache keys for inference results, thereby correctly inferring types
   for calls instantiating types dynamically.
 

astroid/bases.py

@@ -277,14 +277,6 @@ def igetattr(
             context = InferenceContext()
         try:
             context.lookupname = name
-            # avoid recursively inferring the same attr on the same class
-            if context.push(self._proxied):
-                raise 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(

tests/test_inference.py

@@ -4024,7 +4024,7 @@ def __getitem__(self, name):
         flow['app']['config']['doffing'] = AttributeDict() #@
         """
         )
-        self.assertIsNone(helpers.safe_infer(ast_node.targets[0]))
+        self.assertIsInstance(helpers.safe_infer(ast_node.targets[0]), Instance)
 
     def test_classmethod_inferred_by_context(self) -> None:
         ast_node = extract_node(
@@ -6120,6 +6120,20 @@ def __exit__(self, ex_type, ex_value, ex_tb):
     next(node.infer())
 
 
+def test_igetattr_idempotent() -> None:
+    code = """
+    class InferMeTwice:
+        item = 10
+
+    InferMeTwice()
+    """
+    call = extract_node(code)
+    instance = call.inferred()[0]
+    context_to_be_used_twice = InferenceContext()
+    assert util.Uninferable not in instance.igetattr("item", context_to_be_used_twice)
+    assert util.Uninferable not in instance.igetattr("item", context_to_be_used_twice)
+
+
 def test_infer_context_manager_with_unknown_args() -> None:
     code = """
     class client_log(object):