PY-20832 Fixed: __iter__ is not inferred from for-statement

Update PyNamedParameterImpl.collectUsedAttributes to honour for-statements

python/src/com/jetbrains/python/psi/impl/PyNamedParameterImpl.java

@@ -361,6 +361,18 @@ public class PyNamedParameterImpl extends PyBaseElementImpl<PyNamedParameterStub
 
           super.visitPyCallExpression(node);
         }
+
+        @Override
+        public void visitPyForStatement(PyForStatement node) {
+          Optional
+            .of(node.getForPart())
+            .map(PyForPart::getSource)
+            .map(PyExpression::getReference)
+            .filter(reference -> reference.isReferenceTo(PyNamedParameterImpl.this))
+            .ifPresent(reference -> result.add(PyNames.ITER));
+
+          super.visitPyForStatement(node);
+        }
       });
     }
     return result;

python/testData/inspections/PyAugmentAssignmentInspection/sequenceConcatenation.py

@@ -19,16 +19,15 @@ def expand(values1, values2):
     <weak_warning descr="Assignment can be replaced with augmented assignment">values1 = values1 + values2</weak_warning>
 
 
-#def expand(values1, values2):
-#    for a in values1:
-#      print(a)
-#
-#    for b in values2:
-#      print(b)
-#
-#    values1 = values2 + values1
-#    values1 = values1 + values2
-#    inspection should suggest replacement only for the second assignment
+def expand(values1, values2):
+    for a in values1:
+      print(a)
+
+    for b in values2:
+      print(b)
+
+    values1 = values2 + values1
+    <weak_warning descr="Assignment can be replaced with augmented assignment">values1 = values1 + values2</weak_warning>
 
 
 def expand(values1, values2):

python/testSrc/com/jetbrains/python/PyTypeTest.java

@@ -1145,6 +1145,15 @@ public class PyTypeTest extends PyTestCase {
            "expr = f\n");
   }
 
+  // PY-20832
+  public void testStructuralTypeWithDunderIter() {
+    doTest("{__iter__}",
+           "def expand(values1):\n" +
+           "    for a in values1:\n" +
+           "        print(a)\n" +
+           "    expr = values1\n");
+  }
+
   // PY-20833
   public void testStructuralTypeWithDunderLen() {
     doTest("{__len__}",