Python: Port NonIteratorInForLoop.ql

Uses the `DuckTyping` module to approximate whether something is likely
to be an iterator or not.

We lose one test result due to the fact that we don't know what to do
about `for ... in 1` (because `1` is an instance of a built-in). I'm
going to defer addressing this until we get some modelling of built-in
types.

Author: tausbn

python/ql/src/Statements/NonIteratorInForLoop.ql

@@ -12,16 +12,15 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-from For loop, ControlFlowNodeWithPointsTo iter, Value v, ClassValue t, ControlFlowNode origin
+from For loop, Expr iter, Class cls
 where
-  loop.getIter().getAFlowNode() = iter and
-  iter.pointsTo(_, v, origin) and
-  v.getClass() = t and
-  not t.isIterable() and
-  not t.failedInference(_) and
-  not v = Value::named("None") and
-  not t.isDescriptorType()
-select loop, "This for-loop may attempt to iterate over a $@ of class $@.", origin,
-  "non-iterable instance", t, t.getName()
+  iter = loop.getIter() and
+  classInstanceTracker(cls).asExpr() = iter and
+  not DuckTyping::isIterable(cls) and
+  not DuckTyping::isDescriptor(cls) and
+  not (loop.isAsync() and DuckTyping::hasMethod(cls, "__aiter__")) and
+  not DuckTyping::hasUnresolvedBase(getADirectSuperclass*(cls))
+select loop, "This for-loop may attempt to iterate over a $@ of class $@.", iter,
+  "non-iterable instance", cls, cls.getName()

python/ql/test/3/query-tests/Statements/iter/NonIteratorInForLoop.expected

@@ -1,2 +1 @@
-| async_iterator.py:26:11:26:34 | For | This for-loop may attempt to iterate over a $@ of class $@. | async_iterator.py:26:20:26:33 | ControlFlowNode for MissingAiter() | non-iterable instance | async_iterator.py:13:1:13:19 | class MissingAiter | MissingAiter |
-| statements_test.py:34:5:34:19 | For | This for-loop may attempt to iterate over a $@ of class $@. | statements_test.py:34:18:34:18 | ControlFlowNode for IntegerLiteral | non-iterable instance | file://:0:0:0:0 | builtin-class int | int |
+| async_iterator.py:26:11:26:34 | For | This for-loop may attempt to iterate over a $@ of class $@. | async_iterator.py:26:20:26:33 | MissingAiter() | non-iterable instance | async_iterator.py:13:1:13:19 | Class MissingAiter | MissingAiter |

python/ql/test/query-tests/Statements/general/NonIteratorInForLoop.expected

@@ -1 +1 @@
-| test.py:50:1:50:23 | For | This for-loop may attempt to iterate over a $@ of class $@. | test.py:50:10:50:22 | ControlFlowNode for NonIterator() | non-iterable instance | test.py:45:1:45:26 | class NonIterator | NonIterator |
+| test.py:50:1:50:23 | For | This for-loop may attempt to iterate over a $@ of class $@. | test.py:50:10:50:22 | NonIterator() | non-iterable instance | test.py:45:1:45:26 | Class NonIterator | NonIterator |