Python: just use ListElementContent for iterables

Author: yoff

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPrivate.qll

@@ -179,33 +179,10 @@ private predicate synthDictSplatArgumentNodeStoreStep(
  * data from `x.name` is stored into the `yield` (and can subsequently be read out of the iterable).
  */
 predicate yieldStoreStep(Node nodeFrom, Content c, Node nodeTo) {
-  exists(Yield yield, Function func |
+  exists(Yield yield |
     nodeTo.asCfgNode() = yield.getAFlowNode() and
     nodeFrom.asCfgNode() = yield.getValue().getAFlowNode() and
-    func.containsInScope(yield)
-  |
-    exists(Comp comp | func = comp.getFunction() |
-      (
-        comp instanceof ListComp or
-        comp instanceof GeneratorExp
-      ) and
-      c instanceof ListElementContent
-      or
-      comp instanceof SetComp and
-      c instanceof SetElementContent
-      or
-      comp instanceof DictComp and
-      c instanceof DictionaryElementAnyContent
-    )
-    or
-    not exists(Comp comp | func = comp.getFunction()) and
-    (
-      c instanceof ListElementContent
-      or
-      c instanceof SetElementContent
-      or
-      c instanceof DictionaryElementAnyContent
-    )
+    c instanceof ListElementContent
   )
 }
 

python/ql/lib/semmle/python/frameworks/Stdlib.qll

@@ -4224,6 +4224,10 @@ module StdlibPrivate {
         preservesValue = true
       )
       or
+      input = "Argument[0].ListElement.TupleElement[1]" and
+      output = "ReturnValue.DictionaryElementAny" and
+      preservesValue = true
+      or
       exists(DataFlow::DictionaryElementContent dc, string key | key = dc.getKey() |
         input = "Argument[" + key + ":]" and
         output = "ReturnValue.DictionaryElement[" + key + "]" and

python/ql/test/library-tests/dataflow/coverage/test_builtins.py

@@ -132,8 +132,8 @@ def test_dict_from_keyword():
 @expects(2)
 def test_dict_from_list():
     d = dict([("k", SOURCE), ("k1", NONSOURCE)])
-    SINK(d["k"]) #$ MISSING: flow="SOURCE, l:-1 -> d[k]"
-    SINK_F(d["k1"])
+    SINK(d["k"]) #$ flow="SOURCE, l:-1 -> d['k']"
+    SINK_F(d["k1"]) #$ SPURIOUS: flow="SOURCE, l:-2 -> d['k1']"  // due to imprecise list content
 
 @expects(2)
 def test_dict_from_dict():