Python: Include all assignments in data flow paths

Like Ruby did in #12566

Author: RasmusWL

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

@@ -513,15 +513,10 @@ class CastNode extends Node {
  * explanations.
  */
 predicate neverSkipInPathGraph(Node n) {
-  // We include read- and store steps here to force them to be
-  // shown in path explanations.
-  // This hack is necessary, because we have included some of these
-  // steps as default taint steps, making them be suppressed in path
-  // explanations.
-  // We should revert this once, we can remove this steps from the
-  // default taint steps; this should be possible once we have
-  // implemented flow summaries and recursive content.
-  readStep(_, _, n) or storeStep(_, _, n)
+  exists(DefinitionNode def |
+    // ensure that all variable assignments are included in the path graph
+    def.getValue() = n.asCfgNode()
+  )
 }
 
 /**

python/ql/test/experimental/dataflow/path-graph/test.py

@@ -1,14 +1,14 @@
 def assign():
     x = SOURCE # $ path-node
 
-    y = x
+    y = x # $ path-node
 
     SINK(y) # $ path-node
 
 
     z = ""
 
-    z += x
+    z += x # $ path-node
 
     SINK(z) # $ path-node
 
@@ -18,7 +18,7 @@ class X: pass
     x = X()
     x.attr = SOURCE # $ path-node
 
-    y = x
+    y = x # $ path-node
 
     SINK(y.attr) # $ path-node