C#: Make positional pattern read step.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll

@@ -563,13 +563,19 @@ module LocalFlow {
     exists(IsExpr e |
       e1 = e.getExpr() and
       e2 = e.getPattern() and
-      e2 instanceof TuplePatternExpr
+      (
+        e2 instanceof TuplePatternExpr or
+        e2 instanceof RecursivePatternExpr
+      )
     )
     or
     exists(Switch sw |
       e1 = sw.getExpr() and
       e2 = sw.getACase().getPattern() and
-      e2 instanceof TuplePatternExpr
+      (
+        e2 instanceof TuplePatternExpr or
+        e2 instanceof RecursivePatternExpr
+      )
     )
   }
 
@@ -823,7 +829,8 @@ private predicate fieldOrPropertyStore(ContentSet c, Expr src, Expr q, boolean p
       te = q and
       src = te.getArgument(pragma[only_bind_into](i)) and
       te.isConstruction() and
-      f = q.getType().(TupleType).getElement(pragma[only_bind_into](i)) and
+      // TODO: Should this be unBoundDeclaration() as well - otherwise it is not symmetric with the readStep?
+      f = q.getType().(TupleType).getElement(pragma[only_bind_into](i)).getUnboundDeclaration() and
       postUpdate = false
     )
   )
@@ -2208,6 +2215,23 @@ predicate storeStep(Node node1, ContentSet c, Node node2) {
   storeStepDelegateCall(node1, c, node2)
 }
 
+private predicate readStepPattern(Node node1, Content c, Node node2) {
+  exists(RecursivePatternExpr parent, PatternExpr child, int i |
+    node1.asExpr() = parent and
+    child = parent.getPositionalPatterns().getPattern(i) and
+    c.(FieldContent).getField() = parent.getType().(TupleType).getElement(i).getUnboundDeclaration()
+  |
+    child = node2.asExpr().(RecursivePatternExpr)
+    or
+    child = node2.asExpr().(TuplePatternExpr)
+    or
+    exists(AssignableDefinitions::PatternDefinition lvd |
+      node2.(AssignableDefinitionNode).getDefinition() = lvd and
+      child = lvd.getDeclaration()
+    )
+  )
+}
+
 private predicate readContentStep(Node node1, Content c, Node node2) {
   arrayRead(node1.asExpr(), node2.asExpr()) and
   c instanceof ElementContent
@@ -2255,6 +2279,8 @@ private predicate readContentStep(Node node1, Content c, Node node2) {
     )
   )
   or
+  readStepPattern(node1, c, node2)
+  or
   VariableCapture::readStep(node1, c, node2)
 }