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
+      )
     )
   }
 
@@ -2208,6 +2214,24 @@ predicate storeStep(Node node1, ContentSet c, Node node2) {
   storeStepDelegateCall(node1, c, node2)
 }
 
+private predicate readStepPattern(Node node1, Content c, Node node2) {
+  exists(RecursivePatternExpr pattern, PatternExpr item, int i |
+    node1.asExpr() = pattern and
+    item = pattern.getPositionalPatterns().getPattern(i) and
+    c.(FieldContent).getField() =
+      pattern.getType().(TupleType).getElement(i).getUnboundDeclaration()
+  |
+    item = node2.asExpr().(RecursivePatternExpr)
+    or
+    item = node2.asExpr().(TuplePatternExpr)
+    or
+    exists(AssignableDefinitions::PatternDefinition lvd |
+      node2.(AssignableDefinitionNode).getDefinition() = lvd and
+      item = 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)
 }