C#: Add dataflow field test for ref structs with ref and ordinary fields.

Author: michaelnebel

csharp/ql/test/library-tests/dataflow/fields/E.cs

@@ -17,7 +17,7 @@ static void NotASetter(S s, object o)
         s.Field = o;
     }
 
-    private void M()
+    private void M1()
     {
         var o = Source<object>(1);
         var s = CreateS(o);
@@ -28,6 +28,35 @@ private void M()
         Sink(s.Field); // no flow
     }
 
+    ref struct RefS
+    {
+        public object Field;
+        public ref object RefField;
+
+        public RefS(object o1, ref object o2)
+        {
+            Field = o1;
+            RefField = ref o2;
+        }
+    }
+
+    static void PartialSetter(RefS s, object o)
+    {
+        s.Field = o;
+        s.RefField = o;
+    }
+
+    private void M2()
+    {
+        var o1 = new object();
+        var o2 = new object();
+        var refs = new RefS(o1, ref o2);
+        var taint = Source<object>(2);
+        PartialSetter(refs, taint);
+        Sink(refs.Field); // no flow
+        Sink(refs.RefField); // $ hasValueFlow=2
+    }
+
     public static void Sink(object o) { }
 
     static T Source<T>(object source) => throw null;

csharp/ql/test/library-tests/dataflow/fields/FieldFlow.expected

@@ -1,4 +1,5 @@
 testFailures
+| E.cs:57:30:57:48 | // ... | Missing result:hasValueFlow=2 |
 edges
 | A.cs:5:17:5:28 | call to method Source<C> : C | A.cs:6:24:6:24 | access to local variable c : C |
 | A.cs:5:17:5:28 | call to method Source<C> : C | A.cs:6:24:6:24 | access to local variable c : C |