C#: Add example of missing sink generation.

Author: michaelnebel

csharp/ql/test/utils/modelgenerator/dataflow/CaptureSinkModels.ext.yml

@@ -6,6 +6,13 @@ extensions:
       - [ "Sinks", "NewSinks", False, "Sink", "(System.Object)", "", "Argument[0]", "test-sink", "manual"]
       - [ "Sinks", "NewSinks", False, "Sink2", "(System.Object)", "", "Argument[0]", "test-sink2", "manual"]
       - [ "Sinks", "NewSinks", False, "ManualSinkAlreadyDefined", "(System.Object)", "", "Argument[0]", "test-sink", "manual"]
+      - [ "Sinks", "NewSinks", False, "SaveAndGet", "(System.Object)", "", "Argument[0]", "test-sink", "df-generated"]
+
+  - addsTo:
+      pack: codeql/csharp-all
+      extensible: sourceModel
+    data:
+      - [ "Sinks", "NewSinks", False, "SaveAndGet", "(System.Object)", "", "ReturnValue", "test-source", "manual"]
 
   - addsTo:
       pack: codeql/csharp-all

csharp/ql/test/utils/modelgenerator/dataflow/Sinks.cs

@@ -24,6 +24,15 @@ public class NewSinks
     // neutral=Sinks;NewSinks;NoSink;(System.Object);summary;df-generated
     public static void NoSink(object o) => throw null;
 
+    // Sink and Source defined in the extensible file next to the sink test.
+    // MISSING SINK
+    // neutral=Sinks;NewSinks;SaveAndGet;(System.Object);summary;df-generated
+    public static object SaveAndGet(object o)
+    {
+        Sink(o);
+        return null;
+    }
+
     // New sink
     // sink=Sinks;NewSinks;false;WrapResponseWrite;(System.Object);;Argument[0];html-injection;df-generated
     // neutral=Sinks;NewSinks;WrapResponseWrite;(System.Object);summary;df-generated