Java: Generalize data-flow library in preparation for C# adoption

Author: hvitved

java/ql/src/semmle/code/java/dataflow/internal/DataFlowDispatch.qll

@@ -1,6 +1,21 @@
 private import java
+private import DataFlowPrivate
 import semmle.code.java.dispatch.VirtualDispatch
 
+/**
+ * A return position. A return position describes how a value can return
+ * from a given callable. For Java, this is simply a method return.
+ */
+class ReturnPosition extends Method {
+  ReturnPosition() { exists(ReturnNode ret | ret.getEnclosingCallable() = this) }
+
+  /** Gets the callable that a value can be returned from. */
+  Method getCallable() { result = this }
+
+  /** Gets a return node that can return a value at this position. */
+  ReturnNode getAReturnNode() { result.getEnclosingCallable() = this }
+}
+
 cached
 private module DispatchImpl {
   /**
@@ -186,5 +201,17 @@ private module DispatchImpl {
     result = viableImplInCallContext(ma, ctx) and
     reducedViableImplInReturn(result, ma)
   }
+
+  /**
+   * Gets a node that can read the value returned at position `pos` for the
+   * call `call`.
+   */
+  cached
+  OutNode getAnOutputAtCall(DataFlowCall call, ReturnPosition pos) {
+    exists(Method m | pos.getCallable() = m |
+      m = viableCallable(call) and
+      result = call.getNode()
+    )
+  }
 }
 import DispatchImpl