JS: Add test for SourceNode not depending on flowsTo

Author: asgerf

javascript/ql/test/library-tests/RecursionPrevention/SourceNodeFlowsTo.expected

@@ -0,0 +1 @@
+| Success |

javascript/ql/test/library-tests/RecursionPrevention/SourceNodeFlowsTo.ql

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+/**
+ * Test that fails to compile if the domain of `SourceNode` depends on `SourceNode.flowsTo` (recursively).
+ *
+ * This tests adds a negative dependency `flowsTo --!--> SourceNode`
+ * so that the undesired edge `SourceNode --> flowsTo` completes a negative cycle.
+ */
+import javascript
+
+class BadSourceNode extends DataFlow::SourceNode {
+  BadSourceNode() {
+    this.(DataFlow::PropRead).getPropertyName() = "foo"
+  }
+
+  override predicate flowsTo(DataFlow::Node node) {
+    not node instanceof DataFlow::SourceNode
+  }
+}
+
+select "Success"

javascript/ql/test/library-tests/RecursionPrevention/tst.js

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+// The contents of this file don't matter
+let x = 1;