QL code and tests for C#/C++/JavaScript.

javascript/ql/src/external/DuplicateFunction.ql

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+/**
+ * @name Duplicate function
+ * @description There is another function that shares a lot of code with this function.
+ *              Extract the common parts to a shared utility function to improve maintainability.
+ * @kind problem
+ * @problem.severity recommendation
+ * @id js/duplicate-function
+ * @tags testability
+ *       useless-code
+ *       maintainability
+ *       statistical
+ *       non-attributable
+ *       duplicate-code
+ * @precision medium
+ */
+
+import javascript
+import CodeDuplication
+import semmle.javascript.RestrictedLocations
+
+from Function f, Function g, float percent
+where duplicateContainers(f, g, percent) and
+      f.getNumBodyStmt() > 5 and
+      not duplicateContainers(f.getEnclosingStmt().getContainer(), g.getEnclosingStmt().getContainer(), _)
+select (FirstLineOf)f, percent.floor() + "% of statements in " + f.describe() +
+       " are duplicated in $@.", (FirstLineOf)g, g.describe()