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

cpp/ql/src/Likely Bugs/NestedLoopSameVar.ql

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+/**
+ * @name Nested loops with same variable
+ * @description When a nested loop uses the same iteration variable as its outer loop, the
+ *   behavior of the outer loop easily becomes difficult to understand as the
+ *   inner loop will affect its control flow. It is likely to be a typo.
+ * @kind problem
+ * @problem.severity warning
+ * @precision medium
+ * @id cpp/nested-loops-with-same-variable
+ * @tags maintainability
+ *       correctness
+ */
+import NestedLoopSameVar
+
+from ForStmt inner, Variable iteration, ForStmt outer
+where nestedForViolation(inner, iteration, outer)
+select inner.getCondition(), "Nested for statement uses loop variable $@ of enclosing $@.", iteration, iteration.getName(), outer, "for statement"