Add new experimental query MultipleArgumentsToSetConstructor.

javascript/ql/src/experimental/StandardLibrary/MultipleArgumentsToSetConstructor.ql

@@ -0,0 +1,22 @@
+/**
+ * @name Multiple arguments to `Set` constructor
+ * @description The `Set` constructor ignores all but the first argument, so passing multiple
+ *              arguments may indicate a mistake.
+ * @kind problem
+ * @problem.severity warning
+ * @precision high
+ * @id js/multiple-arguments-to-set-constructor
+ * @tags correctness
+ */
+
+import javascript
+
+from DataFlow::NewNode newSet, DataFlow::Node ignoredArg
+where
+  newSet = DataFlow::globalVarRef("Set").getAnInstantiation() and
+  (
+    ignoredArg = newSet.getArgument(any(int n | n > 0))
+    or
+    ignoredArg = newSet.getASpreadArgument()
+  )
+select ignoredArg, "All but the first argument to the Set constructor are ignored."