add ql/counting-to-zero

Author: erik-krogh

ql/ql/src/queries/style/CountingToZero.ql

@@ -0,0 +1,21 @@
+/**
+ * @name Counting zero elements
+ * @description Use not exists instead of checking that there is zero elements in a set.
+ * @kind problem
+ * @problem.severity warning
+ * @id ql/counting-to-zero
+ * @precision high
+ */
+
+import ql
+
+from ComparisonFormula comp, int c, string msg
+where
+  c = 0 and // [0, 1] and // skipping the 1 case for now, as it seems too noisy.
+  comp.getOperator() = ["=", "!="] and
+  comp.getAnOperand().(Integer).getValue() = c and
+  comp.getAnOperand().(Aggregate).getKind() = ["count", "strictcount"] and
+  if c = 0
+  then msg = "Use not exists(..) instead of checking that there is zero elements in a set."
+  else msg = "Use unique(.. | |) instead of checking that there is one element in a set."
+select comp, msg