QL: add query detecting fields that are only used within the charpred

Author: erik-krogh

ql/ql/src/queries/style/FieldOnlyUsedInCharPred.ql

@@ -0,0 +1,20 @@
+/**
+ * @name Field only used in CharPred
+ * @description A field only being used in the charpred suggests that the field should be inlined into the charpred.
+ * @kind problem
+ * @problem.severity recommendation
+ * @id ql/field-only-used-in-charpred
+ * @tags maintainability
+ * @precision very-high
+ */
+
+import ql
+
+from Class c, FieldDecl f
+where
+  c.getAField() = f and
+  forex(FieldAccess access | access.getDeclaration() = f.getVarDecl() |
+    access.getEnclosingPredicate() = c.getCharPred()
+  ) and
+  not f.getVarDecl().overrides(_)
+select f, "Field is only used in CharPred"