QL: Add ql/missing-qldoc query.

ql/src/queries/style/docs/MissingQLDoc.ql

@@ -0,0 +1,25 @@
+/**
+ * @name Missing QLDoc.
+ * @description Library classes should have QLDoc.
+ * @kind problem
+ * @problem.severity recommendation
+ * @id ql/missing-qldoc
+ * @tags maintainability
+ * @precision high
+ */
+
+import ql
+
+from File f, Class c
+where
+  f = c.getLocation().getFile() and
+  not exists(c.getQLDoc()) and // no QLDoc
+  f.getExtension() = "qll" and // in a library
+  not c.isPrivate() and // class is public
+  not exists(Module m |
+    m.getAMember*() = c and
+    m.isPrivate() // modules containing the class are public
+  ) and
+  not exists(c.getAliasType()) and // class is not just an alias
+  not f.getParentContainer*().getBaseName().toLowerCase() = ["internal", "experimental", "test"] // exclusions
+select c, "This library class should have QLDoc."