AST: add consistency query

ql/consistency-queries/AstConsistency.ql

@@ -0,0 +1,20 @@
+import codeql_ruby.AST
+
+private string getAPrimaryQlClass(AstNode node) {
+  result = node.getAPrimaryQlClass()
+  or
+  not exists(node.getAPrimaryQlClass()) and result = "(none)"
+}
+
+query predicate missingParent(AstNode node, string cls) {
+  not exists(node.getParent()) and
+  node.getLocation().getFile().getExtension() != "erb" and
+  not node instanceof Toplevel and
+  cls = getAPrimaryQlClass(node)
+}
+
+query predicate multipleParents(AstNode node, AstNode parent, string cls) {
+  parent = node.getParent() and
+  count(node.getParent()) > 1 and
+  cls = getAPrimaryQlClass(parent)
+}