Ruby: Add missing QL docs

ruby/ql/lib/codeql/ruby/DataFlow.qll

@@ -5,6 +5,10 @@
 
 import codeql.Locations
 
+/**
+ * Provides classes for performing local (intra-procedural) and
+ * global (inter-procedural) data flow analyses.
+ */
 module DataFlow {
   import codeql.ruby.dataflow.internal.DataFlowImpl
 }

ruby/ql/lib/codeql/ruby/ast/Erb.qll

@@ -37,6 +37,7 @@ class ErbTemplate extends TTemplate, ErbAstNode {
 
   final override string getAPrimaryQlClass() { result = "ErbTemplate" }
 
+  /** Gets a child node, if any. */
   ErbAstNode getAChildNode() { toGenerated(result) = g.getChild(_) }
 }
 

ruby/ql/lib/codeql/ruby/ast/Expr.qll

@@ -207,6 +207,7 @@ class BodyStmt extends StmtSequence, TBodyStmt {
     result = unique(Ensure s | toGenerated(s) = getBodyStmtChild(this, _))
   }
 
+  /** Holds if this block has an `ensure` block. */
   final predicate hasEnsure() { exists(this.getEnsure()) }
 
   override AstNode getAChild(string pred) {