--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java	Tue Mar 14 08:19:41 2017 +0100
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java	Tue Mar 14 10:51:19 2017 +0100
@@ -714,6 +714,11 @@
         return rootModules.contains(module);
     }
 
+    public Set<ModuleSymbol> getRootModules() {
+        Assert.checkNonNull(rootModules);
+        return rootModules;
+    }
+
     class ModuleVisitor extends JCTree.Visitor {
         private ModuleSymbol sym;
         private final Set<ModuleSymbol> allRequires = new HashSet<>();