--- /dev/null	2018-12-18 21:39:03.000000000 +0530
+++ new/src/jdk.jextract/share/classes/com/sun/tools/jextract/DuplicateDeclarationHandler.java	2018-12-18 21:39:03.000000000 +0530
@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.sun.tools.jextract;
+
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import com.sun.tools.jextract.parser.Parser;
+import com.sun.tools.jextract.tree.EnumTree;
+import com.sun.tools.jextract.tree.HeaderTree;
+import com.sun.tools.jextract.tree.SimpleTreeVisitor;
+import com.sun.tools.jextract.tree.StructTree;
+import com.sun.tools.jextract.tree.Tree;
+import com.sun.tools.jextract.tree.TreeMaker;
+import com.sun.tools.jextract.tree.TreePhase;
+import com.sun.tools.jextract.tree.TreePrinter;
+import jdk.internal.clang.Cursor;
+import jdk.internal.clang.SourceLocation;
+
+/**
+ * Removes redundant declarations.
+ */
+final class DuplicateDeclarationHandler extends SimpleTreeVisitor<Void, Void>
+        implements TreePhase {
+    private final TreeMaker treeMaker = new TreeMaker();
+
+    // Potential Tree instances that will go into transformed HeaderTree
+    // are collected in this list.
+    private List<Tree> decls = new ArrayList<>();
+
+    // declarations seen already
+    private final Map<String, Tree> declarationsSeen = new HashMap<>();
+    private void saveDeclaration(Tree t) {
+        if (!t.name().isEmpty()) {
+            declarationsSeen.put(t.name(), t);
+        }
+    }
+
+    @Override
+    public HeaderTree transform(HeaderTree ht) {
+        // Process all header declarations are collect potential
+        // declarations that will go into transformed HeaderTree
+        // into the this.decls field.
+        ht.accept(this, null);
+
+        return treeMaker.createHeader(ht.cursor(), ht.path(), decls);
+    }
+
+    @Override
+    public Void defaultAction(Tree tree, Void v) {
+        if (!declarationsSeen.containsKey(tree.name())) {
+            decls.add(tree);
+        }
+        return null;
+    }
+
+    @Override
+    public Void visitEnum(EnumTree e, Void v) {
+        defaultAction(e, v);
+        if (!e.isDefinition()) {
+            saveDeclaration(e); 
+        }
+        return null;
+    }
+
+    @Override
+    public Void visitHeader(HeaderTree ht, Void v) {
+        ht.declarations().forEach(decl -> decl.accept(this, null));
+        return null;
+    }
+
+    @Override
+    public Void visitStruct(StructTree s, Void v) {
+        defaultAction(s, v);
+        if (!s.isDefinition()) {
+            saveDeclaration(s); 
+        }
+        return null;
+    }
+
+    // test main to manually check this visitor
+    public static void main(String[] args) {
+        if (args.length == 0) {
+            System.err.println("Expected a header file");
+            return;
+        }
+
+        Context context = new Context();
+        Parser p = new Parser(context, true);
+        List<Path> paths = Arrays.stream(args).map(Paths::get).collect(Collectors.toList());
+        Path builtinInc = Paths.get(System.getProperty("java.home"), "conf", "jextract");
+        List<String> clangArgs = List.of("-I" + builtinInc);
+        List<HeaderTree> headers = p.parse(paths, clangArgs);
+        TreePrinter printer = new TreePrinter();
+        DuplicateDeclarationHandler handler = new DuplicateDeclarationHandler();
+        for (HeaderTree ht : headers) {
+            handler.transform(ht).accept(printer, null);
+        }
+    }
+}