--- a/langtools/src/share/classes/com/sun/tools/javac/code/Lint.java	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/code/Lint.java	Tue Dec 07 14:13:25 2010 -0800
@@ -134,6 +134,11 @@
         CAST("cast"),
 
         /**
+         * Warn about issues related to classfile contents
+         */
+        CLASSFILE("classfile"),
+
+        /**
          * Warn about use of deprecated items.
          */
         DEPRECATION("deprecation"),

--- a/langtools/src/share/classes/com/sun/tools/javac/jvm/ClassReader.java	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/jvm/ClassReader.java	Tue Dec 07 14:13:25 2010 -0800
@@ -32,6 +32,7 @@
 import java.util.Arrays;
 import java.util.EnumSet;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 import javax.lang.model.SourceVersion;
@@ -44,11 +45,13 @@
 
 import com.sun.tools.javac.comp.Annotate;
 import com.sun.tools.javac.code.*;
+import com.sun.tools.javac.code.Lint.LintCategory;
 import com.sun.tools.javac.code.Type.*;
 import com.sun.tools.javac.code.Symbol.*;
 import com.sun.tools.javac.code.Symtab;
 import com.sun.tools.javac.file.BaseFileObject;
 import com.sun.tools.javac.util.*;
+import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 
 import static com.sun.tools.javac.code.Flags.*;
 import static com.sun.tools.javac.code.Kinds.*;
@@ -102,6 +105,10 @@
      */
     boolean allowAnnotations;
 
+    /** Lint option: warn about classfile issues
+     */
+    boolean lintClassfile;
+
     /** Switch: preserve parameter names from the variable table.
      */
     public boolean saveParameterNames;
@@ -207,6 +214,11 @@
      */
     boolean haveParameterNameIndices;
 
+    /**
+     * The set of attribute names for which warnings have been generated for the current class
+     */
+    Set<Name> warnedAttrs = new HashSet<Name>();
+
     /** Get the ClassReader instance for this invocation. */
     public static ClassReader instance(Context context) {
         ClassReader instance = context.get(classReaderKey);
@@ -279,6 +291,8 @@
         typevars = new Scope(syms.noSymbol);
         debugJSR308 = options.isSet("TA:reader");
 
+        lintClassfile = Lint.instance(context).isEnabled(LintCategory.CLASSFILE);
+
         initAttributeReaders();
     }
 
@@ -870,7 +884,22 @@
         }
 
         boolean accepts(AttributeKind kind) {
-            return kinds.contains(kind) && majorVersion >= version.major;
+            if (kinds.contains(kind)) {
+                if (majorVersion > version.major || (majorVersion == version.major && minorVersion >= version.minor))
+                    return true;
+
+                if (lintClassfile && !warnedAttrs.contains(name)) {
+                    JavaFileObject prev = log.useSource(currentClassFile);
+                    try {
+                        log.warning(LintCategory.CLASSFILE, (DiagnosticPosition) null, "future.attr",
+                                name, version.major, version.minor, majorVersion, minorVersion);
+                    } finally {
+                        log.useSource(prev);
+                    }
+                    warnedAttrs.add(name);
+                }
+            }
+            return false;
         }
 
         abstract void read(Symbol sym, int attrLen);
@@ -889,7 +918,7 @@
 
     protected Map<Name, AttributeReader> attributeReaders = new HashMap<Name, AttributeReader>();
 
-    protected void initAttributeReaders() {
+    private void initAttributeReaders() {
         AttributeReader[] readers = {
             // v45.3 attributes
 
@@ -1561,7 +1590,7 @@
         public void accept(Visitor v) { ((ProxyVisitor)v).visitCompoundAnnotationProxy(this); }
         @Override
         public String toString() {
-            StringBuffer buf = new StringBuffer();
+            StringBuilder buf = new StringBuilder();
             buf.append("@");
             buf.append(type.tsym.getQualifiedName());
             buf.append("/*proxy*/{");
@@ -2286,6 +2315,7 @@
             throw new CompletionFailure(c, "user-selected completion failure by class name");
         }
         currentOwner = c;
+        warnedAttrs.clear();
         JavaFileObject classfile = c.classfile;
         if (classfile != null) {
             JavaFileObject previousClassFile = currentClassFile;

--- a/langtools/src/share/classes/com/sun/tools/javac/resources/compiler.properties	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/resources/compiler.properties	Tue Dec 07 14:13:25 2010 -0800
@@ -767,6 +767,9 @@
 compiler.warn.source.no.bootclasspath=\
     bootstrap class path not set in conjunction with -source {0}
 
+compiler.warn.future.attr=\
+    {0} attribute introduced in version {1}.{2} class files is ignored in version {3}.{4} class files
+
 # Warnings related to annotation processing
 compiler.warn.proc.package.does.not.exist=\
     package {0} does not exist

--- a/langtools/src/share/classes/com/sun/tools/javac/util/RawDiagnosticFormatter.java	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/util/RawDiagnosticFormatter.java	Tue Dec 07 14:13:25 2010 -0800
@@ -27,6 +27,7 @@
 import java.util.Collection;
 import java.util.EnumSet;
 import java.util.Locale;
+import javax.tools.JavaFileObject;
 
 import com.sun.tools.javac.api.DiagnosticFormatter.Configuration.*;
 import com.sun.tools.javac.api.Formattable;
@@ -62,7 +63,7 @@
     //provide common default formats
     public String formatDiagnostic(JCDiagnostic d, Locale l) {
         try {
-            StringBuffer buf = new StringBuffer();
+            StringBuilder buf = new StringBuilder();
             if (d.getPosition() != Position.NOPOS) {
                 buf.append(formatSource(d, false, null));
                 buf.append(':');
@@ -71,16 +72,22 @@
                 buf.append(formatPosition(d, COLUMN, null));
                 buf.append(':');
             }
+            else if (d.getSource() != null && d.getSource().getKind() == JavaFileObject.Kind.CLASS) {
+                buf.append(formatSource(d, false, null));
+                buf.append(":-:-:");
+            }
             else
                 buf.append('-');
             buf.append(' ');
             buf.append(formatMessage(d, null));
-            if (displaySource(d))
-                buf.append("\n" + formatSourceLine(d, 0));
+            if (displaySource(d)) {
+                buf.append("\n");
+                buf.append(formatSourceLine(d, 0));
+            }
             return buf.toString();
         }
         catch (Exception e) {
-            e.printStackTrace();
+            //e.printStackTrace();
             return null;
         }
     }
@@ -96,7 +103,9 @@
                 buf.append(",{");
                 for (String sub : formatSubdiagnostics(d, null)) {
                     buf.append(sep);
-                    buf.append("(" + sub + ")");
+                    buf.append("(");
+                    buf.append(sub);
+                    buf.append(")");
                     sep = ",";
                 }
                 buf.append('}');

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/T6999210.java	Tue Dec 07 14:13:25 2010 -0800
@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) 2010, 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.
+ */
+
+/*
+ * @test
+ * @bug 6999210
+ * @summary javac should be able to warn of anomalous conditions in classfiles
+ */
+
+import java.io.*;
+import java.util.*;
+
+public class T6999210 {
+    public static void main(String... args) throws Exception {
+        new T6999210().run();
+    }
+
+    void run() throws Exception {
+        File srcDir = new File("src");
+        File classesDir = new File("classes");
+        classesDir.mkdirs();
+
+        File c_java = writeFile(srcDir, "C.java", "class C<T> { }");
+        compile("-d", classesDir.getPath(), c_java.getPath());
+        File c_class = new File(classesDir, "C.class");
+        setMajorVersion(c_class, 48);
+        File d_java = writeFile(srcDir, "D.java", "class D { C c; }");
+
+        // verify no warning if -Xlint:classfile not enabled
+        String out1 = compile(
+            "-d", classesDir.getPath(),
+            "-classpath", classesDir.getPath(),
+            d_java.getPath());
+        if (out1.length() > 0)
+            error("unexpected output from javac");
+
+        // sanity check of warning when -XDrawDiagnostics not used
+        String out2 = compile(
+            "-d", classesDir.getPath(),
+            "-classpath", classesDir.getPath(),
+            "-Xlint:classfile",
+            d_java.getPath());
+        if (!out2.contains("[classfile]"))
+            error("expected output \"[classfile]\" not found");
+
+        // check specific details, using -XDrawDiagnostics
+        String out3 = compile(
+            "-d", classesDir.getPath(),
+            "-classpath", classesDir.getPath(),
+            "-Xlint:classfile", "-XDrawDiagnostics",
+            d_java.getPath());
+        String expect = "C.class:-:-: compiler.warn.future.attr: Signature, 49, 0, 48, 0";
+        if (!out3.contains(expect))
+            error("expected output \"" + expect + "\" not found");
+
+        if (errors > 0)
+            throw new Exception(errors + " errors occurred");
+    }
+
+    String compile(String... args) throws Exception {
+        System.err.println("compile: " + Arrays.asList(args));
+        StringWriter sw = new StringWriter();
+        PrintWriter pw = new PrintWriter(sw);
+        int rc = com.sun.tools.javac.Main.compile(args, pw);
+        pw.close();
+        String out = sw.toString();
+        if (out.length() > 0)
+            System.err.println(out);
+        if (rc != 0)
+            throw new Exception("compilation failed, rc=" + rc);
+        return out;
+    }
+
+    void setMajorVersion(File f, int major) throws IOException {
+        int len = (int) f.length();
+        byte[] data = new byte[len];
+        try (DataInputStream in = new DataInputStream(new FileInputStream(f))) {
+            in.readFully(data);
+        }
+        // u4 magic
+        // u2 minor
+        data[6] = (byte) (major >> 8);
+        data[7] = (byte) (major & 0xff);
+        try (FileOutputStream out = new FileOutputStream(f)) {
+            out.write(data);
+        }
+    }
+
+    File writeFile(File dir, String path, String body) throws IOException {
+        File f = new File(dir, path);
+        f.getParentFile().mkdirs();
+        try (FileWriter out = new FileWriter(f)) {
+            out.write(body);
+        }
+        return f;
+    }
+
+    void error(String msg) {
+        System.err.println("Error: " + msg);
+        errors++;
+    }
+
+    int errors;
+}

--- a/langtools/test/tools/javac/annotations/6214965/T6214965.out	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/test/tools/javac/annotations/6214965/T6214965.out	Tue Dec 07 14:13:25 2010 -0800
@@ -1,2 +1,2 @@
-- compiler.warn.annotation.method.not.found: CompilerAnnotationTest2, name2
+CompilerAnnotationTest.class:-:-: compiler.warn.annotation.method.not.found: CompilerAnnotationTest2, name2
 1 warning

--- a/langtools/test/tools/javac/annotations/6365854/test1.out	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/test/tools/javac/annotations/6365854/test1.out	Tue Dec 07 14:13:25 2010 -0800
@@ -1,2 +1,2 @@
-- compiler.warn.annotation.method.not.found.reason: test.annotation.TestAnnotation, test, (compiler.misc.class.file.not.found: test.annotation.TestAnnotation)
+TestCore.class:-:-: compiler.warn.annotation.method.not.found.reason: test.annotation.TestAnnotation, test, (compiler.misc.class.file.not.found: test.annotation.TestAnnotation)
 1 warning

--- a/langtools/test/tools/javac/annotations/6365854/test2.out	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/test/tools/javac/annotations/6365854/test2.out	Tue Dec 07 14:13:25 2010 -0800
@@ -1,2 +1,2 @@
-- compiler.warn.annotation.method.not.found: test.annotation.TestAnnotation, test
+TestCore.class:-:-: compiler.warn.annotation.method.not.found: test.annotation.TestAnnotation, test
 1 warning

--- a/langtools/test/tools/javac/diags/examples.not-yet.txt	Mon Dec 06 11:51:02 2010 +0000
+++ b/langtools/test/tools/javac/diags/examples.not-yet.txt	Tue Dec 07 14:13:25 2010 -0800
@@ -104,6 +104,7 @@
 compiler.warn.annotation.method.not.found               # ClassReader
 compiler.warn.annotation.method.not.found.reason        # ClassReader
 compiler.warn.big.major.version                         # ClassReader
+compiler.warn.future.attr                               # ClassReader
 compiler.warn.illegal.char.for.encoding
 compiler.warn.invalid.archive.file
 compiler.warn.override.bridge