--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/main/JavaCompiler.java	Mon Feb 06 11:11:43 2017 +0100
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/main/JavaCompiler.java	Mon Feb 06 18:14:51 2017 +0530
@@ -45,6 +45,7 @@
 import javax.tools.DiagnosticListener;
 import javax.tools.JavaFileManager;
 import javax.tools.JavaFileObject;
+import javax.tools.JavaFileObject.Kind;
 import javax.tools.StandardLocation;
 
 import com.sun.source.util.TaskEvent;
@@ -623,7 +624,8 @@
                 keepComments = true;
                 genEndPos = true;
             }
-            Parser parser = parserFactory.newParser(content, keepComments(), genEndPos, lineDebugInfo);
+            Parser parser = parserFactory.newParser(content, keepComments(), genEndPos,
+                                lineDebugInfo, filename.isNameCompatible("module-info", Kind.SOURCE));
             tree = parser.parseCompilationUnit();
             if (verbose) {
                 log.printVerbose("parsing.done", Long.toString(elapsed(msec)));

--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java	Mon Feb 06 11:11:43 2017 +0100
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java	Mon Feb 06 18:14:51 2017 +0530
@@ -70,6 +70,10 @@
      */
     private static final int infixPrecedenceLevels = 10;
 
+    /** Is the parser instantiated to parse a module-info file ?
+     */
+    private final boolean parseModuleInfo;
+
     /** The scanner used for lexical analysis.
      */
     protected Lexer S;
@@ -138,10 +142,21 @@
     /** Construct a parser from a given scanner, tree factory and log.
      */
     protected JavacParser(ParserFactory fac,
+                          Lexer S,
+                          boolean keepDocComments,
+                          boolean keepLineMap,
+                          boolean keepEndPositions) {
+        this(fac, S, keepDocComments, keepLineMap, keepEndPositions, false);
+
+    }
+    /** Construct a parser from a given scanner, tree factory and log.
+     */
+    protected JavacParser(ParserFactory fac,
                      Lexer S,
                      boolean keepDocComments,
                      boolean keepLineMap,
-                     boolean keepEndPositions) {
+                     boolean keepEndPositions,
+                     boolean parseModuleInfo) {
         this.S = S;
         nextToken(); // prime the pump
         this.F = fac.F;
@@ -165,6 +180,7 @@
         this.allowUnderscoreIdentifier = source.allowUnderscoreIdentifier();
         this.allowPrivateInterfaceMethods = source.allowPrivateInterfaceMethods();
         this.keepDocComments = keepDocComments;
+        this.parseModuleInfo = parseModuleInfo;
         docComments = newDocCommentTable(keepDocComments, fac);
         this.keepLineMap = keepLineMap;
         this.errorTree = F.Erroneous();
@@ -3347,8 +3363,13 @@
             } else {
                 errs = List.of(mods);
             }
-            return toP(F.Exec(syntaxError(pos, errs, "expected3",
-                                          CLASS, INTERFACE, ENUM)));
+            final JCErroneous erroneousTree;
+            if (parseModuleInfo) {
+                erroneousTree = syntaxError(pos, errs, "expected.module.or.open");
+            } else {
+                erroneousTree = syntaxError(pos, errs, "expected3", CLASS, INTERFACE, ENUM);
+            }
+            return toP(F.Exec(erroneousTree));
         }
     }
 

--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/parser/ParserFactory.java	Mon Feb 06 11:11:43 2017 +0100
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/parser/ParserFactory.java	Mon Feb 06 18:14:51 2017 +0530
@@ -81,7 +81,11 @@
     }
 
     public JavacParser newParser(CharSequence input, boolean keepDocComments, boolean keepEndPos, boolean keepLineMap) {
+        return newParser(input, keepDocComments, keepEndPos, keepLineMap, false);
+    }
+
+    public JavacParser newParser(CharSequence input, boolean keepDocComments, boolean keepEndPos, boolean keepLineMap, boolean parseModuleInfo) {
         Lexer lexer = scannerFactory.newScanner(input, keepDocComments);
-        return new JavacParser(this, lexer, keepDocComments, keepLineMap, keepEndPos);
+        return new JavacParser(this, lexer, keepDocComments, keepLineMap, keepEndPos, parseModuleInfo);
     }
 }

--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties	Mon Feb 06 11:11:43 2017 +0100
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties	Mon Feb 06 18:14:51 2017 +0530
@@ -1895,6 +1895,9 @@
 compiler.err.expected.module=\
     ''module'' expected
 
+compiler.err.expected.module.or.open=\
+    ''module'' or ''open'' expected
+
 compiler.err.dot.class.expected=\
     ''.class'' expected
 

--- a/langtools/src/jdk.jshell/share/classes/jdk/jshell/ReplParserFactory.java	Mon Feb 06 11:11:43 2017 +0100
+++ b/langtools/src/jdk.jshell/share/classes/jdk/jshell/ReplParserFactory.java	Mon Feb 06 18:14:51 2017 +0530
@@ -56,4 +56,9 @@
         com.sun.tools.javac.parser.Lexer lexer = scannerFactory.newScanner(input, keepDocComments);
         return new ReplParser(this, lexer, keepDocComments, keepLineMap, keepEndPos);
     }
+
+    @Override
+    public JavacParser newParser(CharSequence input, boolean keepDocComments, boolean keepEndPos, boolean keepLineMap, boolean parseModuleInfo) {
+        return newParser(input, keepDocComments, keepEndPos, keepLineMap);
+    }
 }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/diags/examples/UnexpectedTokenInModuleInfo/module-info.java	Mon Feb 06 18:14:51 2017 +0530
@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2017, 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.
+ */
+
+// key: compiler.err.expected.module.or.open
+
+weak module m {}
\ No newline at end of file

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/modules/UnexpectedTokenInModuleInfoTest.java	Mon Feb 06 18:14:51 2017 +0530
@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2017, 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 8166420
+ * @summary Confusing error message when reading bad module declaration
+ * @library /tools/lib
+ * @modules
+ *      jdk.compiler/com.sun.tools.javac.api
+ *      jdk.compiler/com.sun.tools.javac.main
+ * @build toolbox.ToolBox toolbox.JavacTask ModuleTestBase
+ * @run main UnexpectedTokenInModuleInfoTest
+ */
+
+import java.nio.file.*;
+import java.util.List;
+import java.util.Arrays;
+
+import toolbox.JavacTask;
+import toolbox.Task;
+
+public class UnexpectedTokenInModuleInfoTest extends ModuleTestBase {
+    public static void main(String... args) throws Exception {
+        UnexpectedTokenInModuleInfoTest t = new UnexpectedTokenInModuleInfoTest();
+        t.runTests();
+    }
+
+    @Test
+    public void testSingleModule(Path base) throws Exception {
+        Path src = base.resolve("src");
+        tb.writeFile(src.resolve("module-info.java"), "weak module m { }");
+
+         List<String> output = new JavacTask(tb)
+            .options("-XDrawDiagnostics")
+            .files(src.resolve("module-info.java"))
+            .run(Task.Expect.FAIL)
+            .writeAll()
+            .getOutputLines(Task.OutputKind.DIRECT);
+
+         List<String> expected = Arrays.asList("module-info.java:1:1: compiler.err.expected.module.or.open",
+                "1 error");
+        if (!output.containsAll(expected)) {
+            throw new Exception("Expected output not found");
+        }
+    }
+}
\ No newline at end of file

--- a/langtools/test/tools/javac/parser/extend/TrialParserFactory.java	Mon Feb 06 11:11:43 2017 +0100
+++ b/langtools/test/tools/javac/parser/extend/TrialParserFactory.java	Mon Feb 06 18:14:51 2017 +0530
@@ -52,4 +52,9 @@
         com.sun.tools.javac.parser.Lexer lexer = scannerFactory.newScanner(input, keepDocComments);
         return new TrialParser(this, lexer, keepDocComments, keepLineMap, keepEndPos);
     }
+
+    @Override
+    public JavacParser newParser(CharSequence input, boolean keepDocComments, boolean keepEndPos, boolean keepLineMap, boolean parseModuleInfo) {
+        return newParser(input, keepDocComments, keepEndPos, keepLineMap);
+    }
 }