--- a/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/IndexRedirectWriter.java	Tue Jan 15 10:40:32 2019 -0800
+++ b/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/IndexRedirectWriter.java	Tue Jan 15 11:05:25 2019 -0800
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2019, 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
@@ -40,6 +40,8 @@
 import jdk.javadoc.internal.doclets.toolkit.util.DocPath;
 import jdk.javadoc.internal.doclets.toolkit.util.DocPaths;
 
+import java.util.Collections;
+
 /**
  * Writes a file that tries to redirect to an alternate page.
  * The redirect uses JavaScript, if enabled, falling back on

--- a/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/util/Extern.java	Tue Jan 15 10:40:32 2019 -0800
+++ b/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/util/Extern.java	Tue Jan 15 11:05:25 2019 -0800
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2019, 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
@@ -45,6 +45,8 @@
 import javax.tools.Diagnostic.Kind;
 import javax.tools.DocumentationTool;
 
+import com.sun.tools.javac.code.Flags;
+import com.sun.tools.javac.code.Symbol.ModuleSymbol;
 import jdk.javadoc.doclet.Reporter;
 import jdk.javadoc.internal.doclets.toolkit.BaseConfiguration;
 import jdk.javadoc.internal.doclets.toolkit.Resources;
@@ -276,6 +278,12 @@
             ModuleElement moduleElement = utils.containingModule(packageElement);
             Map<String, Item> pkgMap = packageItems.get(utils.getModuleName(moduleElement));
             item = (pkgMap != null) ? pkgMap.get(utils.getPackageName(packageElement)) : null;
+            if (item == null && isAutomaticModule(moduleElement)) {
+                pkgMap = packageItems.get(utils.getModuleName(null));
+                if (pkgMap != null) {
+                    item = pkgMap.get(utils.getPackageName(packageElement));
+                }
+            }
         }
         return item;
     }
@@ -420,12 +428,25 @@
                             path), null);
                 }
             } else if (moduleName == null) {
-                throw new Fault(resources.getText("doclet.linkMismatch_ModuleLinkedtoPackage",
-                        path), null);
+                // suppress the error message in the case of automatic modules
+                if (!isAutomaticModule(me)) {
+                    throw new Fault(resources.getText("doclet.linkMismatch_ModuleLinkedtoPackage",
+                            path), null);
+                }
             }
         }
     }
 
+    // The following should be replaced by a new method such as Elements.isAutomaticModule
+    private boolean isAutomaticModule(ModuleElement me) {
+        if (me == null) {
+            return false;
+        } else {
+            ModuleSymbol msym = (ModuleSymbol) me;
+            return (msym.flags() & Flags.AUTOMATIC_MODULE) != 0;
+        }
+    }
+
     public boolean isUrl (String urlCandidate) {
         try {
             new URL(urlCandidate);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/langtools/jdk/javadoc/doclet/testLinkOption/TestLinkOptionWithAutomaticModule.java	Tue Jan 15 11:05:25 2019 -0800
@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2019, 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 8212233
+ * @summary The code being documented uses modules but the packages defined in $URL are in the unnamed module.
+ * @library /tools/lib ../lib
+ * @modules
+ *      jdk.javadoc/jdk.javadoc.internal.tool
+ *      jdk.compiler/com.sun.tools.javac.api
+ *      jdk.compiler/com.sun.tools.javac.main
+ * @build JavadocTester toolbox.JarTask toolbox.JavacTask toolbox.ModuleBuilder toolbox.ToolBox
+ * @run main TestLinkOptionWithAutomaticModule
+ */
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import toolbox.JarTask;
+import toolbox.JavacTask;
+import toolbox.ModuleBuilder;
+import toolbox.ToolBox;
+
+public class TestLinkOptionWithAutomaticModule extends JavadocTester {
+
+    public static void main(String... args) throws Exception {
+        TestLinkOptionWithAutomaticModule tester = new TestLinkOptionWithAutomaticModule();
+        tester.runTests(m -> new Object[]{ Path.of(m.getName()) });
+    }
+
+    final ToolBox tb = new ToolBox();
+    private Path libJar;
+    private Path libAPI;
+
+    TestLinkOptionWithAutomaticModule() throws IOException {
+        initLib();
+    }
+
+    private void initLib() throws IOException {
+        // create library: write source, compile it, jar it
+        Path lib = Path.of("lib");
+        Path libSrc = lib.resolve("src");
+        tb.writeJavaFiles(libSrc, "package lib; public class LibClass { }");
+        Path libClasses = Files.createDirectories(lib.resolve("classes"));
+
+        new JavacTask(tb)
+                .outdir(libClasses)
+                .files(tb.findJavaFiles(libSrc))
+                .run()
+                .writeAll();
+
+        libJar = lib.resolve("MyLib.jar");
+        new JarTask(tb, libJar)
+                .baseDir(libClasses)
+                .files(".")
+                .run();
+
+        libAPI = lib.resolve("api");
+        javadoc("-d", libAPI.toString(),
+                "-sourcepath", libSrc.toString(),
+                "lib");
+        checkExit(Exit.OK);
+    }
+
+    @Test
+    public void testLinkUnnamedToAutomaticModule(Path base) throws IOException {
+
+        // create API referring to library
+        Path src = base.resolve("src");
+        tb.writeJavaFiles(src, "package p; public class MyClass extends lib.LibClass { }");
+
+        // run javadoc with library as automatic module
+        Path api = base.resolve("api");
+        javadoc("-d", api.toString(),
+                "-sourcepath", src.toString(),
+                "--add-modules", "MyLib",
+                "--module-path", libJar.toString(),
+                "-linkoffline", "http://myWebsite", libAPI.toAbsolutePath().toString(),
+                "p");
+        checkExit(Exit.OK);
+        checkOutput("p/MyClass.html", true,
+                "extends <a href=\"http://myWebsite/lib/LibClass.html?is-external=true\" "
+                + "title=\"class or interface in lib\" class=\"externalLink\">LibClass</a>");
+    }
+
+    @Test
+    public void testLinkNamedToAutomaticModule(Path base) throws IOException {
+
+        // create API referring to library
+        Path src = base.resolve("src");
+        new ModuleBuilder(tb, "my.module")
+                .exports("p")
+                .requires("MyLib")
+                .classes("package p; public class MyClass extends lib.LibClass { }")
+                .write(src);
+
+        // run javadoc with library as automatic module
+        Path api = base.resolve("api");
+        javadoc("-d", api.toString(),
+                "--module-source-path", src.toString(),
+                "--module-path", libJar.toString(),
+                "-linkoffline", "http://myWebsite", libAPI.toAbsolutePath().toString(),
+                "--module", "my.module");
+        checkExit(Exit.OK);
+        checkOutput("my.module/p/MyClass.html", true,
+                "extends <a href=\"http://myWebsite/lib/LibClass.html?is-external=true\" "
+                + "title=\"class or interface in lib\" class=\"externalLink\">LibClass</a>");
+    }
+
+    @Test
+    public void testLinkNamedToUnnamedModule(Path base) throws IOException {
+
+        // create API referring to library
+        Path src = base.resolve("src");
+        new ModuleBuilder(tb, "my.module")
+                .exports("p")
+                .classes("package p; public class MyClass extends lib.LibClass { }")
+                .write(src);
+
+        // run javadoc with library as unnamed module
+        Path api = base.resolve("api");
+        javadoc("-d", api.toString(),
+                "--module-source-path", src.toString(),
+                "--add-reads", "my.module=ALL-UNNAMED",
+                "--class-path", libJar.toString(),
+                "-linkoffline", "http://myWebsite", libAPI.toAbsolutePath().toString(),
+                "--module", "my.module");
+        checkExit(Exit.OK);
+        checkOutput("my.module/p/MyClass.html", true,
+                "extends <a href=\"http://myWebsite/lib/LibClass.html?is-external=true\" "
+                + "title=\"class or interface in lib\" class=\"externalLink\">LibClass</a>");
+    }
+}