--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/util/RichDiagnosticFormatter.java	Fri Aug 24 13:23:39 2018 -0700
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/util/RichDiagnosticFormatter.java	Fri Aug 24 13:30:56 2018 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2009, 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
@@ -539,7 +539,13 @@
             }
             nameSimplifier.addUsage(t.tsym);
             visit(t.getTypeArguments());
-            if (t.getEnclosingType() != Type.noType)
+            Type enclosingType;
+            try {
+                enclosingType = t.getEnclosingType();
+            } catch (CompletionFailure cf) {
+                return null;
+            }
+            if (enclosingType != Type.noType)
                 visit(t.getEnclosingType());
             return null;
         }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/langtools/tools/javac/T8209173/CodeCompletionExceptTest.java	Fri Aug 24 13:30:56 2018 -0700
@@ -0,0 +1,100 @@
+/*
+ * 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.
+ */
+
+/*
+ * @test
+ * @bug 8209173
+ * @summary javac fails with completion exception while reporting an error
+ * @library /tools/lib
+ * @modules jdk.jdeps/com.sun.tools.classfile
+ *          jdk.compiler/com.sun.tools.javac.api
+ *          jdk.compiler/com.sun.tools.javac.main
+ *          jdk.compiler/com.sun.tools.javac.util
+ *          jdk.jdeps/com.sun.tools.javap
+ * @build toolbox.ToolBox toolbox.JavacTask
+ * @run main CodeCompletionExceptTest
+ */
+
+import java.io.File;
+
+import toolbox.JavacTask;
+import toolbox.Task;
+import toolbox.ToolBox;
+
+public class CodeCompletionExceptTest {
+    private static final String MyListSource =
+            "import java.util.List;\n" +
+            "public interface MyList<E> extends List<E> {}";
+
+    private static final String C1Source =
+            "public class C1 {\n" +
+            "    int m(MyList<Integer> list) {\n" +
+            "        return 0;\n" +
+            "    }\n" +
+            "}";
+
+    private static final String C2Source =
+            "class C2 {\n" +
+            "    void m() {\n" +
+            "        (new C1()).m(1, 2, 3);\n" +
+            "    }\n" +
+            "}";
+
+    public static void main(String[] args) throws Exception {
+        new CodeCompletionExceptTest().run();
+    }
+
+    ToolBox tb = new ToolBox();
+
+    void run() throws Exception {
+        // first we compile MyList
+        new JavacTask(tb)
+                .sources(MyListSource)
+                .run();
+
+        // then with MyList.class in the cp we compile C1
+        new JavacTask(tb)
+                .sources(C1Source)
+                .classpath(System.getProperty("user.dir"))
+                .run();
+        // now we delete MyList.class
+        tb.deleteFiles(System.getProperty("user.dir") + File.separatorChar + "MyList.class");
+        /** and try to compile C2 which uses C1 which uses MyList but, MyList won't be in the
+         *  classpath so its symbol can't be completed while javac is generating the diagnostic error
+         *  the compiler should capture the completion exception and still be able to produce an error
+         *  message without crashing
+         */
+        String javacOut = new JavacTask(tb)
+                .sources(C2Source)
+                .classpath(System.getProperty("user.dir"))
+                .options("-XDrawDiagnostics")
+                .run(Task.Expect.FAIL)
+                .writeAll()
+                .getOutput(Task.OutputKind.DIRECT);
+        String expectedOuput =
+                "C2.java:3:19: compiler.err.cant.apply.symbol: kindname.method, m, MyList<java.lang.Integer>, int,int,int, kindname.class, C1, (compiler.misc.arg.length.mismatch)";
+        if (!javacOut.contains(expectedOuput)) {
+            throw new Exception("test failed, unexpected output");
+        }
+    }
+}