Fix mutual static references between HttpMethod and HttpMethodImpl

src/main/java/io/vertx/core/http/HttpMethod.java

@@ -280,6 +280,6 @@ public interface HttpMethod {
    * @return an un-modifiable list of known HTTP methods
    */
   static List<HttpMethod> values() {
-    return HttpMethodImpl.ALL;
+    return HttpMethods.ALL;
   }
 }

src/main/java/io/vertx/core/http/HttpMethods.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2011-2019 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+ * which is available at https://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+ */
+package io.vertx.core.http;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * List of HTTP methods, this class is used to avoid exposing a modifiable field on {@link HttpMethod} and the
+ * {@link io.vertx.core.http.impl.HttpMethodImpl} implementation cannot statically define this field {@link HttpMethod}
+ * creates static {@link io.vertx.core.http.impl.HttpMethodImpl} instances.
+ *
+ * @author <a href="mailto:julien@julienviet.com">Julien Viet</a>
+ */
+class HttpMethods {
+
+  static final List<HttpMethod> ALL = Collections.unmodifiableList(Arrays.asList(
+    HttpMethod.OPTIONS,
+    HttpMethod.GET,
+    HttpMethod.HEAD,
+    HttpMethod.POST,
+    HttpMethod.PUT,
+    HttpMethod.DELETE,
+    HttpMethod.TRACE,
+    HttpMethod.CONNECT,
+    HttpMethod.PATCH,
+    HttpMethod.PROPFIND,
+    HttpMethod.PROPPATCH,
+    HttpMethod.MKCOL,
+    HttpMethod.COPY,
+    HttpMethod.MOVE,
+    HttpMethod.LOCK,
+    HttpMethod.UNLOCK,
+    HttpMethod.MKCALENDAR,
+    HttpMethod.VERSION_CONTROL,
+    HttpMethod.REPORT,
+    HttpMethod.CHECKIN,
+    HttpMethod.CHECKOUT,
+    HttpMethod.UNCHECKOUT,
+    HttpMethod.MKWORKSPACE,
+    HttpMethod.UPDATE,
+    HttpMethod.LABEL,
+    HttpMethod.MERGE,
+    HttpMethod.BASELINE_CONTROL,
+    HttpMethod.MKACTIVITY,
+    HttpMethod.ORDERPATCH,
+    HttpMethod.ACL,
+    HttpMethod.SEARCH
+  ));
+}

src/main/java/io/vertx/core/http/impl/HttpMethodImpl.java

@@ -19,40 +19,6 @@ import java.util.Objects;
 
 public class HttpMethodImpl implements HttpMethod {
 
-  public static final List<HttpMethod> ALL = Collections.unmodifiableList(Arrays.asList(
-    HttpMethod.OPTIONS,
-    HttpMethod.GET,
-    HttpMethod.HEAD,
-    HttpMethod.POST,
-    HttpMethod.PUT,
-    HttpMethod.DELETE,
-    HttpMethod.TRACE,
-    HttpMethod.CONNECT,
-    HttpMethod.PATCH,
-    HttpMethod.PROPFIND,
-    HttpMethod.PROPPATCH,
-    HttpMethod.MKCOL,
-    HttpMethod.COPY,
-    HttpMethod.MOVE,
-    HttpMethod.LOCK,
-    HttpMethod.UNLOCK,
-    HttpMethod.MKCALENDAR,
-    HttpMethod.VERSION_CONTROL,
-    HttpMethod.REPORT,
-    HttpMethod.CHECKIN,
-    HttpMethod.CHECKOUT,
-    HttpMethod.UNCHECKOUT,
-    HttpMethod.MKWORKSPACE,
-    HttpMethod.UPDATE,
-    HttpMethod.LABEL,
-    HttpMethod.MERGE,
-    HttpMethod.BASELINE_CONTROL,
-    HttpMethod.MKACTIVITY,
-    HttpMethod.ORDERPATCH,
-    HttpMethod.ACL,
-    HttpMethod.SEARCH
-  ));
-
   public static io.netty.handler.codec.http.HttpMethod toNetty(HttpMethod method) {
     if (method instanceof HttpMethodImpl) {
       return ((HttpMethodImpl) method).nettyMethod;

src/test/java/io/vertx/core/http/HttpMethodTest.java

@@ -11,12 +11,16 @@
 package io.vertx.core.http;
 
 import io.vertx.core.http.impl.HttpMethodImpl;
+import org.junit.Assert;
 import org.junit.Test;
 
 import java.util.Arrays;
+import java.util.List;
 
+import static junit.framework.TestCase.assertTrue;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.fail;
@@ -162,4 +166,11 @@ public class HttpMethodTest {
     assertEquals(HttpMethodImpl.toNetty(HttpMethod.valueOf("foo")).name(), "foo");
     assertEquals(HttpMethodImpl.fromNetty(io.netty.handler.codec.http.HttpMethod.valueOf("foo")).name(), "foo");
   }
+
+  @Test
+  public void testValues() {
+    List<HttpMethod> list = HttpMethod.values();
+    assertTrue(!list.isEmpty());
+    list.forEach(Assert::assertNotNull);
+  }
 }