fix default method gets wrapped twice (#641)

* fix default method gets wrapped twice

* check if default method only once

hystrix/src/main/java/feign/hystrix/HystrixInvocationHandler.java

@@ -26,6 +26,7 @@ import java.util.Set;
 
 import feign.InvocationHandlerFactory.MethodHandler;
 import feign.Target;
+import feign.Util;
 import rx.Completable;
 import rx.Observable;
 import rx.Single;
@@ -143,7 +144,9 @@ final class HystrixInvocationHandler implements InvocationHandler {
       }
     };
 
-    if (isReturnsHystrixCommand(method)) {
+    if (Util.isDefault(method)) {
+      return hystrixCommand.execute();
+    } else if (isReturnsHystrixCommand(method)) {
       return hystrixCommand;
     } else if (isReturnsObservable(method)) {
       // Create a cold Observable

hystrix/src/test/java/feign/hystrix/HystrixBuilderTest.java

@@ -51,6 +51,18 @@ public class HystrixBuilderTest {
   @Rule
   public final MockWebServer server = new MockWebServer();
 
+  @Test
+  public void defaultMethodReturningHystrixCommand() {
+    server.enqueue(new MockResponse().setBody("\"foo\""));
+
+    TestInterface api = target();
+
+    HystrixCommand<String> command = api.defaultMethodReturningCommand();
+
+    assertThat(command).isNotNull();
+    assertThat(command.execute()).isEqualTo("foo");
+  }
+
   @Test
   public void hystrixCommand() {
     server.enqueue(new MockResponse().setBody("\"foo\""));
@@ -606,6 +618,10 @@ public class HystrixBuilderTest {
     @Headers("Accept: application/json")
     HystrixCommand<String> command();
 
+    default HystrixCommand<String> defaultMethodReturningCommand() {
+      return command();
+    }
+
     @RequestLine("GET /")
     @Headers("Accept: application/json")
     HystrixCommand<Integer> intCommand();