Move assertThat(CompletionStage<RESULT> actual) from AssertionsForCla…

…ssTypes to AssertionsForInterfaceTypes.

Fixes #839.

src/main/java/org/assertj/core/api/Assertions.java

@@ -212,7 +212,7 @@ public static <RESULT> CompletableFutureAssert<RESULT> assertThat(CompletableFut
    */
   @CheckReturnValue
   public static <RESULT> CompletableFutureAssert<RESULT> assertThat(CompletionStage<RESULT> actual) {
-    return AssertionsForClassTypes.assertThat(actual);
+    return AssertionsForInterfaceTypes.assertThat(actual);
   }
 
   /**

src/main/java/org/assertj/core/api/AssertionsForClassTypes.java

@@ -36,7 +36,6 @@
 import java.util.OptionalInt;
 import java.util.OptionalLong;
 import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.CompletionStage;
 
 import org.assertj.core.api.ThrowableAssert.ThrowingCallable;
 import org.assertj.core.api.exception.RuntimeIOException;
@@ -85,21 +84,6 @@ public static <RESULT> CompletableFutureAssert<RESULT> assertThat(CompletableFut
     return new CompletableFutureAssert<>(actual);
   }
 
-  /**
-   * Create assertion for {@link java.util.concurrent.CompletionStage} by converting it to a {@link CompletableFuture} and returning a {@link CompletableFutureAssert}.
-   * <p>
-   * If the given {@link java.util.concurrent.CompletionStage} is null, the {@link CompletableFuture} in the returned {@link CompletableFutureAssert} will also be null.
-   *
-   * @param actual the actual value.
-   * @param <RESULT> the type of the value contained in the {@link java.util.concurrent.CompletionStage}.
-   *
-   * @return the created assertion object.
-   */
-  @CheckReturnValue
-  public static <RESULT> CompletableFutureAssert<RESULT> assertThat(CompletionStage<RESULT> actual) {
-    return new CompletableFutureAssert<>(actual);
-  }
-
   /**
    * Create assertion for {@link java.util.Optional}.
    *

src/main/java/org/assertj/core/api/AssertionsForInterfaceTypes.java

@@ -16,6 +16,8 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
 import java.util.function.DoublePredicate;
 import java.util.function.IntPredicate;
 import java.util.function.LongPredicate;
@@ -378,5 +380,20 @@ public static DoublePredicateAssert assertThat(DoublePredicate actual) {
     return new DoublePredicateAssert(actual);
   }
 
+  /**
+   * Create assertion for {@link java.util.concurrent.CompletionStage} by converting it to a {@link CompletableFuture} and returning a {@link CompletableFutureAssert}.
+   * <p>
+   * If the given {@link java.util.concurrent.CompletionStage} is null, the {@link CompletableFuture} in the returned {@link CompletableFutureAssert} will also be null.
+   *
+   * @param actual the actual value.
+   * @param <RESULT> the type of the value contained in the {@link java.util.concurrent.CompletionStage}.
+   *
+   * @return the created assertion object.
+   */
+  @CheckReturnValue
+  public static <RESULT> CompletableFutureAssert<RESULT> assertThat(CompletionStage<RESULT> actual) {
+    return new CompletableFutureAssert<>(actual);
+  }
+
 
 }

src/test/java/org/assertj/core/api/Assertions_avoid_ambiguous_reference_compilation_error_Test.java

@@ -0,0 +1,34 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ *
+ * Copyright 2012-2018 the original author or authors.
+ */
+package org.assertj.core.api;
+
+import org.junit.Test;
+
+import java.util.Date;
+
+public class Assertions_avoid_ambiguous_reference_compilation_error_Test {
+
+  @Test
+  public void should_not_report_ambiguous_reference_compilation_error() {
+    // does not compile, explanation: https://stackoverflow.com/questions/29499847/ambiguous-method-in-java-8-why
+    // Assertions.assertThat(getDate()).isEqualTo(getDate());
+
+    // compiles since AssertionsForClassTypes does not provide assertThat for interfaces   
+    AssertionsForClassTypes.assertThat(getDate()).isEqualTo(getDate());
+  }
+
+  protected static <T extends Date> T getDate() {
+    return (T) new Date(123);
+  }
+
+}