Fixes problems caused by @CheckReturnValue (#1310)

Allow return value of fail* methods to be ignored with CanIgnoreReturnValue annotation.

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

@@ -94,6 +94,7 @@
 import org.assertj.core.presentation.Representation;
 import org.assertj.core.presentation.StandardRepresentation;
 import org.assertj.core.presentation.UnicodeRepresentation;
+import org.assertj.core.util.CanIgnoreReturnValue;
 import org.assertj.core.util.CheckReturnValue;
 import org.assertj.core.util.Files;
 import org.assertj.core.util.URLs;
@@ -1331,6 +1332,7 @@ public static void setRemoveAssertJRelatedElementsFromStackTrace(boolean removeA
    * @return nothing, it's just to be used in doSomething(optional.orElse(() -> fail("boom")));.
    * @throws AssertionError with the given message.
    */
+  @CanIgnoreReturnValue
   public static <T> T fail(String failureMessage) {
     return Fail.fail(failureMessage);
   }
@@ -1344,6 +1346,7 @@ public static <T> T fail(String failureMessage) {
    * @return nothing, it's just to be used in doSomething(optional.orElse(() -&gt; fail("b%s", ""oom)));.
    * @throws AssertionError with the given built message.
    */
+  @CanIgnoreReturnValue
   public static <T> T fail(String failureMessage, Object... args) {
     return Fail.fail(failureMessage, args);
   }
@@ -1356,6 +1359,7 @@ public static <T> T fail(String failureMessage, Object... args) {
    * @return nothing, it's just to be used in doSomething(optional.orElse(() -&gt; fail("boom", cause)));.
    * @throws AssertionError with the given message and with the {@link Throwable} that caused the failure.
    */
+  @CanIgnoreReturnValue
   public static <T> T fail(String failureMessage, Throwable realCause) {
     return Fail.fail(failureMessage, realCause);
   }
@@ -1373,6 +1377,7 @@ public static <T> T fail(String failureMessage, Throwable realCause) {
    *           not been.
    *
    */
+  @CanIgnoreReturnValue
   public static <T> T failBecauseExceptionWasNotThrown(Class<? extends Throwable> throwableClass) {
     return Fail.shouldHaveThrown(throwableClass);
   }
@@ -1386,6 +1391,7 @@ public static <T> T failBecauseExceptionWasNotThrown(Class<? extends Throwable>
    * @throws AssertionError with a message explaining that a {@link Throwable} of given class was expected to be thrown but had
    *           not been.
    */
+  @CanIgnoreReturnValue
   public static <T> T shouldHaveThrown(Class<? extends Throwable> throwableClass) {
     return Fail.shouldHaveThrown(throwableClass);
   }

src/main/java/org/assertj/core/util/CanIgnoreReturnValue.java

@@ -0,0 +1,31 @@
+/*
+ * 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.util;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation to skip "CheckReturnValue" check.
+ */
+@Target({
+  ElementType.CONSTRUCTOR,
+  ElementType.METHOD,
+  ElementType.PACKAGE,
+  ElementType.TYPE,
+})
+@Retention(RetentionPolicy.CLASS)
+public @interface CanIgnoreReturnValue {
+}