Enable varargs compilation warnings

See gh-21271

buildSrc/src/main/java/org/springframework/boot/build/JavaConventions.java

@@ -157,7 +157,8 @@ class JavaConventions {
 				args.add("-parameters");
 			}
 			if (JavaVersion.current() == JavaVersion.VERSION_1_8) {
-				args.addAll(Arrays.asList("-Werror", "-Xlint:unchecked", "-Xlint:deprecation", "-Xlint:rawtypes"));
+				args.addAll(Arrays.asList("-Werror", "-Xlint:unchecked", "-Xlint:deprecation", "-Xlint:rawtypes",
+						"-Xlint:varargs"));
 			}
 		});
 	}

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/web/server/ManagementWebServerFactoryCustomizer.java

@@ -49,6 +49,7 @@ public abstract class ManagementWebServerFactoryCustomizer<T extends Configurabl
 	private final Class<? extends WebServerFactoryCustomizer<?>>[] customizerClasses;
 
 	@SafeVarargs
+	@SuppressWarnings("varargs")
 	protected ManagementWebServerFactoryCustomizer(ListableBeanFactory beanFactory,
 			Class<? extends WebServerFactoryCustomizer<?>>... customizerClasses) {
 		this.beanFactory = beanFactory;

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/session/NonUniqueSessionRepositoryFailureAnalyzerTests.java

@@ -49,6 +49,7 @@ class NonUniqueSessionRepositoryFailureAnalyzerTests {
 	}
 
 	@SafeVarargs
+	@SuppressWarnings("varargs")
 	private final Exception createFailure(Class<? extends SessionRepository<?>>... candidates) {
 		return new NonUniqueSessionRepositoryException(Arrays.asList(candidates));
 	}

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/context/FilteredClassLoader.java

@@ -77,6 +77,7 @@ public class FilteredClassLoader extends URLClassLoader {
 	 * name of a class or a resource name.
 	 */
 	@SafeVarargs
+	@SuppressWarnings("varargs")
 	public FilteredClassLoader(Predicate<String>... filters) {
 		this(Arrays.asList(filters), Arrays.asList(filters));
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/ServletContextInitializerBeans.java

@@ -77,6 +77,7 @@ public class ServletContextInitializerBeans extends AbstractCollection<ServletCo
 	private List<ServletContextInitializer> sortedList;
 
 	@SafeVarargs
+	@SuppressWarnings("varargs")
 	public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
 			Class<? extends ServletContextInitializer>... initializerTypes) {
 		this.initializers = new LinkedMultiValueMap<>();