Treat warnings as errors when compiling

See gh-21271

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

@@ -25,6 +25,7 @@ import java.util.function.Consumer;
 
 import io.spring.javaformat.gradle.FormatTask;
 import io.spring.javaformat.gradle.SpringJavaFormatPlugin;
+import org.gradle.api.JavaVersion;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.artifacts.ConfigurationContainer;
@@ -56,7 +57,13 @@ import org.springframework.boot.build.testing.TestFailuresPlugin;
  * <li>{@link Test} tasks are configured to use JUnit Platform and use a max heap of 1024M
  * <li>{@link JavaCompile}, {@link Javadoc}, and {@link FormatTask} tasks are configured
  * to use UTF-8 encoding
- * <li>{@link JavaCompile} tasks are configured to use {@code -parameters}
+ * <li>{@link JavaCompile} tasks are configured to use {@code -parameters} and, when
+ * compiling with Java 8, to:
+ * <ul>
+ * <li>Treat warnings as errors
+ * <li>Enable {@code unchecked}, {@code deprecation}, {@code rawtypes}, and {@code varags}
+ * warnings
+ * </ul>
  * <li>{@link Jar} tasks are configured to produce jars with LICENSE.txt and NOTICE.txt
  * files and the following manifest entries:
  * <ul>
@@ -149,6 +156,9 @@ class JavaConventions {
 			if (!args.contains("-parameters")) {
 				args.add("-parameters");
 			}
+			if (JavaVersion.current() == JavaVersion.VERSION_1_8) {
+				args.add("-Werror");
+			}
 		});
 	}
 

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/reactive/WebFluxTest.java

@@ -32,7 +32,6 @@ import org.springframework.boot.test.autoconfigure.core.AutoConfigureCache;
 import org.springframework.boot.test.autoconfigure.filter.TypeExcludeFilters;
 import org.springframework.boot.test.autoconfigure.json.AutoConfigureJson;
 import org.springframework.boot.test.context.SpringBootTest;
-import org.springframework.boot.test.mock.mockito.MockBean;
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.context.annotation.Import;
 import org.springframework.core.annotation.AliasFor;
@@ -55,9 +54,10 @@ import org.springframework.test.web.reactive.server.WebTestClient;
  * {@link WebTestClient}. For more fine-grained control of WebTestClient the
  * {@link AutoConfigureWebTestClient @AutoConfigureWebTestClient} annotation can be used.
  * <p>
- * Typically {@code @WebFluxTest} is used in combination with {@link MockBean @MockBean}
- * or {@link Import @Import} to create any collaborators required by your
- * {@code @Controller} beans.
+ * Typically {@code @WebFluxTest} is used in combination with
+ * {@link org.springframework.boot.test.mock.mockito.MockBean @MockBean} or
+ * {@link Import @Import} to create any collaborators required by your {@code @Controller}
+ * beans.
  * <p>
  * If you are looking to load your full application configuration and use WebTestClient,
  * you should consider {@link SpringBootTest @SpringBootTest} combined with

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/servlet/WebMvcTest.java

@@ -31,7 +31,6 @@ import org.springframework.boot.test.autoconfigure.OverrideAutoConfiguration;
 import org.springframework.boot.test.autoconfigure.core.AutoConfigureCache;
 import org.springframework.boot.test.autoconfigure.filter.TypeExcludeFilters;
 import org.springframework.boot.test.context.SpringBootTest;
-import org.springframework.boot.test.mock.mockito.MockBean;
 import org.springframework.context.annotation.ComponentScan.Filter;
 import org.springframework.context.annotation.Import;
 import org.springframework.core.annotation.AliasFor;
@@ -56,7 +55,8 @@ import org.springframework.test.web.servlet.MockMvc;
  * WebDriver). For more fine-grained control of MockMVC the
  * {@link AutoConfigureMockMvc @AutoConfigureMockMvc} annotation can be used.
  * <p>
- * Typically {@code @WebMvcTest} is used in combination with {@link MockBean @MockBean} or
+ * Typically {@code @WebMvcTest} is used in combination with
+ * {@link org.springframework.boot.test.mock.mockito.MockBean @MockBean} or
  * {@link Import @Import} to create any collaborators required by your {@code @Controller}
  * beans.
  * <p>

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/build.gradle

@@ -15,6 +15,7 @@ sourceSets {
 }
 
 dependencies {
+	testCompileOnly("com.google.code.findbugs:jsr305:3.0.2")
 	testImplementation(enforcedPlatform(project(":spring-boot-project:spring-boot-dependencies")))
 	testImplementation(project(":spring-boot-project:spring-boot-tools:spring-boot-test-support"))
 	testImplementation("javax.validation:validation-api")

spring-boot-project/spring-boot-tools/spring-boot-loader-tools/build.gradle

@@ -65,3 +65,9 @@ processResources {
 	dependsOn reproducibleLoaderJar
 	dependsOn reproducibleJarModeLayerToolsJar
 }
+
+compileJava {
+	if ((!project.hasProperty("buildJavaHome")) && JavaVersion.current() == JavaVersion.VERSION_1_8) {
+		options.compilerArgs += ['-Xlint:-sunapi', '-XDenableSunApiLintControl']	
+	}	
+}