Fix problems with auto-configuration architecture checks

Closes gh-48216

buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureRules.java

@@ -421,6 +421,8 @@ final class ArchitectureRules {
 		return ArchRuleDefinition.members()
 			.that()
 			.areDeclaredInClassesThat(areRegularAutoConfiguration())
+			.and()
+			.areDeclaredInClassesThat(areNotKotlinClasses())
 			.and(areNotDefaultConstructors())
 			.and(areNotConstants())
 			.and(dontOverridePublicMethods())
@@ -440,13 +442,18 @@ final class ArchitectureRules {
 	}
 
 	static DescribedPredicate<JavaClass> areRegularAutoConfiguration() {
-		return DescribedPredicate.describe("Regular @AutoConfiguration",
+		return DescribedPredicate.describe("are regular @AutoConfiguration",
 				(javaClass) -> javaClass.isAnnotatedWith(AUTOCONFIGURATION_ANNOTATION)
 						&& !javaClass.getName().contains("TestAutoConfiguration") && !javaClass.isAnnotation());
 	}
 
+	static DescribedPredicate<JavaClass> areNotKotlinClasses() {
+		return DescribedPredicate.describe("are not Kotlin classes",
+				(javaClass) -> !javaClass.isAnnotatedWith("kotlin.Metadata"));
+	}
+
 	static DescribedPredicate<JavaClass> areTestAutoConfiguration() {
-		return DescribedPredicate.describe("Test @AutoConfiguration",
+		return DescribedPredicate.describe("are test @AutoConfiguration",
 				(javaClass) -> javaClass.isAnnotatedWith(AUTOCONFIGURATION_ANNOTATION)
 						&& javaClass.getName().contains("TestAutoConfiguration") && !javaClass.isAnnotation());
 	}

buildSrc/src/main/java/org/springframework/boot/build/architecture/AutoConfigurationChecker.java

@@ -31,12 +31,16 @@ import org.springframework.util.ReflectionUtils;
 /**
  * Finds all configurations from auto-configurations (either nested configurations or
  * imported ones) and checks that these classes don't contain public members.
+ * <p>
+ * Kotlin classes are ignored as Kotlin does not have package-private visibility and
+ * {@code internal} isn't a good substitute.
  *
  * @author Moritz Halbritter
  */
 class AutoConfigurationChecker {
 
-	private final DescribedPredicate<JavaClass> isAutoConfiguration = ArchitectureRules.areRegularAutoConfiguration();
+	private final DescribedPredicate<JavaClass> isAutoConfiguration = ArchitectureRules.areRegularAutoConfiguration()
+		.and(ArchitectureRules.areNotKotlinClasses());
 
 	EvaluationResult check(JavaClasses javaClasses) {
 		AutoConfigurations autoConfigurations = new AutoConfigurations();

documentation/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/developingautoconfiguration/conditionannotations/classconditions/MyAutoConfiguration.java

@@ -30,11 +30,11 @@ public final class MyAutoConfiguration {
 
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(SomeService.class)
-	public static class SomeServiceConfiguration {
+	static class SomeServiceConfiguration {
 
 		@Bean
 		@ConditionalOnMissingBean
-		public SomeService someService() {
+		SomeService someService() {
 			return new SomeService();
 		}