Align cascading of config prop validation with bean validation spec

Closes gh-40345

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/features/external-config.adoc

@@ -1178,7 +1178,7 @@ include-code::MyProperties[]
 
 TIP: You can also trigger validation by annotating the `@Bean` method that creates the configuration properties with `@Validated`.
 
-To ensure that validation is always triggered for nested properties, even when no properties are found, the associated field must be annotated with `@Valid`.
+To cascade validation to nested properties the associated field must be annotated with `@Valid`.
 The following example builds on the preceding `MyProperties` example:
 
 include-code::nested/MyProperties[]

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBinder.java

@@ -76,8 +76,6 @@ class ConfigurationPropertiesBinder {
 
 	private final boolean jsr303Present;
 
-	private volatile Validator jsr303Validator;
-
 	private volatile Binder binder;
 
 	ConfigurationPropertiesBinder(ApplicationContext applicationContext) {
@@ -141,7 +139,7 @@ private List<Validator> getValidators(Bindable<?> target) {
 			validators.add(this.configurationPropertiesValidator);
 		}
 		if (this.jsr303Present && target.getAnnotation(Validated.class) != null) {
-			validators.add(getJsr303Validator());
+			validators.add(getJsr303Validator(target.getType().resolve()));
 		}
 		Validator selfValidator = getSelfValidator(target);
 		if (selfValidator != null) {
@@ -162,11 +160,8 @@ private Validator getSelfValidator(Bindable<?> target) {
 		return null;
 	}
 
-	private Validator getJsr303Validator() {
-		if (this.jsr303Validator == null) {
-			this.jsr303Validator = new ConfigurationPropertiesJsr303Validator(this.applicationContext);
-		}
-		return this.jsr303Validator;
+	private Validator getJsr303Validator(Class<?> type) {
+		return new ConfigurationPropertiesJsr303Validator(this.applicationContext, type);
 	}
 
 	private List<ConfigurationPropertiesBindHandlerAdvisor> getBindHandlerAdvisors() {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesJsr303Validator.java

@@ -37,13 +37,16 @@ final class ConfigurationPropertiesJsr303Validator implements Validator {
 
 	private final Delegate delegate;
 
-	ConfigurationPropertiesJsr303Validator(ApplicationContext applicationContext) {
+	private final Class<?> validatedType;
+
+	ConfigurationPropertiesJsr303Validator(ApplicationContext applicationContext, Class<?> validatedType) {
 		this.delegate = new Delegate(applicationContext);
+		this.validatedType = validatedType;
 	}
 
 	@Override
 	public boolean supports(Class<?> type) {
-		return this.delegate.supports(type);
+		return this.validatedType.equals(type) && this.delegate.supports(type);
 	}
 
 	@Override

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/ConfigurationPropertiesTests.java

@@ -106,6 +106,7 @@
 import static org.assertj.core.api.Assertions.assertThatException;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.assertj.core.api.Assertions.assertThatNoException;
 import static org.assertj.core.api.Assertions.entry;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
@@ -525,10 +526,9 @@ void loadValidatedOnBeanMethodAndJsr303ConstraintDoesNotMatchShouldFail() {
 	}
 
 	@Test
-	void loadWhenJsr303ConstraintDoesNotMatchOnNestedThatIsNotDirectlyAnnotatedShouldFail() {
-		assertThatExceptionOfType(ConfigurationPropertiesBindException.class)
-			.isThrownBy(() -> load(ValidatedNestedJsr303Properties.class, "properties.description="))
-			.withCauseInstanceOf(BindException.class);
+	void loadWhenJsr303ConstraintDoesNotMatchOnNestedThatIsNotAnnotatedWithValidShouldNotFail() {
+		assertThatNoException()
+			.isThrownBy(() -> load(ValidatedNestedJsr303Properties.class, "properties.description="));
 	}
 
 	@Test
@@ -1837,7 +1837,7 @@ static class NonValidatedJsr303Properties extends Jsr303Properties {
 	@Validated
 	static class ValidatedNestedJsr303Properties {
 
-		private Jsr303Properties properties;
+		private final Jsr303Properties properties = new Jsr303Properties();
 
 		Jsr303Properties getProperties() {
 			return this.properties;
@@ -1851,9 +1851,9 @@ Jsr303Properties getProperties() {
 	static class ValidatedValidNestedJsr303Properties {
 
 		@Valid
-		private final List<Jsr303Properties> properties = Collections.singletonList(new Jsr303Properties());
+		private final Jsr303Properties properties = new Jsr303Properties();
 
-		List<Jsr303Properties> getProperties() {
+		Jsr303Properties getProperties() {
 			return this.properties;
 		}