Detect nested types that are not directly nested to the current type

This commit makes sure that sub-namespace that are defined in a flat
manner in a configuration properties are considered for runtime hints

Closes gh-36909

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

@@ -318,13 +318,20 @@ private boolean isMap(ResolvableType type) {
 		 */
 		private boolean isNestedType(String propertyName, Class<?> propertyType) {
 			Class<?> declaringClass = propertyType.getDeclaringClass();
-			if (declaringClass != null && declaringClass.isAssignableFrom(this.type)) {
+			if (declaringClass != null && isNested(declaringClass, this.type)) {
 				return true;
 			}
 			Field field = ReflectionUtils.findField(this.type, propertyName);
 			return (field != null) && MergedAnnotations.from(field).isPresent(Nested.class);
 		}
 
+		private static boolean isNested(Class<?> type, Class<?> candidate) {
+			if (type.isAssignableFrom(candidate)) {
+				return true;
+			}
+			return (candidate.getDeclaringClass() != null && isNested(type, candidate.getDeclaringClass()));
+		}
+
 		private boolean isJavaType(Class<?> candidate) {
 			return candidate.getPackageName().startsWith("java.");
 		}

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

@@ -35,6 +35,9 @@
 import org.springframework.boot.context.properties.ConfigurationPropertiesBean;
 import org.springframework.boot.context.properties.NestedConfigurationProperty;
 import org.springframework.boot.context.properties.bind.BindableRuntimeHintsRegistrarTests.BaseProperties.InheritedNested;
+import org.springframework.boot.context.properties.bind.BindableRuntimeHintsRegistrarTests.ComplexNestedProperties.ListenerRetry;
+import org.springframework.boot.context.properties.bind.BindableRuntimeHintsRegistrarTests.ComplexNestedProperties.Retry;
+import org.springframework.boot.context.properties.bind.BindableRuntimeHintsRegistrarTests.ComplexNestedProperties.Simple;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
 import org.springframework.context.EnvironmentAware;
@@ -259,6 +262,23 @@ void registerHintsWhenHasInheritedNestedProperties() {
 			.satisfies(javaBeanBinding(InheritedNested.class, "getAlpha", "setAlpha"));
 	}
 
+	@Test
+	void registerHintsWhenHasComplexNestedProperties() {
+		RuntimeHints runtimeHints = registerHints(ComplexNestedProperties.class);
+		assertThat(runtimeHints.reflection().typeHints()).hasSize(4);
+		assertThat(runtimeHints.reflection().getTypeHint(Retry.class)).satisfies((entry) -> {
+			assertThat(entry.getMemberCategories()).isEmpty();
+			assertThat(entry.methods()).extracting(ExecutableHint::getName)
+				.containsExactlyInAnyOrder("getCount", "setCount");
+		});
+		assertThat(runtimeHints.reflection().getTypeHint(ListenerRetry.class))
+			.satisfies(javaBeanBinding(ListenerRetry.class, "isStateless", "setStateless"));
+		assertThat(runtimeHints.reflection().getTypeHint(Simple.class))
+			.satisfies(javaBeanBinding(Simple.class, "getRetry"));
+		assertThat(runtimeHints.reflection().getTypeHint(ComplexNestedProperties.class))
+			.satisfies(javaBeanBinding(ComplexNestedProperties.class, "getSimple"));
+	}
+
 	private Consumer<TypeHint> javaBeanBinding(Class<?> type, String... expectedMethods) {
 		return javaBeanBinding(type, type.getDeclaredConstructors()[0], expectedMethods);
 	}
@@ -723,4 +743,52 @@ public void setBravo(String bravo) {
 
 	}
 
+	public static class ComplexNestedProperties {
+
+		private final Simple simple = new Simple();
+
+		public Simple getSimple() {
+			return this.simple;
+		}
+
+		public static class Simple {
+
+			private final ListenerRetry retry = new ListenerRetry();
+
+			public ListenerRetry getRetry() {
+				return this.retry;
+			}
+
+		}
+
+		public abstract static class Retry {
+
+			private int count = 5;
+
+			public int getCount() {
+				return this.count;
+			}
+
+			public void setCount(int count) {
+				this.count = count;
+			}
+
+		}
+
+		public static class ListenerRetry extends Retry {
+
+			private boolean stateless;
+
+			public boolean isStateless() {
+				return this.stateless;
+			}
+
+			public void setStateless(boolean stateless) {
+				this.stateless = stateless;
+			}
+
+		}
+
+	}
+
 }