Generate hints for nested generics in configuration properties

See gh-31708

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

@@ -163,7 +163,7 @@ public final class ConfigurationPropertiesReflectionHintsProcessor {
 		if (propertyClass == null) {
 			return true;
 		}
-		if (getComponentType(propertyType) != null) {
+		if (isContainer(propertyType)) {
 			return false;
 		}
 		return !isNestedType(propertyName, propertyClass);
@@ -171,21 +171,43 @@ public final class ConfigurationPropertiesReflectionHintsProcessor {
 
 	private Class<?> getComponentType(ResolvableType propertyType) {
 		Class<?> propertyClass = propertyType.toClass();
+		ResolvableType componentType = null;
 		if (propertyType.isArray()) {
-			return propertyType.getComponentType().toClass();
+			componentType = propertyType.getComponentType();
 		}
 		else if (Collection.class.isAssignableFrom(propertyClass)) {
-			return propertyType.as(Collection.class).getGeneric(0).toClass();
+			componentType = propertyType.asCollection().getGeneric(0);
 		}
 		else if (Map.class.isAssignableFrom(propertyClass)) {
-			return propertyType.as(Map.class).getGeneric(1).toClass();
+			componentType = propertyType.asMap().getGeneric(1);
 		}
-		return null;
+		if (componentType == null) {
+			return null;
+		}
+		if (isContainer(componentType)) {
+			// Resolve nested generics like Map<String, List<SomeType>>
+			return getComponentType(componentType);
+		}
+		return componentType.toClass();
+	}
+
+	private boolean isContainer(ResolvableType type) {
+		if (type.isArray()) {
+			return true;
+		}
+		if (Collection.class.isAssignableFrom(type.toClass())) {
+			return true;
+		}
+		else if (Map.class.isAssignableFrom(type.toClass())) {
+			return true;
+		}
+		return false;
 	}
 
 	/**
 	 * Specify whether the specified property refer to a nested type. A nested type
-	 * represents a sub-namespace that need to be fully resolved.
+	 * represents a sub-namespace that need to be fully resolved. Nested types are either
+	 * inner classes or annotated with {@link NestedConfigurationProperty}.
 	 * @param propertyName the name of the property
 	 * @param propertyType the type of the property
 	 * @return whether the specified {@code propertyType} is a nested type

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

@@ -19,6 +19,7 @@ package org.springframework.boot.context.properties;
 import java.lang.reflect.Constructor;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Consumer;
@@ -34,6 +35,7 @@ import org.springframework.aot.hint.MemberCategory;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.TypeHint;
 import org.springframework.aot.hint.TypeReference;
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
 import org.springframework.beans.factory.aot.AotFactoriesLoader;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotContribution;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor;
@@ -53,6 +55,7 @@ import static org.mockito.Mockito.mock;
  * Tests for {@link ConfigurationPropertiesBeanFactoryInitializationAotProcessor}.
  *
  * @author Stephane Nicoll
+ * @author Moritz Halbritter
  */
 class ConfigurationPropertiesBeanFactoryInitializationAotProcessorTests {
 
@@ -227,6 +230,31 @@ class ConfigurationPropertiesBeanFactoryInitializationAotProcessorTests {
 				.anySatisfy(javaBeanBinding(GenericObject.class));
 	}
 
+	@Test
+	void processConfigurationPropertiesWithNestedGenerics() {
+		RuntimeHints runtimeHints = process(NestedGenerics.class);
+		assertThat(RuntimeHintsPredicates.reflection().onType(NestedGenerics.class)
+				.withMemberCategories(MemberCategory.INVOKE_DECLARED_METHODS, MemberCategory.INVOKE_PUBLIC_METHODS))
+						.accepts(runtimeHints);
+		assertThat(RuntimeHintsPredicates.reflection().onType(NestedGenerics.Nested.class)
+				.withMemberCategories(MemberCategory.INVOKE_DECLARED_METHODS, MemberCategory.INVOKE_PUBLIC_METHODS))
+						.accepts(runtimeHints);
+	}
+
+	@Test
+	void processConfigurationPropertiesWithMultipleNestedClasses() {
+		RuntimeHints runtimeHints = process(TripleNested.class);
+		assertThat(RuntimeHintsPredicates.reflection().onType(TripleNested.class)
+				.withMemberCategories(MemberCategory.INVOKE_DECLARED_METHODS, MemberCategory.INVOKE_PUBLIC_METHODS))
+						.accepts(runtimeHints);
+		assertThat(RuntimeHintsPredicates.reflection().onType(TripleNested.DoubleNested.class)
+				.withMemberCategories(MemberCategory.INVOKE_DECLARED_METHODS, MemberCategory.INVOKE_PUBLIC_METHODS))
+						.accepts(runtimeHints);
+		assertThat(RuntimeHintsPredicates.reflection().onType(TripleNested.DoubleNested.Nested.class)
+				.withMemberCategories(MemberCategory.INVOKE_DECLARED_METHODS, MemberCategory.INVOKE_PUBLIC_METHODS))
+						.accepts(runtimeHints);
+	}
+
 	private Consumer<TypeHint> javaBeanBinding(Class<?> type) {
 		return javaBeanBinding(type, type.getDeclaredConstructors()[0]);
 	}
@@ -590,4 +618,64 @@ class ConfigurationPropertiesBeanFactoryInitializationAotProcessorTests {
 
 	}
 
+	@ConfigurationProperties(prefix = "nested-generics")
+	public static class NestedGenerics {
+
+		private final Map<String, List<Nested>> nested = new HashMap<>();
+
+		public Map<String, List<Nested>> getNested() {
+			return this.nested;
+		}
+
+		public static class Nested {
+
+			private String field;
+
+			public String getField() {
+				return this.field;
+			}
+
+			public void setField(String field) {
+				this.field = field;
+			}
+
+		}
+
+	}
+
+	@ConfigurationProperties(prefix = "triple-nested")
+	public static class TripleNested {
+
+		private final DoubleNested doubleNested = new DoubleNested();
+
+		public DoubleNested getDoubleNested() {
+			return this.doubleNested;
+		}
+
+		public static class DoubleNested {
+
+			private final Nested nested = new Nested();
+
+			public Nested getNested() {
+				return this.nested;
+			}
+
+			public static class Nested {
+
+				private String field;
+
+				public String getField() {
+					return this.field;
+				}
+
+				public void setField(String field) {
+					this.field = field;
+				}
+
+			}
+
+		}
+
+	}
+
 }