Relax @ConstructorBinding member class requirement

Update `@ConfigurationProperties` so that `@ConstructorBinding` classes
no longer need to repeat the annotation for their members.

Closes gh-18481

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/PropertyDescriptorResolver.java

@@ -23,6 +23,7 @@ import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import javax.lang.model.element.ExecutableElement;
+import javax.lang.model.element.NestingKind;
 import javax.lang.model.element.TypeElement;
 import javax.lang.model.element.VariableElement;
 import javax.lang.model.type.TypeMirror;
@@ -169,13 +170,24 @@ class PropertyDescriptorResolver {
 		}
 
 		static ConfigurationPropertiesTypeElement of(TypeElement type, MetadataGenerationEnvironment env) {
-			boolean constructorBoundType = env.hasConstructorBindingAnnotation(type);
+			boolean constructorBoundType = isConstructorBoundType(type, env);
 			List<ExecutableElement> constructors = ElementFilter.constructorsIn(type.getEnclosedElements());
 			List<ExecutableElement> boundConstructors = constructors.stream()
 					.filter(env::hasConstructorBindingAnnotation).collect(Collectors.toList());
 			return new ConfigurationPropertiesTypeElement(type, constructorBoundType, constructors, boundConstructors);
 		}
 
+		private static boolean isConstructorBoundType(TypeElement type, MetadataGenerationEnvironment env) {
+			if (env.hasConstructorBindingAnnotation(type)) {
+				return true;
+			}
+			if (type.getNestingKind() == NestingKind.MEMBER) {
+				return isConstructorBoundType((TypeElement) type.getEnclosingElement(), env);
+			}
+			return false;
+
+		}
+
 	}
 
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/DeducedImmutablePropertiesMetadataGenerationTests.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2012-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationprocessor;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.Metadata;
+import org.springframework.boot.configurationsample.immutable.DeducedImmutableClassProperties;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Metadata generation tests for immutable properties deduced because they're nested.
+ *
+ * @author Phillip Webb
+ */
+class DeducedImmutablePropertiesMetadataGenerationTests extends AbstractMetadataGenerationTests {
+
+	@Test
+	void immutableSimpleProperties() {
+		ConfigurationMetadata metadata = compile(DeducedImmutableClassProperties.class);
+		assertThat(metadata).has(Metadata.withGroup("test").fromSource(DeducedImmutableClassProperties.class));
+		assertThat(metadata).has(Metadata.withProperty("test.nested.name", String.class));
+	}
+
+}

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/immutable/DeducedImmutableClassProperties.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2012-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationsample.immutable;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+import org.springframework.boot.configurationsample.ConstructorBinding;
+
+/**
+ * Inner properties, in immutable format.
+ *
+ * @author Phillip Webb
+ */
+@ConfigurationProperties("test")
+@ConstructorBinding
+public class DeducedImmutableClassProperties {
+
+	private final Nested nested;
+
+	public DeducedImmutableClassProperties(Nested nested) {
+		this.nested = nested;
+	}
+
+	public Nested getNested() {
+		return this.nested;
+	}
+
+	public static class Nested {
+
+		private String name;
+
+		public Nested(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+	}
+
+}