Refine inner class detection algorithm

Update the ConfigurationMetadataAnnotationProcessor nested class
algorithm to prevent inner classes being added as both groups and
properties.

Fixes gh-1975

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

@@ -175,8 +175,9 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 			ExecutableElement getter = entry.getValue();
 			ExecutableElement setter = members.getPublicSetters().get(name);
 			VariableElement field = members.getFields().get(name);
-			boolean isNested = getAnnotation(field,
+			Element returnType = this.processingEnv.getTypeUtils().asElement(
-					nestedConfigurationPropertyAnnotation()) != null;
+					getter.getReturnType());
+			boolean isNested = isNested(returnType, field, element);
 			boolean isCollection = this.typeUtils.isCollectionOrMap(getter
 					.getReturnType());
 			if (!isNested && (setter != null || isCollection)) {
@@ -203,22 +204,25 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 					getter.getReturnType());
 			AnnotationMirror annotation = getAnnotation(getter,
 					configurationPropertiesAnnotation());
-			boolean isNested = getAnnotation(field,
+			boolean isNested = isNested(returnType, field, element);
-					nestedConfigurationPropertyAnnotation()) != null;
 			if (returnType != null && returnType instanceof TypeElement
-					&& annotation == null) {
+					&& annotation == null && isNested) {
-				TypeElement returns = (TypeElement) returnType;
+				String nestedPrefix = ConfigurationMetadata.nestedPrefix(prefix, name);
-				if ((this.typeUtils.isEnclosedIn(returnType, element) && returnType
-						.getKind() != ElementKind.ENUM) || isNested) {
-					String nestedPrefix = ConfigurationMetadata
-							.nestedPrefix(prefix, name);
 				this.metadata.add(ItemMetadata.newGroup(nestedPrefix,
-							this.typeUtils.getType(returns),
+						this.typeUtils.getType(returnType),
 						this.typeUtils.getType(element), getter.toString()));
-					processTypeElement(nestedPrefix, returns);
+				processTypeElement(nestedPrefix, (TypeElement) returnType);
 			}
 		}
 	}
+
+	private boolean isNested(Element returnType, VariableElement field,
+			TypeElement element) {
+		if (getAnnotation(field, nestedConfigurationPropertyAnnotation()) != null) {
+			return true;
+		}
+		return this.typeUtils.isEnclosedIn(returnType, element)
+				&& returnType.getKind() != ElementKind.ENUM;
 	}
 
 	private boolean hasDeprecateAnnotation(Element element) {

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

@@ -236,17 +236,14 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 		assertThat(metadata, containsProperty("config.first.name"));
 		assertThat(metadata, containsProperty("config.first.bar.name"));
 		assertThat(metadata,
-				containsProperty("config.the-second", InnerClassProperties.Foo.class)
+				containsGroup("config.the-second", InnerClassProperties.Foo.class)
 						.fromSource(InnerClassProperties.class));
 		assertThat(metadata, containsProperty("config.the-second.name"));
 		assertThat(metadata, containsProperty("config.the-second.bar.name"));
 		assertThat(metadata, containsGroup("config.third").ofType(SimplePojo.class)
 				.fromSource(InnerClassProperties.class));
 		assertThat(metadata, containsProperty("config.third.value"));
-		assertThat(
+		assertThat(metadata, containsProperty("config.fourth"));
-				metadata,
-				containsProperty("config.fourth").ofType(
-						InnerClassProperties.Fourth.class));
 		assertThat(metadata, not(containsGroup("config.fourth")));
 	}
 

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

@@ -119,10 +119,13 @@ public class ConfigurationMetadataMatchers {
 			ConfigurationMetadata metadata = (ConfigurationMetadata) item;
 			ItemMetadata property = getFirstPropertyWithName(metadata, this.name);
 			if (property == null) {
-				description.appendText("missing property " + this.name);
+				description.appendText("missing "
+						+ this.itemType.toString().toLowerCase() + " " + this.name);
 			}
 			else {
-				description.appendText("was property ").appendValue(property);
+				description.appendText(
+						"was " + this.itemType.toString().toLowerCase() + " ")
+						.appendValue(property);
 			}
 		}