Support the use of @AliasFor with @PropertyMapping

Previously, when @AliasFor was used, the value of the mapped property
would be incorrect as the value of the canonical attribute would be
used, rather than the value of the alias.

This commit updates AnnotationsPropertySource to use a merged annotation
as the source of attribute values, thereby ensuring that any aliased
attributes are configured correctly.

Closes gh-5821

spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/properties/AnnotationsPropertySource.java

@@ -18,12 +18,15 @@ package org.springframework.boot.test.autoconfigure.properties;
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.core.env.EnumerablePropertySource;
 import org.springframework.util.ObjectUtils;
@@ -55,26 +58,37 @@ public class AnnotationsPropertySource extends EnumerablePropertySource<Class<?>
 
 	private Map<String, Object> getProperties(Class<?> source) {
 		Map<String, Object> properties = new LinkedHashMap<String, Object>();
-		collectProperties(source, properties);
+		collectProperties(source, source, properties);
 		return Collections.unmodifiableMap(properties);
 	}
 
-	private void collectProperties(Class<?> source, Map<String, Object> properties) {
+	private void collectProperties(Class<?> root, Class<?> source,
+			Map<String, Object> properties) {
 		if (source != null) {
-			for (Annotation annotation : AnnotationUtils.getAnnotations(source)) {
+			for (Annotation annotation : getMergedAnnotations(root, source)) {
 				if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
-					annotation.annotationType().getAnnotation(PropertyMapping.class);
 					PropertyMapping typeMapping = annotation.annotationType()
 							.getAnnotation(PropertyMapping.class);
 					for (Method attribute : annotation.annotationType()
 							.getDeclaredMethods()) {
 						collectProperties(annotation, attribute, typeMapping, properties);
 					}
-					collectProperties(annotation.annotationType(), properties);
+					collectProperties(root, annotation.annotationType(), properties);
+				}
+			}
+			collectProperties(root, source.getSuperclass(), properties);
 		}
 	}
-			collectProperties(source.getSuperclass(), properties);
+
+	private List<Annotation> getMergedAnnotations(Class<?> root, Class<?> source) {
+		List<Annotation> mergedAnnotations = new ArrayList<Annotation>();
+		for (Annotation annotation : AnnotationUtils.getAnnotations(source)) {
+			if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
+				mergedAnnotations.add(AnnotatedElementUtils.getMergedAnnotation(root,
+						annotation.annotationType()));
+			}
 		}
+		return mergedAnnotations;
 	}
 
 	private void collectProperties(Annotation annotation, Method attribute,

spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/properties/AnnotationsPropertySourceTests.java

@@ -23,6 +23,8 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
+import org.springframework.core.annotation.AliasFor;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -154,6 +156,14 @@ public class AnnotationsPropertySourceTests {
 		assertThat(source.getProperty("test.example")).isEqualTo("charlie");
 	}
 
+	@Test
+	public void propertyMappedAttributesCanBeAliased() {
+		AnnotationsPropertySource source = new AnnotationsPropertySource(
+				PropertyMappedAttributeWithAnAlias.class);
+		assertThat(source.getPropertyNames()).containsExactly("aliasing.value");
+		assertThat(source.getProperty("aliasing.value")).isEqualTo("baz");
+	}
+
 	static class NoAnnotation {
 
 	}
@@ -307,4 +317,28 @@ public class AnnotationsPropertySourceTests {
 
 	}
 
+	@AttributeWithAliasAnnotation("baz")
+	static class PropertyMappedAttributeWithAnAlias {
+
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	@AliasedAttributeAnnotation
+	static @interface AttributeWithAliasAnnotation {
+
+		@AliasFor(annotation = AliasedAttributeAnnotation.class, attribute = "value")
+		String value() default "foo";
+
+		String someOtherAttribute() default "shouldNotBeMapped";
+
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	@PropertyMapping("aliasing")
+	static @interface AliasedAttributeAnnotation {
+
+		String value() default "bar";
+
+	}
+
 }