Ensure ReflectionUtils.findFields() returns distinct fields

Closes #3646

Author: sbrannen

documentation/src/docs/asciidoc/release-notes/release-notes-5.11.0-M1.adoc

@@ -16,7 +16,7 @@ repository on GitHub.
 [[release-notes-5.11.0-M1-junit-platform-bug-fixes]]
 ==== Bug Fixes
 
-* ❓
+* `ReflectionSupport.findFields(...)` now returns a distinct set of fields.
 
 [[release-notes-5.11.0-M1-junit-platform-deprecations-and-breaking-changes]]
 ==== Deprecations and Breaking Changes

junit-platform-commons/src/main/java/org/junit/platform/commons/support/AnnotationSupport.java

@@ -262,8 +262,8 @@ public static List<Field> findPublicAnnotatedFields(Class<?> clazz, Class<?> fie
 	}
 
 	/**
-	 * Find all {@linkplain Field fields} of the supplied class or interface
-	 * that are annotated or <em>meta-annotated</em> with the specified
+	 * Find all distinct {@linkplain Field fields} of the supplied class or
+	 * interface that are annotated or <em>meta-annotated</em> with the specified
 	 * {@code annotationType}, using top-down search semantics within the type
 	 * hierarchy.
 	 *
@@ -289,8 +289,8 @@ public static List<Field> findAnnotatedFields(Class<?> clazz, Class<? extends An
 	}
 
 	/**
-	 * Find all {@linkplain Field fields} of the supplied class or interface
-	 * that are annotated or <em>meta-annotated</em> with the specified
+	 * Find all distinct {@linkplain Field fields} of the supplied class or
+	 * interface that are annotated or <em>meta-annotated</em> with the specified
 	 * {@code annotationType} and match the specified {@code predicate}, using
 	 * top-down search semantics within the type hierarchy.
 	 *
@@ -318,8 +318,8 @@ public static List<Field> findAnnotatedFields(Class<?> clazz, Class<? extends An
 	}
 
 	/**
-	 * Find all {@linkplain Field fields} of the supplied class or interface
-	 * that are annotated or <em>meta-annotated</em> with the specified
+	 * Find all distinct {@linkplain Field fields} of the supplied class or
+	 * interface that are annotated or <em>meta-annotated</em> with the specified
 	 * {@code annotationType} and match the specified {@code predicate}, using
 	 * the supplied hierarchy traversal mode.
 	 *

junit-platform-commons/src/main/java/org/junit/platform/commons/support/ReflectionSupport.java

@@ -298,8 +298,8 @@ public static Object invokeMethod(Method method, Object target, Object... args)
 	}
 
 	/**
-	 * Find all {@linkplain Field fields} of the supplied class or interface
-	 * that match the specified {@code predicate}.
+	 * Find all distinct {@linkplain Field fields} of the supplied class or
+	 * interface that match the specified {@code predicate}.
 	 *
 	 * <p>Fields declared in the same class or interface will be ordered using
 	 * an algorithm that is deterministic but intentionally nonobvious.
@@ -325,8 +325,8 @@ public static List<Field> findFields(Class<?> clazz, Predicate<Field> predicate,
 	}
 
 	/**
-	 * Find all {@linkplain Field fields} of the supplied class or interface
-	 * that match the specified {@code predicate}.
+	 * Find all distinct {@linkplain Field fields} of the supplied class or
+	 * interface that match the specified {@code predicate}.
 	 *
 	 * <p>Fields declared in the same class or interface will be ordered using
 	 * an algorithm that is deterministic but intentionally nonobvious.

junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java

@@ -1202,7 +1202,11 @@ public static Stream<Field> streamFields(Class<?> clazz, Predicate<Field> predic
 		Preconditions.notNull(predicate, "Predicate must not be null");
 		Preconditions.notNull(traversalMode, "HierarchyTraversalMode must not be null");
 
-		return findAllFieldsInHierarchy(clazz, traversalMode).stream().filter(predicate);
+		// @formatter:off
+		return findAllFieldsInHierarchy(clazz, traversalMode).stream()
+				.filter(predicate)
+				.distinct();
+		// @formatter:on
 	}
 
 	private static List<Field> findAllFieldsInHierarchy(Class<?> clazz, HierarchyTraversalMode traversalMode) {

platform-tests/src/test/java/org/junit/platform/commons/util/ReflectionUtilsTests.java

@@ -1406,6 +1406,25 @@ void readFieldValuesFromClass() {
 		assertThat(values).containsExactly(2.5, "constant", 99);
 	}
 
+	/**
+	 * @see https://github.com/junit-team/junit5/issues/3646
+	 * @since 1.11
+	 */
+	@Test
+	void readFieldValuesFromInteracesAndClassesInTypeHierarchy() {
+		var fields = findFields(InterfaceWithField.class, ReflectionUtils::isStatic, TOP_DOWN);
+		var values = ReflectionUtils.readFieldValues(fields, null);
+		assertThat(values).containsOnly("ifc");
+
+		fields = findFields(SuperclassWithFieldAndFieldFromInterface.class, ReflectionUtils::isStatic, TOP_DOWN);
+		values = ReflectionUtils.readFieldValues(fields, null);
+		assertThat(values).containsExactly("ifc", "super");
+
+		fields = findFields(SubclassWithFieldAndFieldFromInterface.class, ReflectionUtils::isStatic, TOP_DOWN);
+		values = ReflectionUtils.readFieldValues(fields, null);
+		assertThat(values).containsExactly("ifc", "super", "sub");
+	}
+
 	@Test
 	void readFieldValuesFromInstanceWithTypeFilterForString() {
 		var fields = findFields(ClassWithFields.class, isA(String.class), TOP_DOWN);
@@ -1942,6 +1961,22 @@ public static class ClassWithFields {
 
 	}
 
+	interface InterfaceWithField {
+
+		String interfacePath = "ifc";
+	}
+
+	static class SuperclassWithFieldAndFieldFromInterface implements InterfaceWithField {
+
+		static final String superPath = "super";
+	}
+
+	static class SubclassWithFieldAndFieldFromInterface extends SuperclassWithFieldAndFieldFromInterface
+			implements InterfaceWithField {
+
+		static final String subPath = "sub";
+	}
+
 	@SuppressWarnings("unused")
 	private static class ClassWithOneCustomConstructor {