Adopt naming conventions for constant fields

* public, protected and package-private constants must be upper case
* private constants may have any case
  * except for logger which must be lowercase.

Author: mpkorstanje

CONTRIBUTING.md

@@ -54,6 +54,8 @@ I hereby agree to the terms of the JUnit Contributor License Agreement.
 
 ### Naming Conventions
 
+Acronyms are words.
+
 Whenever an acronym is included as part of a type name or method name, keep the first
 letter of the acronym uppercase and use lowercase for the rest of the acronym. Otherwise,
 it becomes _impossible_ to perform camel-cased searches in IDEs, and it becomes
@@ -119,6 +121,17 @@ code -- class names, method names, variable names, etc.
 See [`ExtensionContext`](junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java) and
 [`ParameterContext`](junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterContext.java) for example Javadoc.
 
+### Constant fields
+
+A constant field is a `static final` field whose value is immutable. If a static final
+field has a primitive type or an immutable reference type it is a constant field.
+
+- To minimize accessibility and mutability for all non-private `static final` fields
+  under `src/main` should be constant fields.
+- Constant fields should be named using uppercase words separated by underscores. For
+  example `DEFAULT_HTTP_URL_PROVIDER`.
+
+Note: `org.junit.platform.commons.logging.Logger` is considered mutable.
 
 ### Nullability
 

documentation/src/tools/java/org/junit/api/tools/ApiReportGenerator.java

@@ -48,7 +48,7 @@
  */
 class ApiReportGenerator {
 
-	private static final Logger LOGGER = LoggerFactory.getLogger(ApiReportGenerator.class);
+	private static final Logger logger = LoggerFactory.getLogger(ApiReportGenerator.class);
 	private static final String EOL = System.lineSeparator();
 
 	public static void main(String... args) {
@@ -160,7 +160,7 @@ private static SortedSet<ClassInfo> collectTypes(ScanResult scanResult) {
 				.filter(it -> !it.getAnnotationInfo(API.class).isInherited()) //
 				.collect(toCollection(TreeSet::new));
 
-		LOGGER.debug(() -> {
+		logger.debug(() -> {
 			var builder = new StringBuilder("Listing of all " + types.size() + " annotated types:");
 			builder.append(EOL);
 			types.forEach(e -> builder.append(e.getName()).append(EOL));

gradle/config/checkstyle/checkstyleMain.xml

@@ -48,6 +48,20 @@
 		<module name="EqualsAvoidNull"/>
 		<module name="EmptyStatement"/>
 		<module name="MissingDeprecated"/>
+		<!-- non-private static final fields must be constants and named accordingly.
+		 	 See CONTRIBUTING.md - Constant fields -->
+		<module name="ConstantName">
+			<property name="applyToPrivate" value="false"/>
+		</module>
+		<module name="ConstantName">
+			<!-- private static final fields may be mutable or immutable.
+				 But logger is always mutable. See CONTRIBUTING.md - Constant fields -->
+			<property name="format" value="^(?!^LOGGER$).*$"/>
+			<property name="applyToPublic" value="false"/>
+			<property name="applyToProtected" value="false"/>
+			<property name="applyToPackage" value="false"/>
+		</module>
+
 	</module>
 
 	<module name="JavadocPackage" />

junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDirDeletionStrategy.java

@@ -96,7 +96,7 @@ DeletionResult delete(Path tempDir, AnnotatedElementContext elementContext, Exte
 	 */
 	final class IgnoreFailures implements TempDirDeletionStrategy {
 
-		private static final Logger LOGGER = LoggerFactory.getLogger(IgnoreFailures.class);
+		private static final Logger logger = LoggerFactory.getLogger(IgnoreFailures.class);
 		private final TempDirDeletionStrategy delegate;
 
 		/**
@@ -123,7 +123,7 @@ public DeletionResult delete(Path tempDir, AnnotatedElementContext elementContex
 		}
 
 		private void logWarning(AnnotatedElementContext elementContext, DeletionException exception) {
-			LOGGER.warn(exception, () -> "Failed to delete all temporary files for %s".formatted(
+			logger.warn(exception, () -> "Failed to delete all temporary files for %s".formatted(
 				descriptionFor(elementContext.getAnnotatedElement())));
 		}
 
@@ -169,7 +169,7 @@ final class Standard implements TempDirDeletionStrategy {
 		 */
 		public static final Standard INSTANCE = new Standard();
 
-		private static final Logger LOGGER = LoggerFactory.getLogger(Standard.class);
+		private static final Logger logger = LoggerFactory.getLogger(Standard.class);
 
 		private Standard() {
 		}
@@ -201,7 +201,7 @@ private void delete(Path tempDir, FileOperations fileOperations, BiConsumer<Path
 
 				@Override
 				public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
-					LOGGER.trace(() -> "preVisitDirectory: " + dir);
+					logger.trace(() -> "preVisitDirectory: " + dir);
 					if (isLinkWithTargetOutsideTempDir(dir)) {
 						warnAboutLinkWithTargetOutsideTempDir("link", dir);
 						delete(dir, fileOperations);
@@ -215,7 +215,7 @@ public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) th
 
 				@Override
 				public FileVisitResult visitFileFailed(Path file, IOException exc) {
-					LOGGER.trace(exc, () -> "visitFileFailed: " + file);
+					logger.trace(exc, () -> "visitFileFailed: " + file);
 					if (exc instanceof NoSuchFileException && !Files.exists(file, LinkOption.NOFOLLOW_LINKS)) {
 						return CONTINUE;
 					}
@@ -226,7 +226,7 @@ public FileVisitResult visitFileFailed(Path file, IOException exc) {
 
 				@Override
 				public FileVisitResult visitFile(Path file, BasicFileAttributes attributes) throws IOException {
-					LOGGER.trace(() -> "visitFile: " + file);
+					logger.trace(() -> "visitFile: " + file);
 					if (Files.isSymbolicLink(file) && isLinkWithTargetOutsideTempDir(file)) {
 						warnAboutLinkWithTargetOutsideTempDir("symbolic link", file);
 					}
@@ -236,7 +236,7 @@ public FileVisitResult visitFile(Path file, BasicFileAttributes attributes) thro
 
 				@Override
 				public FileVisitResult postVisitDirectory(Path dir, @Nullable IOException exc) {
-					LOGGER.trace(exc, () -> "postVisitDirectory: " + dir);
+					logger.trace(exc, () -> "postVisitDirectory: " + dir);
 					delete(dir, fileOperations);
 					return CONTINUE;
 				}
@@ -248,15 +248,15 @@ private boolean isLinkWithTargetOutsideTempDir(Path path) {
 						return !path.toRealPath().startsWith(rootRealPath);
 					}
 					catch (IOException e) {
-						LOGGER.trace(e,
+						logger.trace(e,
 							() -> "Failed to determine real path for " + path + "; assuming it is not a link");
 						return false;
 					}
 				}
 
 				private void warnAboutLinkWithTargetOutsideTempDir(String linkType, Path file) throws IOException {
 					Path realPath = file.toRealPath();
-					LOGGER.warn(() -> """
+					logger.warn(() -> """
 							Deleting %s from location inside of temp dir (%s) \
 							to location outside of temp dir (%s) but not the target file/directory""".formatted(
 						linkType, file, realPath));
@@ -303,13 +303,13 @@ private void resetPermissionsAndTryToDeleteAgain(Path path, IOException exceptio
 		}
 
 		private void deleteWithLogging(Path file, FileOperations fileOperations) throws IOException {
-			LOGGER.trace(() -> "Attempting to delete " + file);
+			logger.trace(() -> "Attempting to delete " + file);
 			try {
 				fileOperations.delete(file);
-				LOGGER.trace(() -> "Successfully deleted " + file);
+				logger.trace(() -> "Successfully deleted " + file);
 			}
 			catch (IOException e) {
-				LOGGER.trace(e, () -> "Failed to delete " + file);
+				logger.trace(e, () -> "Failed to delete " + file);
 				throw e;
 			}
 		}

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/AbstractExtensionContext.java

@@ -54,7 +54,7 @@
  */
 abstract class AbstractExtensionContext<T extends TestDescriptor> implements ExtensionContextInternal, AutoCloseable {
 
-	private static final Logger LOGGER = LoggerFactory.getLogger(AbstractExtensionContext.class);
+	private static final Logger logger = LoggerFactory.getLogger(AbstractExtensionContext.class);
 	private static final Namespace CLOSEABLE_RESOURCE_LOGGING_NAMESPACE = Namespace.create(
 		AbstractExtensionContext.class, "CloseableResourceLogging");
 
@@ -113,7 +113,7 @@ private <N> NamespacedHierarchicalStore.CloseAction<N> createCloseAction() {
 			if (value instanceof Store.CloseableResource resource) {
 				if (isAutoCloseEnabled) {
 					store.computeIfAbsent(value.getClass(), type -> {
-						LOGGER.warn(() -> "Type implements CloseableResource but not AutoCloseable: " + type.getName());
+						logger.warn(() -> "Type implements CloseableResource but not AutoCloseable: " + type.getName());
 						return true;
 					});
 				}

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java

@@ -334,17 +334,17 @@ public void close() {
 
 	record Cleanup(CleanupMode cleanupMode, Supplier<TempDirDeletionStrategy> deletionStrategy) {
 
-		private static final Logger LOGGER = LoggerFactory.getLogger(Cleanup.class);
+		private static final Logger logger = LoggerFactory.getLogger(Cleanup.class);
 
 		void run(Path dir, AnnotatedElementContext elementContext, ExtensionContext extensionContext)
 				throws IOException {
 			if (cleanupMode == NEVER || (cleanupMode == ON_SUCCESS && selfOrChildFailed(extensionContext))) {
-				LOGGER.info(() -> "Skipping cleanup of temp dir %s for %s due to CleanupMode.%s.".formatted(dir,
+				logger.info(() -> "Skipping cleanup of temp dir %s for %s due to CleanupMode.%s.".formatted(dir,
 					descriptionFor(elementContext.getAnnotatedElement()), cleanupMode.name()));
 				return;
 			}
 
-			LOGGER.trace(() -> "Cleaning up temp dir " + dir);
+			logger.trace(() -> "Cleaning up temp dir " + dir);
 			if (Files.exists(dir)) {
 				deletionStrategy.get().delete(dir, elementContext, extensionContext) //
 						.toException() //