Make method signatures for Function parameters more flexible

Author: marcphilipp

documentation/src/docs/asciidoc/release-notes/release-notes-6.0.0-M1.adoc

@@ -76,6 +76,11 @@ repository on GitHub.
   property has been removed. JUnit now always adheres to standard Java semantics regarding
   whether a given field or method is visible or overridden according to the rules of the
   Java language.
+* The type bounds of the following methods have been changed to be more flexible and allow
+  nullable and non-nullable types:
+  - `ConfigurationParameters.get(String, Function)`
+  - `NamespacedHierarchicalStore.getOrComputeIfAbsent(N, K, Function)`
+  - `NamespacedHierarchicalStore.getOrComputeIfAbsent(N, K, Function, Class)`
 
 [[release-notes-6.0.0-M1-junit-platform-new-features-and-improvements]]
 ==== New Features and Improvements
@@ -112,6 +117,11 @@ repository on GitHub.
   `callsInPlace(executable, AT_MOST_ONCE)` which might result in compilation errors.
 * The `junit-jupiter-migrationsupport` artifact and its contained classes are now
   deprecated and will be removed in the next major version.
+* The type bounds of the following methods have been changed to be more flexible and allow
+  nullable and non-nullable types:
+  - `ExtensionContext.getConfigurationParameter(String, Function)`
+  - `ExtensionContext.getOrComputeIfAbsent(K, Function)`
+  - `ExtensionContext.getOrComputeIfAbsent(K, Function, Class)`
 
 [[release-notes-6.0.0-M1-junit-jupiter-new-features-and-improvements]]
 ==== New Features and Improvements

junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java

@@ -345,7 +345,7 @@ default Method getRequiredTestMethod() {
 	 * @see org.junit.platform.engine.ConfigurationParameters
 	 */
 	@API(status = STABLE, since = "5.10")
-	<T> Optional<T> getConfigurationParameter(String key, Function<String, T> transformer);
+	<T> Optional<T> getConfigurationParameter(String key, Function<? super String, ? extends @Nullable T> transformer);
 
 	/**
 	 * Publish a map of key-value pairs to be consumed by an
@@ -649,7 +649,8 @@ default <V> V getOrDefault(Object key, Class<V> requiredType, V defaultValue) {
 		 * @see CloseableResource
 		 * @see AutoCloseable
 		 */
-		<K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(K key, Function<? super K, ? extends V> defaultCreator);
+		<K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(K key,
+				Function<? super K, ? extends V> defaultCreator);
 
 		/**
 		 * Get the value of the specified required type that is stored under the
@@ -680,8 +681,8 @@ default <V> V getOrDefault(Object key, Class<V> requiredType, V defaultValue) {
 		 * @see CloseableResource
 		 * @see AutoCloseable
 		 */
-		<K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(K key, Function<? super K, ? extends V> defaultCreator,
-				Class<V> requiredType);
+		<K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(K key,
+				Function<? super K, ? extends V> defaultCreator, Class<V> requiredType);
 
 		/**
 		 * Store a {@code value} for later retrieval under the supplied {@code key}.

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/CachingJupiterConfiguration.java

@@ -59,7 +59,7 @@ public Optional<String> getRawConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> getRawConfigurationParameter(String key, Function<String, T> transformer) {
+	public <T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer) {
 		return delegate.getRawConfigurationParameter(key, transformer);
 	}
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java

@@ -120,7 +120,7 @@ public Optional<String> getRawConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> getRawConfigurationParameter(String key, Function<String, T> transformer) {
+	public <T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer) {
 		return configurationParameters.get(key, transformer);
 	}
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/JupiterConfiguration.java

@@ -57,7 +57,7 @@ public interface JupiterConfiguration {
 
 	Optional<String> getRawConfigurationParameter(String key);
 
-	<T> Optional<T> getRawConfigurationParameter(String key, Function<String, T> transformer);
+	<T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer);
 
 	boolean isParallelExecutionEnabled();
 

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

@@ -242,7 +242,8 @@ public Optional<String> getConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <V> Optional<V> getConfigurationParameter(String key, Function<String, V> transformer) {
+	public <V> Optional<V> getConfigurationParameter(String key,
+			Function<? super String, ? extends @Nullable V> transformer) {
 		return this.configuration.getRawConfigurationParameter(key, transformer);
 	}
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/NamespaceAwareStore.java

@@ -54,7 +54,8 @@ public NamespaceAwareStore(NamespacedHierarchicalStore<Namespace> valuesStore, N
 	}
 
 	@Override
-	public <K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(K key, Function<? super K, ? extends V> defaultCreator) {
+	public <K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(K key,
+			Function<? super K, ? extends V> defaultCreator) {
 		Preconditions.notNull(key, "key must not be null");
 		Preconditions.notNull(defaultCreator, "defaultCreator function must not be null");
 		Supplier<@Nullable Object> action = () -> this.valuesStore.getOrComputeIfAbsent(this.namespace, key,
@@ -63,8 +64,8 @@ public NamespaceAwareStore(NamespacedHierarchicalStore<Namespace> valuesStore, N
 	}
 
 	@Override
-	public <K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(K key, Function<? super K, ? extends V> defaultCreator,
-			Class<V> requiredType) {
+	public <K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(K key,
+			Function<? super K, ? extends V> defaultCreator, Class<V> requiredType) {
 		Preconditions.notNull(key, "key must not be null");
 		Preconditions.notNull(defaultCreator, "defaultCreator function must not be null");
 		Preconditions.notNull(requiredType, "requiredType must not be null");

junit-platform-engine/src/main/java/org/junit/platform/engine/ConfigurationParameters.java

@@ -117,7 +117,7 @@ public interface ConfigurationParameters {
 	 * @see #CONFIG_FILE_NAME
 	 */
 	@API(status = STABLE, since = "1.3")
-	default <T> Optional<T> get(String key, Function<String, ? extends @Nullable T> transformer) {
+	default <T> Optional<T> get(String key, Function<? super String, ? extends @Nullable T> transformer) {
 		Preconditions.notNull(transformer, "transformer must not be null");
 		return get(key).map(input -> {
 			try {

junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/PrefixedConfigurationParameters.java

@@ -58,7 +58,7 @@ public Optional<Boolean> getBoolean(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> get(String key, Function<String, ? extends @Nullable T> transformer) {
+	public <T> Optional<T> get(String key, Function<? super String, ? extends @Nullable T> transformer) {
 		return delegate.get(prefixed(key), transformer);
 	}
 

junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java

@@ -220,7 +220,8 @@ public void close() {
 	 * be cast to the required type, or if this store has already been closed
 	 */
 	public <K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(N namespace, K key,
-			Function<? super K, ? extends V> defaultCreator, Class<V> requiredType) throws NamespacedHierarchicalStoreException {
+			Function<? super K, ? extends V> defaultCreator, Class<V> requiredType)
+			throws NamespacedHierarchicalStoreException {
 
 		Object value = getOrComputeIfAbsent(namespace, key, defaultCreator);
 		return castToRequiredType(key, value, requiredType);