Make creating LauncherSessionListeners interceptable

Author: marcphilipp

junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherInterceptor.java

@@ -11,6 +11,9 @@
 package org.junit.platform.launcher;
 
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.INTERNAL;
+
+import java.util.List;
 
 import org.apiguardian.api.API;
 
@@ -28,6 +31,18 @@
 @API(status = EXPERIMENTAL, since = "1.10")
 public interface LauncherInterceptor {
 
+	LauncherInterceptor NOOP = new LauncherInterceptor() {
+		@Override
+		public <T> T intercept(Invocation<T> invocation) {
+			return invocation.proceed();
+		}
+
+		@Override
+		public void close() {
+			// do nothing
+		}
+	};
+
 	/**
 	 * Intercept the supplied invocation.
 	 *
@@ -54,4 +69,29 @@ public interface LauncherInterceptor {
 	interface Invocation<T> {
 		T proceed();
 	}
+
+	@API(status = INTERNAL, since = "1.10")
+	static LauncherInterceptor composite(List<LauncherInterceptor> interceptors) {
+		if (interceptors.isEmpty()) {
+			return NOOP;
+		}
+		return interceptors.stream() //
+				.skip(1) //
+				.reduce(interceptors.get(0), (a, b) -> new LauncherInterceptor() {
+					@Override
+					public void close() {
+						try {
+							a.close();
+						}
+						finally {
+							b.close();
+						}
+					}
+
+					@Override
+					public <T> T intercept(Invocation<T> invocation) {
+						return a.intercept(() -> b.intercept(invocation));
+					}
+				});
+	}
 }

junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultLauncherSession.java

@@ -33,8 +33,10 @@ class DefaultLauncherSession implements LauncherSession {
 
 	DefaultLauncherSession(List<LauncherInterceptor> interceptors, Supplier<Launcher> launcherSupplier,
 			Supplier<LauncherSessionListener> listenerSupplier) {
-		this.listener = listenerSupplier.get();
-		CloseableLauncher closeableLauncher = InterceptingClosableLauncher.decorate(launcherSupplier, interceptors);
+		LauncherInterceptor interceptor = LauncherInterceptor.composite(interceptors);
+		this.listener = interceptor.intercept(listenerSupplier::get);
+		Launcher launcher = interceptor.intercept(launcherSupplier::get);
+		CloseableLauncher closeableLauncher = new InterceptingClosableLauncher(launcher, interceptor);
 		this.launcher = new DelegatingCloseableLauncher<>(closeableLauncher, delegate -> {
 			delegate.close();
 			return ClosedLauncher.INSTANCE;

junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InterceptingClosableLauncher.java

@@ -10,12 +10,6 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.function.Function.identity;
-
-import java.util.List;
-import java.util.Optional;
-import java.util.function.Supplier;
-
 import org.junit.platform.launcher.Launcher;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
 import org.junit.platform.launcher.LauncherInterceptor;
@@ -27,42 +21,9 @@
  */
 class InterceptingClosableLauncher extends DelegatingCloseableLauncher<Launcher> {
 
-	static CloseableLauncher decorate(Supplier<Launcher> launcherSupplier, List<LauncherInterceptor> interceptors) {
-		Optional<LauncherInterceptor> combinedInterceptor = composite(interceptors);
-		Launcher launcher = combinedInterceptor.map(it -> it.intercept(launcherSupplier::get)).orElseGet(
-			launcherSupplier);
-		return combinedInterceptor //
-				.map(it -> (CloseableLauncher) new InterceptingClosableLauncher(launcher, it)) //
-				.orElse(new DelegatingCloseableLauncher<>(launcher, identity()));
-	}
-
-	private static Optional<LauncherInterceptor> composite(List<LauncherInterceptor> interceptors) {
-		if (interceptors.isEmpty()) {
-			return Optional.empty();
-		}
-		return Optional.of(interceptors.stream() //
-				.skip(1) //
-				.reduce(interceptors.get(0), (a, b) -> new LauncherInterceptor() {
-					@Override
-					public void close() {
-						try {
-							a.close();
-						}
-						finally {
-							b.close();
-						}
-					}
-
-					@Override
-					public <T> T intercept(Invocation<T> invocation) {
-						return a.intercept(() -> b.intercept(invocation));
-					}
-				}));
-	}
-
 	private final LauncherInterceptor interceptor;
 
-	private InterceptingClosableLauncher(Launcher delegate, LauncherInterceptor interceptor) {
+	InterceptingClosableLauncher(Launcher delegate, LauncherInterceptor interceptor) {
 		super(delegate, it -> {
 			interceptor.close();
 			return it;