Retain default LocalVariableTableParameterNameDiscoverer with warn log entries

For a transition period, LocalVariableTableParameterNameDiscoverer logs a warning for each successful resolution attempt now, suggesting that -parameters was missed.

See gh-29531
See gh-29559

Author: jhoeller

spring-core/src/main/java/org/springframework/core/DefaultParameterNameDiscoverer.java

@@ -18,7 +18,8 @@
 
 /**
  * Default implementation of the {@link ParameterNameDiscoverer} strategy interface,
- * delegating to the Java 8 standard reflection mechanism.
+ * delegating to the Java 8 standard reflection mechanism, with a deprecated fallback
+ * to {@link LocalVariableTableParameterNameDiscoverer}.
  *
  * <p>If a Kotlin reflection implementation is present,
  * {@link KotlinReflectionParameterNameDiscoverer} is added first in the list and
@@ -35,11 +36,20 @@
  */
 public class DefaultParameterNameDiscoverer extends PrioritizedParameterNameDiscoverer {
 
+	@SuppressWarnings("removal")
 	public DefaultParameterNameDiscoverer() {
 		if (KotlinDetector.isKotlinReflectPresent()) {
 			addDiscoverer(new KotlinReflectionParameterNameDiscoverer());
 		}
+
+		// Recommended approach on Java 8+: compilation with -parameters.
 		addDiscoverer(new StandardReflectionParameterNameDiscoverer());
+
+		// Deprecated fallback to class file parsing for -debug symbols.
+		// Does not work on native images without class file resources.
+		if (!NativeDetector.inNativeImage()) {
+			addDiscoverer(new LocalVariableTableParameterNameDiscoverer());
+		}
 	}
 
 }

spring-core/src/main/java/org/springframework/core/LocalVariableTableParameterNameDiscoverer.java

@@ -56,7 +56,7 @@
  * @deprecated as of 6.0.1, in favor of {@link StandardReflectionParameterNameDiscoverer}
  * (with the "-parameters" compiler flag)
  */
-@Deprecated(since = "6.0.1")
+@Deprecated(since = "6.0.1", forRemoval = true)
 public class LocalVariableTableParameterNameDiscoverer implements ParameterNameDiscoverer {
 
 	private static final Log logger = LogFactory.getLog(LocalVariableTableParameterNameDiscoverer.class);
@@ -85,7 +85,12 @@ public String[] getParameterNames(Constructor<?> ctor) {
 	private String[] doGetParameterNames(Executable executable) {
 		Class<?> declaringClass = executable.getDeclaringClass();
 		Map<Executable, String[]> map = this.parameterNamesCache.computeIfAbsent(declaringClass, this::inspectClass);
-		return (map != NO_DEBUG_INFO_MAP ? map.get(executable) : null);
+		String[] names = (map != NO_DEBUG_INFO_MAP ? map.get(executable) : null);
+		if (names != null && logger.isWarnEnabled()) {
+			logger.warn("Using deprecated '-debug' fallback for parameter name resolution. " +
+					"Compile the affected code with '-parameters' instead: " + executable);
+		}
+		return names;
 	}
 
 	/**

spring-core/src/main/java/org/springframework/core/ReactiveAdapterRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -339,11 +339,7 @@ void registerAdapters(ReactiveAdapterRegistry registry) {
 
 	/**
 	 * {@code BlockHoundIntegration} for spring-core classes.
-	 * <p>Explicitly allow the following:
-	 * <ul>
-	 * <li>Reading class info via {@link LocalVariableTableParameterNameDiscoverer}.
-	 * <li>Locking within {@link ConcurrentReferenceHashMap}.
-	 * </ul>
+	 * Explicitly allows locking within {@link ConcurrentReferenceHashMap}.
 	 * @since 5.2.4
 	 */
 	public static class SpringCoreBlockHoundIntegration implements BlockHoundIntegration {
@@ -352,9 +348,6 @@ public static class SpringCoreBlockHoundIntegration implements BlockHoundIntegra
 		public void applyTo(BlockHound.Builder builder) {
 			// Avoid hard references potentially anywhere in spring-core (no need for structural dependency)
 
-			builder.allowBlockingCallsInside(
-					"org.springframework.core.LocalVariableTableParameterNameDiscoverer", "inspectClass");
-
 			String className = "org.springframework.util.ConcurrentReferenceHashMap$Segment";
 			builder.allowBlockingCallsInside(className, "doTask");
 			builder.allowBlockingCallsInside(className, "clear");

spring-core/src/test/java/org/springframework/core/LocalVariableTableParameterNameDiscovererTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,7 +34,8 @@
  */
 class LocalVariableTableParameterNameDiscovererTests {
 
-	private final LocalVariableTableParameterNameDiscoverer discoverer = new LocalVariableTableParameterNameDiscoverer();
+	@SuppressWarnings("removal")
+	private final ParameterNameDiscoverer discoverer = new LocalVariableTableParameterNameDiscoverer();
 
 
 	@Test

spring-core/src/test/java/org/springframework/core/SpringCoreBlockHoundIntegrationTests.java

@@ -16,7 +16,6 @@
 
 package org.springframework.core;
 
-import java.lang.reflect.Method;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 
@@ -28,7 +27,6 @@
 import reactor.core.scheduler.ReactorBlockHoundIntegration;
 import reactor.core.scheduler.Schedulers;
 
-import org.springframework.tests.sample.objects.TestObject;
 import org.springframework.util.ConcurrentReferenceHashMap;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -52,11 +50,10 @@
 @DisabledOnJre(value= {JRE.JAVA_18, JRE.JAVA_19}, disabledReason = "BlockHound is not compatible with Java 18+")
 class SpringCoreBlockHoundIntegrationTests {
 
-
 	@BeforeAll
-	static void setUp() {
+	static void setup() {
 		BlockHound.builder()
-				.with(new ReactorBlockHoundIntegration()) // Reactor non-blocking thread predicate
+				.with(new ReactorBlockHoundIntegration())  // Reactor non-blocking thread predicate
 				.with(new ReactiveAdapterRegistry.SpringCoreBlockHoundIntegration())
 				.install();
 	}
@@ -68,15 +65,6 @@ void blockHoundIsInstalled() {
 				.hasMessageContaining("Blocking call!");
 	}
 
-	@Test
-	void localVariableTableParameterNameDiscoverer() {
-		testNonBlockingTask(() -> {
-			Method setName = TestObject.class.getMethod("setName", String.class);
-			String[] names = new LocalVariableTableParameterNameDiscoverer().getParameterNames(setName);
-			assertThat(names).containsExactly("name");
-		});
-	}
-
 	@Test
 	void concurrentReferenceHashMap() {
 		int size = 10000;