Don't detect main method from launcher classes

Update `MainMethod` discovery so that launcher classes from the
`org.springframework.boot.loader` code are not considered. This restores
the behavior of Spring Boot 2.7.11 and allows remote restart of uber
jars without pulling the loader classes into the `RestartClassLoader`.

Fixes gh-39733

Author: philwebb

Diff for: spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/MainMethod.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -43,7 +43,7 @@ private Method getMainMethod(Thread thread) {
 		StackTraceElement[] stackTrace = thread.getStackTrace();
 		for (int i = stackTrace.length - 1; i >= 0; i--) {
 			StackTraceElement element = stackTrace[i];
-			if ("main".equals(element.getMethodName())) {
+			if ("main".equals(element.getMethodName()) && !isLoaderClass(element.getClassName())) {
 				Method method = getMainMethod(element);
 				if (method != null) {
 					return method;
@@ -53,6 +53,10 @@ private Method getMainMethod(Thread thread) {
 		throw new IllegalStateException("Unable to find main method");
 	}
 
+	private boolean isLoaderClass(String className) {
+		return className.startsWith("org.springframework.boot.loader.");
+	}
+
 	private Method getMainMethod(StackTraceElement element) {
 		try {
 			Class<?> elementClass = Class.forName(element.getClassName());

Diff for: spring-boot-project/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/MainMethodTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -21,6 +21,7 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.boot.loader.launch.FakeJarLauncher;
 import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -64,6 +65,15 @@ void nestedMainMethod() throws Exception {
 		assertThat(method.getDeclaringClassName()).isEqualTo(nestedMain.getDeclaringClass().getName());
 	}
 
+	@Test // gh-39733
+	void vaiJarLauncher() throws Exception {
+		FakeJarLauncher.action = (args) -> Valid.main(args);
+		MainMethod method = new TestThread(FakeJarLauncher::main).test();
+		Method expectedMain = Valid.class.getMethod("main", String[].class);
+		assertThat(method.getMethod()).isEqualTo(expectedMain);
+		assertThat(method.getDeclaringClassName()).isEqualTo(expectedMain.getDeclaringClass().getName());
+	}
+
 	@Test
 	void missingArgsMainMethod() {
 		assertThatIllegalStateException().isThrownBy(() -> new TestThread(MissingArgs::main).test())

Diff for: spring-boot-project/spring-boot-devtools/src/test/java/org/springframework/boot/loader/launch/FakeJarLauncher.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.loader.launch;
+
+import java.util.function.Consumer;
+
+/**
+ * Fake launcher in the {@code org.springframework.boot.loader.launch} package used in
+ * {@code MainMethodTests}.
+ *
+ * @author Phillip Webb
+ */
+public final class FakeJarLauncher {
+
+	public static Consumer<String[]> action;
+
+	private FakeJarLauncher() {
+	}
+
+	public static void main(String... args) {
+		action.accept(args);
+	}
+
+}