Add exception and failure analyzer for missing AOT initializer

The diagnostics text include the name of the AOT initializer class and
the main class name. It also tells the user how to switch of the AOT
mode.

Closes gh-38645

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/AotInitializerNotFoundException.java

@@ -0,0 +1,39 @@
+/*
+ * 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;
+
+/**
+ * Exception thrown when the AOT initializer couldn't be found.
+ *
+ * @author Moritz Halbritter
+ * @since 3.2.6
+ */
+public class AotInitializerNotFoundException extends RuntimeException {
+
+	private final Class<?> mainClass;
+
+	public AotInitializerNotFoundException(Class<?> mainClass, String initializerClassName) {
+		super("Startup with AOT mode enabled failed: AOT initializer %s could not be found"
+			.formatted(initializerClassName));
+		this.mainClass = mainClass;
+	}
+
+	public Class<?> getMainClass() {
+		return this.mainClass;
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -439,10 +439,9 @@ public class SpringApplication {
 					initializers.stream().filter(AotApplicationContextInitializer.class::isInstance).toList());
 			if (aotInitializers.isEmpty()) {
 				String initializerClassName = this.mainApplicationClass.getName() + "__ApplicationContextInitializer";
-				Assert.state(ClassUtils.isPresent(initializerClassName, getClassLoader()),
-						"You are starting the application with AOT mode enabled but AOT processing hasn't happened. "
-								+ "Please build your application with enabled AOT processing first, "
-								+ "or remove the system property 'spring.aot.enabled' to run the application in regular mode");
+				if (!ClassUtils.isPresent(initializerClassName, getClassLoader())) {
+					throw new AotInitializerNotFoundException(this.mainApplicationClass, initializerClassName);
+				}
 				aotInitializers.add(AotApplicationContextInitializer.forInitializerClasses(initializerClassName));
 			}
 			initializers.removeAll(aotInitializers);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/AotInitializerNotFoundFailureAnalyzer.java

@@ -0,0 +1,40 @@
+/*
+ * 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.diagnostics.analyzer;
+
+import org.springframework.boot.AotInitializerNotFoundException;
+import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
+import org.springframework.boot.diagnostics.FailureAnalysis;
+
+/**
+ * An {@link AbstractFailureAnalyzer} that performs analysis of failures caused by a
+ * {@link AotInitializerNotFoundException}.
+ *
+ * @author Moritz Halbritter
+ */
+class AotInitializerNotFoundFailureAnalyzer extends AbstractFailureAnalyzer<AotInitializerNotFoundException> {
+
+	@Override
+	protected FailureAnalysis analyze(Throwable rootFailure, AotInitializerNotFoundException cause) {
+		return new FailureAnalysis(cause.getMessage(), "Consider the following:\n"
+				+ "\tDid you build the application with enabled AOT processing?\n"
+				+ "\tIs the main class %s correct?\n".formatted(cause.getMainClass().getName())
+				+ "\tIf you want to run the application in regular mode, remove the system property 'spring.aot.enabled'",
+				cause);
+	}
+
+}

spring-boot-project/spring-boot/src/main/resources/META-INF/spring.factories

@@ -64,6 +64,7 @@ org.springframework.boot.diagnostics.FailureAnalyzer=\
 org.springframework.boot.context.config.ConfigDataNotFoundFailureAnalyzer,\
 org.springframework.boot.context.properties.IncompatibleConfigurationFailureAnalyzer,\
 org.springframework.boot.context.properties.NotConstructorBoundInjectionFailureAnalyzer,\
+org.springframework.boot.diagnostics.analyzer.AotInitializerNotFoundFailureAnalyzer,\
 org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
 org.springframework.boot.diagnostics.analyzer.BeanDefinitionOverrideFailureAnalyzer,\
 org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java

@@ -1445,8 +1445,8 @@ class SpringApplicationTests {
 		application.setMainApplicationClass(TestSpringApplication.class);
 		System.setProperty(AotDetector.AOT_ENABLED, "true");
 		try {
-			assertThatIllegalStateException().isThrownBy(application::run)
-				.withMessageContaining("but AOT processing hasn't happened");
+			assertThatExceptionOfType(AotInitializerNotFoundException.class).isThrownBy(application::run)
+				.withMessageMatching("^.+AOT initializer .+ could not be found$");
 		}
 		finally {
 			System.clearProperty(AotDetector.AOT_ENABLED);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/AotInitializerNotFoundFailureAnalyzerTests.java

@@ -0,0 +1,52 @@
+/*
+ * 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.diagnostics.analyzer;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.AotInitializerNotFoundException;
+import org.springframework.boot.diagnostics.FailureAnalysis;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link AotInitializerNotFoundFailureAnalyzer}.
+ *
+ * @author Moritz Halbritter
+ */
+class AotInitializerNotFoundFailureAnalyzerTests {
+
+	@Test
+	void shouldAnalyze() {
+		FailureAnalysis analysis = analyze();
+		assertThat(analysis.getDescription()).isEqualTo(
+				"Startup with AOT mode enabled failed: AOT initializer class org.springframework.boot.diagnostics.analyzer.AotInitializerNotFoundFailureAnalyzerTests__ApplicationContextInitializer could not be found");
+		assertThat(analysis.getAction()).isEqualTo(
+				"""
+						Consider the following:
+						\tDid you build the application with enabled AOT processing?
+						\tIs the main class org.springframework.boot.diagnostics.analyzer.AotInitializerNotFoundFailureAnalyzerTests correct?
+						\tIf you want to run the application in regular mode, remove the system property 'spring.aot.enabled'""");
+	}
+
+	private FailureAnalysis analyze() {
+		return new AotInitializerNotFoundFailureAnalyzer()
+			.analyze(new AotInitializerNotFoundException(AotInitializerNotFoundFailureAnalyzerTests.class,
+					AotInitializerNotFoundFailureAnalyzerTests.class + "__ApplicationContextInitializer"));
+	}
+
+}