Include throwables from Logback errors when reporting invalid config

Closes gh-32562

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java

@@ -167,17 +167,30 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 		catch (Exception ex) {
 			throw new IllegalStateException("Could not initialize Logback logging from " + location, ex);
 		}
-		List<Status> statuses = loggerContext.getStatusManager().getCopyOfStatusList();
+		reportConfigurationErrorsIfNecessary(loggerContext);
+	}
+
+	private void reportConfigurationErrorsIfNecessary(LoggerContext loggerContext) {
 		StringBuilder errors = new StringBuilder();
-		for (Status status : statuses) {
+		List<Throwable> suppressedExceptions = new ArrayList<>();
+		for (Status status : loggerContext.getStatusManager().getCopyOfStatusList()) {
 			if (status.getLevel() == Status.ERROR) {
 				errors.append((errors.length() > 0) ? String.format("%n") : "");
 				errors.append(status.toString());
+				if (status.getThrowable() != null) {
+					suppressedExceptions.add(status.getThrowable());
+				}
 			}
 		}
-		if (errors.length() > 0) {
-			throw new IllegalStateException(String.format("Logback configuration error detected: %n%s", errors));
+		if (errors.length() == 0) {
+			return;
+		}
+		IllegalStateException ex = new IllegalStateException(
+				String.format("Logback configuration error detected: %n%s", errors));
+		for (Throwable suppressedException : suppressedExceptions) {
+			ex.addSuppressed(suppressedException);
 		}
+		throw ex;
 	}
 
 	private void configureByResourceUrl(LoggingInitializationContext initializationContext, LoggerContext loggerContext,

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/logback/LogbackLoggingSystemTests.java

@@ -38,6 +38,7 @@ import ch.qos.logback.core.ConsoleAppender;
 import ch.qos.logback.core.encoder.LayoutWrappingEncoder;
 import ch.qos.logback.core.rolling.RollingFileAppender;
 import ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy;
+import ch.qos.logback.core.util.DynamicClassLoadingException;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -519,7 +520,7 @@ class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 		initialize(this.initializationContext, null, null);
 		LoggerContext loggerContext = (LoggerContext) StaticLoggerBinder.getSingleton().getLoggerFactory();
 		Map<String, String> properties = loggerContext.getCopyOfPropertyMap();
-		Set<String> expectedProperties = new HashSet<String>();
+		Set<String> expectedProperties = new HashSet<>();
 		ReflectionUtils.doWithFields(LogbackLoggingSystemProperties.class,
 				(field) -> expectedProperties.add((String) field.get(null)), this::isPublicStaticFinal);
 		expectedProperties.removeAll(Arrays.asList("LOG_FILE", "LOG_PATH"));
@@ -624,6 +625,16 @@ class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 		assertThat(encoder.getCharset()).isEqualTo(StandardCharsets.UTF_16);
 	}
 
+	@Test
+	void whenConfigurationErrorIsDetectedUnderlyingCausesAreIncludedAsSuppressedExceptions() {
+		this.loggingSystem.beforeInitialize();
+		assertThatIllegalStateException()
+			.isThrownBy(() -> initialize(this.initializationContext, "classpath:logback-broken.xml",
+					getLogFile(tmpDir() + "/tmp.log", null)))
+			.satisfies((ex) -> assertThat(ex.getSuppressed())
+				.hasAtLeastOneElementOfType(DynamicClassLoadingException.class));
+	}
+
 	private void initialize(LoggingInitializationContext context, String configLocation, LogFile logFile) {
 		this.loggingSystem.getSystemProperties((ConfigurableEnvironment) context.getEnvironment()).apply(logFile);
 		this.loggingSystem.initialize(context, configLocation, logFile);