Support DatabaseInitializerDetector ordering

Update `DatabaseInitializationDependencyConfigurer` so that depends-on
ordering is applied based on the `DatabaseInitializerDetector` order.

Prior to this commit, if multiple DatabaseInitializer beans were
detected the order in which they were initialized was not defined.

See gh-26692

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayMigrationInitializerDatabaseInitializerDetector.java

@@ -34,4 +34,9 @@ class FlywayMigrationInitializerDatabaseInitializerDetector extends AbstractBean
 		return Collections.singleton(FlywayMigrationInitializer.class);
 	}
 
+	@Override
+	public int getOrder() {
+		return 1;
+	}
+
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/sql/init/dependency/DatabaseInitializationDependencyConfigurer.java

@@ -98,10 +98,20 @@ public class DatabaseInitializationDependencyConfigurer implements ImportBeanDef
 			if (initializerBeanNames.isEmpty()) {
 				return;
 			}
+			String previousInitializerBeanName = null;
+			for (String initializerBeanName : initializerBeanNames) {
+				BeanDefinition beanDefinition = getBeanDefinition(initializerBeanName, beanFactory);
+				beanDefinition.setDependsOn(merge(beanDefinition.getDependsOn(), previousInitializerBeanName));
+				previousInitializerBeanName = initializerBeanName;
+			}
 			for (String dependsOnInitializationBeanNames : detectDependsOnInitializationBeanNames(beanFactory)) {
-				BeanDefinition definition = getBeanDefinition(dependsOnInitializationBeanNames, beanFactory);
-				definition.setDependsOn(merge(definition.getDependsOn(), initializerBeanNames));
+				BeanDefinition beanDefinition = getBeanDefinition(dependsOnInitializationBeanNames, beanFactory);
+				beanDefinition.setDependsOn(merge(beanDefinition.getDependsOn(), initializerBeanNames));
+			}
 		}
+
+		private String[] merge(String[] source, String additional) {
+			return merge(source, (additional != null) ? Collections.singleton(additional) : Collections.emptySet());
 		}
 
 		private String[] merge(String[] source, Set<String> additional) {
@@ -112,7 +122,7 @@ public class DatabaseInitializationDependencyConfigurer implements ImportBeanDef
 
 		private Set<String> detectInitializerBeanNames(ConfigurableListableBeanFactory beanFactory) {
 			List<DatabaseInitializerDetector> detectors = getDetectors(beanFactory, DatabaseInitializerDetector.class);
-			Set<String> beanNames = new HashSet<>();
+			Set<String> beanNames = new LinkedHashSet<>();
 			for (DatabaseInitializerDetector detector : detectors) {
 				for (String beanName : detector.detect(beanFactory)) {
 					BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/sql/init/dependency/DatabaseInitializerDetector.java

@@ -21,6 +21,7 @@ import java.util.Set;
 import javax.sql.DataSource;
 
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.core.Ordered;
 
 /**
  * Detects beans that initialize an SQL database. Implementations should be registered in
@@ -30,7 +31,7 @@ import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
  * @author Andy Wilkinson
  * @since 2.5.0
  */
-public interface DatabaseInitializerDetector {
+public interface DatabaseInitializerDetector extends Ordered {
 
 	/**
 	 * Detect beans defined in the given {@code beanFactory} that initialize a
@@ -52,4 +53,9 @@ public interface DatabaseInitializerDetector {
 			Set<String> dataSourceInitializerNames) {
 	}
 
+	@Override
+	default int getOrder() {
+		return 0;
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/sql/init/dependency/DatabaseInitializationDependencyConfigurerTests.java

@@ -40,6 +40,7 @@ import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
+import org.springframework.core.Ordered;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;
 import org.springframework.mock.env.MockEnvironment;
@@ -54,6 +55,7 @@ import static org.mockito.Mockito.verify;
  * Tests for {@link DatabaseInitializationDependencyConfigurer}.
  *
  * @author Andy Wilkinson
+ * @author Phillip Webb
  */
 class DatabaseInitializationDependencyConfigurerTests {
 
@@ -64,7 +66,8 @@ class DatabaseInitializationDependencyConfigurerTests {
 
 	@BeforeEach
 	void resetMocks() {
-		reset(MockDatabaseInitializerDetector.instance, MockedDependsOnDatabaseInitializationDetector.instance);
+		reset(MockDatabaseInitializerDetector.instance, OrderedMockDatabaseInitializerDetector.instance,
+				MockedDependsOnDatabaseInitializationDetector.instance);
 	}
 
 	@Test
@@ -103,6 +106,30 @@ class DatabaseInitializationDependencyConfigurerTests {
 				});
 	}
 
+	@Test
+	void whenDependenciesAreConfiguredDetectedDatabaseInitializersAreInitializedInCorrectOrder() {
+		BeanDefinition alpha = BeanDefinitionBuilder.genericBeanDefinition(String.class).getBeanDefinition();
+		BeanDefinition bravo = BeanDefinitionBuilder.genericBeanDefinition(String.class).getBeanDefinition();
+		BeanDefinition charlie = BeanDefinitionBuilder.genericBeanDefinition(String.class).getBeanDefinition();
+		performDetection(Arrays.asList(MockDatabaseInitializerDetector.class,
+				OrderedMockDatabaseInitializerDetector.class, MockedDependsOnDatabaseInitializationDetector.class),
+				(context) -> {
+					given(MockDatabaseInitializerDetector.instance.detect(context.getBeanFactory()))
+							.willReturn(Collections.singleton("alpha"));
+					given(OrderedMockDatabaseInitializerDetector.instance.detect(context.getBeanFactory()))
+							.willReturn(Collections.singleton("bravo"));
+					given(MockedDependsOnDatabaseInitializationDetector.instance.detect(context.getBeanFactory()))
+							.willReturn(Collections.singleton("charlie"));
+					context.registerBeanDefinition("alpha", alpha);
+					context.registerBeanDefinition("bravo", bravo);
+					context.registerBeanDefinition("charlie", charlie);
+					context.refresh();
+					assertThat(charlie.getDependsOn()).containsExactly("alpha", "bravo");
+					assertThat(bravo.getDependsOn()).containsExactly("alpha");
+					assertThat(alpha.getDependsOn()).isNullOrEmpty();
+				});
+	}
+
 	private void performDetection(Collection<Class<?>> detectors,
 			Consumer<AnnotationConfigApplicationContext> contextCallback) {
 		DetectorSpringFactoriesClassLoader detectorSpringFactories = new DetectorSpringFactoriesClassLoader(this.temp);
@@ -158,7 +185,7 @@ class DatabaseInitializationDependencyConfigurerTests {
 
 		@Override
 		public Set<String> detect(ConfigurableListableBeanFactory beanFactory) {
-			return MockDatabaseInitializerDetector.instance.detect(beanFactory);
+			return instance.detect(beanFactory);
 		}
 
 		@Override
@@ -169,6 +196,22 @@ class DatabaseInitializationDependencyConfigurerTests {
 
 	}
 
+	static class OrderedMockDatabaseInitializerDetector implements DatabaseInitializerDetector {
+
+		private static DatabaseInitializerDetector instance = mock(DatabaseInitializerDetector.class);
+
+		@Override
+		public Set<String> detect(ConfigurableListableBeanFactory beanFactory) {
+			return instance.detect(beanFactory);
+		}
+
+		@Override
+		public int getOrder() {
+			return Ordered.LOWEST_PRECEDENCE;
+		}
+
+	}
+
 	static class MockedDependsOnDatabaseInitializationDetector implements DependsOnDatabaseInitializationDetector {
 
 		private static DependsOnDatabaseInitializationDetector instance = mock(