Make Hikari's pool accessible via reflection in a native image

When it's inaccessible, the jdbc.connections.active and
jdbc.connections.idle metrics are lost.

Closes gh-46214

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/metadata/DataSourcePoolMetadataProvidersConfiguration.java

@@ -24,6 +24,8 @@ import org.apache.commons.dbcp2.BasicDataSource;
 import org.apache.commons.dbcp2.BasicDataSourceMXBean;
 import org.apache.tomcat.jdbc.pool.jmx.ConnectionPoolMBean;
 
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.jdbc.DataSourceUnwrapper;
 import org.springframework.boot.jdbc.metadata.CommonsDbcp2DataSourcePoolMetadata;
@@ -33,6 +35,7 @@ import org.springframework.boot.jdbc.metadata.OracleUcpDataSourcePoolMetadata;
 import org.springframework.boot.jdbc.metadata.TomcatDataSourcePoolMetadata;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.ImportRuntimeHints;
 
 /**
  * Register the {@link DataSourcePoolMetadataProvider} instances for the supported data
@@ -65,6 +68,7 @@ public class DataSourcePoolMetadataProvidersConfiguration {
 
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(HikariDataSource.class)
+	@ImportRuntimeHints(HikariDataSourcePoolMetadataRuntimeHints.class)
 	static class HikariPoolDataSourceMetadataProviderConfiguration {
 
 		@Bean
@@ -116,4 +120,13 @@ public class DataSourcePoolMetadataProvidersConfiguration {
 
 	}
 
+	static class HikariDataSourcePoolMetadataRuntimeHints implements RuntimeHintsRegistrar {
+
+		@Override
+		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+			hints.reflection().registerType(HikariDataSource.class, (builder) -> builder.withField("pool"));
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jdbc/metadata/HikariDataSourcePoolMetadataRuntimeHintsTests.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2012-present 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.autoconfigure.jdbc.metadata;
+
+import java.util.Optional;
+
+import com.zaxxer.hikari.HikariDataSource;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
+import org.springframework.boot.autoconfigure.jdbc.metadata.DataSourcePoolMetadataProvidersConfiguration.HikariDataSourcePoolMetadataRuntimeHints;
+import org.springframework.boot.autoconfigure.jdbc.metadata.DataSourcePoolMetadataProvidersConfiguration.HikariPoolDataSourceMetadataProviderConfiguration;
+import org.springframework.context.annotation.ImportRuntimeHints;
+import org.springframework.core.annotation.MergedAnnotations;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link HikariDataSourcePoolMetadataRuntimeHints}.
+ *
+ * @author Andy Wilkinson
+ */
+class HikariDataSourcePoolMetadataRuntimeHintsTests {
+
+	@Test
+	@SuppressWarnings("rawtypes")
+	void importsRegistrar() {
+		Optional<Class[]> imported = MergedAnnotations.from(HikariPoolDataSourceMetadataProviderConfiguration.class)
+			.get(ImportRuntimeHints.class)
+			.getValue("value", Class[].class);
+		assertThat(imported).hasValue(new Class[] { HikariDataSourcePoolMetadataRuntimeHints.class });
+	}
+
+	@Test
+	void registersHints() {
+		RuntimeHints runtimeHints = new RuntimeHints();
+		new HikariDataSourcePoolMetadataRuntimeHints().registerHints(runtimeHints, getClass().getClassLoader());
+		assertThat(HikariDataSource.class).hasDeclaredFields("pool");
+		assertThat(RuntimeHintsPredicates.reflection().onField(HikariDataSource.class, "pool")).accepts(runtimeHints);
+	}
+
+}