jdbc.connections.active and jdbc.connections.idle metrics are not available when using Hikari in a native image

[sdeleuze]

When building https://github.com/spring-projects/spring-petclinic with Spring Boot 4.0.0-SNAPSHOT, I get the following error:

org.graalvm.nativeimage.MissingReflectionRegistrationError: The program tried to reflectively read or write field

   private volatile com.zaxxer.hikari.pool.HikariPool com.zaxxer.hikari.HikariDataSource.pool

This reflective operation seems to be done via DataSourcePoolMetricsAutoConfiguration$DataSourcePoolMetadataMetricsConfiguration$DataSourcePoolMetadataMeterBinder.bindTo -> MeterRegistryPostProcessor.lambda$applyBinders. In DataSourceBuilderRuntimeHints I see a reflective hint for HikariDataSource but not for its pool field.

It works fine with Spring Boot 3.5.3 or Spring Boot 4.0.0-SNAPSHOT with a RuntimeHintsRegistrar performing hints.reflection().registerType(HikariDataSource.class, builder -> builder.withField("pool"));, so maybe Spring Boot 4 should add this reflective hint.

[wilkinsona]

The reflective call is made here. It's been there since we introduced DataSource metrics in Spring Boot 1.2. It's not clear to me what has changed in Spring Boot 4 to cause it to fail now.

[wilkinsona]

With Boot 3.x, the jdbc.connections.active and jdbc.connections.idle metrics are missing. Adding the hint that allows access to the pool field fixes this so I think there was a problem lurking and something has brought it to light.