Make it possible to start without connecting to the database

[AB-xdev]

Fixes #30002

See #30002 (comment) for details

[quarkus-bot]

/cc @gsmet (hibernate-orm)

[yrodiere]

Thanks, but as you can imagine, testing and handling edge cases -- as mentioned in #30002 (comment) -- is actually the most time-consuming part of fixing this.

We'll need someone (you? :) ) to handle that as well.

If you need help, feel free to ping me on https://quarkusio.zulipchat.com/

[yrodiere]

FWIW, regarding this:

I e.g. don't know how I'm supposed to set a config value ("should default to none when asked to start offline") when there is only an interface available...

The interfaces expose configured values to the Quarkus extension, but the extension is free to interpret them before passing values over to Hibernate ORM.

In this case, changing the default would be about:

1. Changing this:

   quarkus/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/HibernateOrmRuntimeConfigPersistenceUnit.java

   Lines 153 to 154 in 18bd561

   	@WithDefault("none")
   	String strategy();

   
   to that:

   // REMOVE @WithDefault!
   Optional<String> strategy();
   

   ... so you can detect that the value is not set.
2. Changing code that calls that method (e.g.

   quarkus/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/FastBootHibernatePersistenceProvider.java

   Lines 415 to 417 in 8029cac

   	runtimeSettingsBuilder.put(AvailableSettings.JAKARTA_HBM2DDL_DATABASE_ACTION,
   	persistenceUnitConfig.database().generation().generation()
   	.orElse(persistenceUnitConfig.schemaManagement().strategy()));

   , but also other places ) so that it adapts the default depending on the value of startOffline, and triggers an exception (io.quarkus.runtime.configuration.ConfigurationException would make sense here, I think?) when the value is set, but conflicts with startOffline.

[AB-xdev]

I think this PR can probably be closed in favor of #48130 which has all/most of the required changes and is done by a Quarkus dev (who is probably knows the code 10x better than me) :)

Anyway thank you for your efforts!

[yrodiere]

Thank you; closing in favor of #48130