Convention for optionally inferring configuration values

[iocanel]

Description

Every know and then I come accross the case of having an Optional configuration property that the user is expected to provide and a secondary boolean flag that pretty much tells Quarkus to try and infer the value of the Optional property.

Recent example comming from: #33437:

    /**
     * The gRPC port to use for the probe (the format is either port or port:service).
     */
    @ConfigItem
    Optional<String> grpcAction;

    /**
     * If enabled and `grpc-action` is not provided, it will use the generated service name and the gRPC port.
     */
    @ConfigItem(defaultValue = "false")
    boolean grpcActionEnabled;

In the example above:

• If user specified nothing no grpcAction gets exposed.
• If user specifies grpcAction it's used as is.
• if user specifies grpcActionEnabled then grpcAction gets inferred.

I would like to propose an alternative for such cases, that is having a value like: <auto> to signify that the property is meant to be automatically configured. Of course for this change to be meaningfull it needs to be widely applied.

Thought's?

Implementation ideas

No response

[iocanel]

I experimented a little bit with it in order to find an elegant solution.

The goal of these experiments was to find a safe way of adopting conventions like the one described.
I didn't manage to find a proper solution but here are some things I've tried and the limitation of each approach.
I am putting my findings here for future reference.

For all the described approaches the end goal was to be able to dfined properties like this:

quarkus.kubernetes.readiness-probe.grpc-action.auto = true
quarkus.kubernetes.readiness-probe.grpc-action = someservice:9999

In other words instead of defining multiple properties at the same level to have some sort of optional fields under the same property to influence the behavior.

ConfigGroup + Converter

quarkus.kubernetes.readiness-probe.grpc-action is not recognized as a valid key.

EnumMap + Converter

• EnumMap does not seem to be recognized as Map (I think this goes for all types extending Map, but not 100% sure).
• Only String keys are supported.

Map + Converter

• can't restrict keys.
• quarkus.kubernetes.readiness-probe.grpc-action is not recognized as a valid key.