Behaviour of Environment config source is not explicit

The spec mentions that environment variables can be used as config sources. It does not specify if those variables need to be converted to a different format. From how I understood @Emily-Jiang an env variable of MP_METRICS_TAGS should be the same as a config key of mp.metrics.tags that was passed in via e.g. a system property.

cc @jmesnil

[jmesnil]

Another alternative could be to change the type of the @ConfigProperty’s name to be String[] instead of String:

public @interface ConfigProperty {
    String[] name() default "";
}

With that change, we can specify either no name, a single name or an array of names (that would solve heiko’s issue):

@Inject
@ConfigProperty(name={"MP_METRICS_TAGS", "mp.metrics.tags"})
String tags;

The advantage is that we keep a single @ConfigProperty annotation to configure a property. There is only 1 defaultValue, the names of the properties are ordered.

And afaict, we do not break existing user code, the code below is still valid:

@Inject
@ConfigProperty(name="my.double.property")
private double doubleProperty;

@Inject
// config property names is inferred from the injection point
@ConfigProperty
private int intProperty;

@Emily-Jiang wdyt?

[jmesnil]

+1 making the @ConfigProperty repeatable is a good idea.

The spec should also clarify how default value interact with repeated @ConfigProperty:

• @ConfigProperty are searched in the order of the annotations.
• The first @ConfigProperty that defines a value or a default value will be used.

In practice, this means that only the last @ConfigProperty should have a default value otherwise all subsequent ones would not be searched.

wdyt?