Environment variables in HOCON files will not be resolved in some cases

[luedi]

I'm using the standard Kotlin application.conf behavior to use environment variables to override config values. So my HOCON file looks like this (simplified):

{
  prod = {
    host = "myprodhost:myport"
    host = ${?FIXED_PREFIX_MY_PROD_HOST}
  }
  dev = {
    host = "mydevhost:mydevport"
    host = ${?FIXED_PREFIX_MY_DEV_HOST}
  }
  anotherProperty = "stage_independent"
  anotherProperty = ${?FIXED_PREFIX_ANOTHER_PROPE>RTY}
}

Then I implemented a configuration class which is (very simplified) like this:

enum class Stage {
    DEV,
    PROD
}

// this interface is needed to be able to process the configuration
sealed interface Configuration

data class StageConfig(
    val host: String,
) : Configuration

object HostConfiguration {

    data class HostConfig(
        val stages: Map<Stage, StageConfig>,
        val anotherProperty: String,
    )

    private val hostConfig: HostConfig

    init {
        // by the way: how can i avoid this and read the nested configuration direct into HostConfig???
        data class InternalHostConfig(
            val prod: Configuration,
            val dev: Configuration,
            val anotherProperty: String,
        )

        val config = ConfigLoaderBuilder.default()
            .addPropertySource(PropertySource.resource("/host.conf"))
            .build()
            .loadConfigOrThrow<InternalHostConfig>()

        hostConfig = HostConfig(
            mapOf(
                Stage.PROD to (config.prod as StageConfig),
                Stage.DEV to (config.dev as StageConfig)
            ),
            config.anoherProperty,
        )
    }

    fun stageConfig(stage: Stage): StageConfig = hostConfig.stages[stage]!!

    fun anotherProperty() = hostConfig.anotherProperty
}

At least I wrote some unit tests for my configuration with the aid of Kotest. Kotest has a feature to inject environment variables into a test (which works fine). This tests runs successful when starting them from the IntelliJ editor pane but are failing when running them in a Gradle build or with the Kotest runner. In this cases config.host contains "myprodhost:myport". Here is the, again very simpolified code:

class HostConfigurationKtTest : FunSpec({

    test("Environment variables should be used when present") {
        withEnvironment(
            mapof(
                "FIXED_PREFIX_MY_PROD_HOST" to "host_url_prod",
            )
        ) {
            // This is successful
            System.getenv("FIXED_PREFIX_MY_PROD_HOST") shouldBe "host_url_prod"

            val prodConfig = HostConfiguration.stageConfig(Stage.PROD)
            // This will fail
            prodConfig.host shouldBe "broker_url_prod"
        }
    }
})

I've read about the EnvironmentVariablesOverridePropertySource but i can't prefix environment variables with config.override. In our production environment the environment variables are generated by a tool which follows a specific naming convention which i can't override. For example, if i declare a variable MY_HOST in the tool, a prefix FIXED_PREFIX is automatically added.

Interesting, when I change my code like you do in the EnvironmentVariablesOverridePropertySourceTest the test fails always.

I used hopelite because my real configuration is much more complicated and the library helps me to save a lot of work in opposite to use the standard application.conf.

Before I forget, my environment is:

IntelliJ IDEA Ultimate 2023.3
Kotlin 1.9.21 targeting Java 21
Kotest 5.8.0
hopelite 2.7.5