`strict()` mode fails because of the environment variables.

[jhoarau-grindr]

strict() mode fails because of the environment variables.

Test case:

class CreateConfigTest : FunSpec({

   data class TestConfig(
      val name: String,
   )

   test("strict() should ignore environment variables") {
      val config = ConfigLoaderBuilder.default()
         .addMapSource(mapOf("name" to "test"))
         .strict()
         .build()
         .loadConfigOrThrow<TestConfig>()

      config.name shouldBe "test"
   }
})

Expected output:

Test should pass

Actual output:

Test fails with error:

Error loading config because:
com.sksamuel.hoplite.ConfigException: Error loading config because:

    Config value '' at (env) was unused

    Config value '_' at (env) was unused

    ... (Cut for brevity)

    Config value 'USER' at (env) was unused

    Config value 'ZSH' at (env) was unused

    Config value 'TMPDIR' at (env) was unused

    Config value 'PYENV' at (env) was unused

    Config value 'PYENV_SHELL' at (env) was unused

    Config value 'PYENV_ROOT' at (env) was unused

    Config value 'LC' at (env) was unused

    Config value 'LC_CTYPE' at (env) was unused

    Config value 'LESS' at (env) was unused

    Config value 'HOME' at (env) was unused
	at com.sksamuel.hoplite.ConfigLoaderKt$returnOrThrow$1.invoke(ConfigLoader.kt:354)
	at com.sksamuel.hoplite.ConfigLoaderKt$returnOrThrow$1.invoke(ConfigLoader.kt:351)
	at com.sksamuel.hoplite.fp.ValidatedKt.getOrElse(Validated.kt:115)
	at com.sksamuel.hoplite.ConfigLoaderKt.returnOrThrow(ConfigLoader.kt:351)
	at com.sksamuel.hoplite.ConfigLoader.returnOrThrow(ConfigLoader.kt:312)
	at com.grindr.accelerator.app.CreateConfigTest$1$1.invokeSuspend(CreateConfigTest.kt:31)
	at com.grindr.accelerator.app.CreateConfigTest$1$1.invoke(CreateConfigTest.kt)
	at com.grindr.accelerator.app.CreateConfigTest$1$1.invoke(CreateConfigTest.kt)

[rocketraman]

Thoughts from discussion with @sksamuel in Slack:

Three use cases for strict

1. people who don't care about strict
2. people who want to find stale values in their yaml/json config files (that's the main use case I think)
3. people who wanna be super buttoned up and check everything

For the second case, strict mode does not need to fail because of the environment variable processor.

However, for the third case, it does. Consider restricted environments where the environment is tightly controlled, such as within systemd units or docker/podman containers.

However, even in the third case, the environment will likely contain values that are not used by Hoplite (consider a Kubernetes container), so all of this suggests that a processor like the env var processor should be able to be configured in terms of how it deals with strict mode e.g. do not fail on unused env vars (case 2), or ignore specific unused env vars, but fail on other unused env vars (case 3).

[TwoClocks]

I'm definitely in the No2 camp. Operators setting configuration that the code is no longer using should fail fast.

I think the subtly is what does "used" mean? In HOCON files I can set datahost: "10.0.1.13", and use it all over the place as databaseIp: ${datahost}, but the datahost value itself never makes it into a data class. I would argue it is used if it's referenced by something that ends up in data class. But strict() should fail if it's not referenced, or referenced by something that is not used.