@ConfigMapping behaviour changed in Quarkus 2.16.2

[luce98]

Describe the bug

We have a project with a configuration as the following in the application.yaml:

quarkus:
  mailer:
    username: ${provider-username}
    password: ${provider-password}

...    

provider:
  username: ${provider-api-username}
  password: ${provider-api-password}

with a .env for the secrets.
Then we have a configuration class as the following:

@ConfigMapping(prefix = "provider")
public interface ProviderProps {

    @NotBlank String username();

    @NotBlank String password();
}

When upgrading one of our projects from Quarkus 2.14.2.Final to 2.16.5.Final, something broke.
After looking at the changelog, I see that smallrye-config was upgraded to 2.13.2, in which is present the following change
smallrye/smallrye-config#881
which I believe it is causing the different behaviour.
I don't expect this to be "fixed" because this is probably a right behaviour but maybe a note could be added in the migration guide to pay attention to name .env variables due to possible conflicts.

Expected behavior

ProviderProps.username() returns the value defined in the .env for provider-api-username.

Actual behavior

ProviderProps.username() returns the value defined in the .env for provider-username.

How to Reproduce?

Clone the repository
/~https://github.com/luce98/quarkus-reproduce-config-issue

1. run the test testConfiguration in class AppConfigTest -> it should pass
2. change quarkus version to 2.16.2
3. run the test again -> it should fail

Output of uname -a or ver

No response

Output of java -version

No response

GraalVM version (if different from Java)

No response

Quarkus version or git rev

2.16.2

Build tool (ie. output of mvnw --version or gradlew --version)

No response

Additional information

No response

[geoand]

cc @radcortez

[radcortez]

I don't expect this to be "fixed" because this is probably a right behaviour but maybe a note could be added in the migration guide to pay attention to name .env variables due to possible conflicts.

Correct. This was a bug, because .env is treated as an Environment Variable source, but it was possible to set properties without the limitations of environment variables. While this was convenient, it also caused issues, since property names would not match the lookup names when performing the lookup name conversion for an Environment Variable.

I've updated the migration guide: /~https://github.com/quarkusio/quarkus/wiki/Migration-Guide-2.16#config

If you still want to use regular property names and external files for configuration, you can use quarkus.config.locations and point it to an external configuration properties files: https://quarkus.io/guides/all-config#quarkus-core_quarkus.config.locations.