Warning to detect self referencing environment variable

Hey i like the ${VAR} syntax in environment variables

But i think there is a feature that can be helpful needed, detecting self referencing variable

For example, when you deploy a redis from database option, it will pre-populate REDIS_HOST REDIS_PORT etc, as shared environment var in a project

Then, if you have service like web, Its quite natural if you put REDIS_HOST REDIS_PORT as env var in your web service

I tried to use REDIS_HOST=${REDIS_HOST} i thought it gonna populate REDIS_HOST with the REDIS_HOST var from my redis instance, but it returns NaN. I was confused at first but it turns out after making exposing variable like SHARED_REDIS_HOST, it works

Maybe add a warning if we use self referencing variable?