Fix overriding config vars with underscore from environment

README.md

@@ -231,7 +231,7 @@ into your local `config.hjson` file.
 
 Additionally, you can override any config files with environment variables. These have the same name as the config
 options, and are prefixed with `LEMMY_`. For example, you can override the `database.password` with 
-`LEMMY_DATABASE_PASSWORD=my_password`.
+`LEMMY__DATABASE__POOL_SIZE=10`.
 
 An additional option `LEMMY_DATABASE_URL` is available, which can be used with a PostgreSQL connection string like
 `postgres://lemmy:password@lemmy_db:5432/lemmy`, passing all connection details at once.

server/src/settings.rs

@@ -70,7 +70,10 @@ impl Settings {
 
     // Add in settings from the environment (with a prefix of LEMMY)
     // Eg.. `LEMMY_DEBUG=1 ./target/app` would set the `debug` key
-    s.merge(Environment::with_prefix("LEMMY").separator("_"))?;
+    // Note: we need to use double underscore here, because otherwise variables containing
+    //       underscore cant be set from environmnet.
+    // https://github.com/mehcode/config-rs/issues/73
+    s.merge(Environment::with_prefix("LEMMY").separator("__"))?;
 
     return s.try_into();
   }