fix: Invalid env var separator on bash

We use `.` as the env var separator in order to differentiate between the prefix
and different levels of the config vs individual config field names
(which would be in UPPER_SNAKE_CASE). However, `.` is not a valid bash
identifier, so we need to use something different.

Switch to using a double underscore (`__`) instead of `.`. This way, we can
support bash and still be able to differentiate between the prefix
and different levels of the config vs individual config field names.

Closes: #219

src/config/app_config.rs

@@ -56,7 +56,7 @@ pub struct AppConfig {
 }
 
 pub const ENV_VAR_PREFIX: &str = "ROADSTER";
-pub const ENV_VAR_SEPARATOR: &str = ".";
+pub const ENV_VAR_SEPARATOR: &str = "__";
 
 impl AppConfig {
     // This runs before tracing is initialized, so we need to use `println` in order to
@@ -86,6 +86,14 @@ impl AppConfig {
                     .convert_case(Case::Kebab)
                     .separator(ENV_VAR_SEPARATOR),
             )
+            // This source is kept for backwards compatibility and may be removed in the next
+            // semver breaking release (0.4+)
+            .add_source(
+                config::Environment::default()
+                    .prefix(ENV_VAR_PREFIX)
+                    .convert_case(Case::Kebab)
+                    .separator("."),
+            )
             .set_override(ENVIRONMENT_ENV_VAR_NAME, environment_str)?
             .build()?;
         let config: AppConfig = config.try_deserialize()?;

src/config/environment.rs

@@ -26,21 +26,32 @@ pub(crate) const ENVIRONMENT_ENV_VAR_NAME: &str = "ENVIRONMENT";
 
 const ENV_VAR_WITH_PREFIX: &str =
     concatcp!(ENV_VAR_PREFIX, ENV_VAR_SEPARATOR, ENVIRONMENT_ENV_VAR_NAME);
+// This env var is used for backwards compatibility and may be removed in the next
+// semver breaking release (0.4+)
+const ENV_VAR_WITH_PREFIX_OLD: &str = concatcp!(ENV_VAR_PREFIX, ".", ENVIRONMENT_ENV_VAR_NAME);
 
 impl Environment {
     // This runs before tracing is initialized, so we need to use `println` in order to
     // log from this method.
     #[allow(clippy::disallowed_macros)]
     pub fn new() -> RoadsterResult<Self> {
         // Get the stage, and validate it by parsing to the Environment enum
-        let environment = env::var(ENV_VAR_WITH_PREFIX)
-            .map_err(|_| anyhow!("Env var `{ENV_VAR_WITH_PREFIX}` not defined."))?;
+        let environment = if let Ok(value) = env::var(ENV_VAR_WITH_PREFIX) {
+            println!("Using environment from `{ENV_VAR_WITH_PREFIX}` env var: {value:?}");
+            value
+        } else if let Ok(value) = env::var(ENV_VAR_WITH_PREFIX_OLD) {
+            // This env var is used for backwards compatibility and may be removed in the next
+            // semver breaking release (0.4+)
+            println!("Using environment from `{ENV_VAR_WITH_PREFIX_OLD}` env var: {value:?}");
+            value
+        } else {
+            Err(anyhow!("Neither `{ENV_VAR_WITH_PREFIX}` nor `{ENV_VAR_WITH_PREFIX_OLD}` env vars are defined."))?;
+            unreachable!()
+        };
         let environment = <Environment as FromStr>::from_str(&environment).map_err(|err| {
-            anyhow!(
-                "Unable to parse `{ENV_VAR_WITH_PREFIX}` env var with value `{environment}`: {err}"
-            )
+            anyhow!("Unable to parse environment from env var value `{environment}`: {err}")
         })?;
-        println!("Using environment from `{ENV_VAR_WITH_PREFIX}` env var: {environment:?}");
+        println!("Parsed environment from env var: {environment:?}");
         Ok(environment)
     }
 }