update precedence (#215)

also added unit tests, and inline-comments to know which env vars are from which module

Author: duncanista

bottlecap/src/config.rs

@@ -28,24 +28,28 @@ pub struct Config {
     pub version: Option<String>,
     pub tags: Option<String>,
     pub log_level: LogLevel,
-    pub apm_enabled: bool,
     pub serverless_logs_enabled: bool,
-    pub handler: String,
+    pub apm_enabled: bool,
+    pub lambda_handler: String,
 }
 
 impl Default for Config {
     fn default() -> Self {
         Config {
-            apm_enabled: false,
+            // General
             site: "datadoqhq.com".to_string(),
             api_key: String::default(),
+            // Unified Tagging
             env: None,
             service: None,
             version: None,
             tags: None,
+            // Logs
             log_level: LogLevel::default(),
             serverless_logs_enabled: true,
-            handler: String::default(),
+            // APM
+            apm_enabled: false,
+            lambda_handler: String::default(),
         }
     }
 }
@@ -59,14 +63,15 @@ pub enum ConfigError {
 pub fn get_config(config_directory: &Path) -> Result<Config, ConfigError> {
     let path = config_directory.join("datadog.yaml");
     let figment = Figment::new()
-        .merge(Env::prefixed("DD_"))
+        .merge(Yaml::file(path))
         .merge(Env::prefixed("DATADOG_"))
-        .merge(Yaml::file(path));
+        .merge(Env::prefixed("DD_"));
 
     let config = figment.extract().map_err(|err| match err.kind {
         figment::error::Kind::UnknownField(field, _) => ConfigError::UnsupportedField(field),
         _ => ConfigError::ParseError(err.to_string()),
     })?;
+
     Ok(config)
 }
 
@@ -107,6 +112,29 @@ pub mod tests {
         });
     }
 
+    #[test]
+    fn test_precedence() {
+        figment::Jail::expect_with(|jail| {
+            jail.clear_env();
+            jail.create_file(
+                "datadog.yaml",
+                r#"
+                apm_enabled: true
+            "#,
+            )?;
+            jail.set_env("DD_APM_ENABLED", "false");
+            let config = get_config(Path::new("")).expect("should parse config");
+            assert_eq!(
+                config,
+                Config {
+                    apm_enabled: false,
+                    ..Config::default()
+                }
+            );
+            Ok(())
+        });
+    }
+
     #[test]
     fn test_parse_config_file() {
         figment::Jail::expect_with(|jail| {