Config overhaul: make some fields mandatory

src/config/mod.rs

@@ -222,6 +222,9 @@ pub enum Error {
 
     #[error("Unsupported configuration version: {version}")]
     UnsupportedVersion { version: Version },
+
+    #[error("Missing mandatory configuration option. Option path: {path}")]
+    MissingMandatoryOption { path: String },
 }
 
 impl From<figment::Error> for Error {
@@ -295,26 +298,28 @@ impl Configuration {
     /// Loads the settings from the `Info` struct. The whole
     /// configuration in toml format is included in the `info.index_toml` string.
     ///
-    /// Optionally will override the:
-    ///
-    /// - Tracker api token.
-    /// - The auth secret key.
+    /// Configuration provided via env var has priority over config file path.
     ///
     /// # Errors
     ///
     /// Will return `Err` if the environment variable does not exist or has a bad configuration.
     pub fn load_settings(info: &Info) -> Result<Settings, Error> {
+        // Load configuration provided by the user, prioritizing env vars
         let figment = if let Some(config_toml) = &info.config_toml {
             // Config in env var has priority over config file path
-            Figment::from(Serialized::defaults(Settings::default()))
-                .merge(Toml::string(config_toml))
-                .merge(Env::prefixed(CONFIG_OVERRIDE_PREFIX).split(CONFIG_OVERRIDE_SEPARATOR))
+            Figment::from(Toml::string(config_toml)).merge(Env::prefixed(CONFIG_OVERRIDE_PREFIX).split(CONFIG_OVERRIDE_SEPARATOR))
         } else {
-            Figment::from(Serialized::defaults(Settings::default()))
-                .merge(Toml::file(&info.config_toml_path))
+            Figment::from(Toml::file(&info.config_toml_path))
                 .merge(Env::prefixed(CONFIG_OVERRIDE_PREFIX).split(CONFIG_OVERRIDE_SEPARATOR))
         };
 
+        // Make sure user has provided the mandatory options.
+        Self::check_mandatory_options(&figment)?;
+
+        // Fill missing options with default values.
+        let figment = figment.join(Serialized::defaults(Settings::default()));
+
+        // Build final configuration.
         let settings: Settings = figment.extract()?;
 
         if settings.metadata.schema_version != Version::new(VERSION_2) {
@@ -326,6 +331,28 @@ impl Configuration {
         Ok(settings)
     }
 
+    /// Some configuration options are mandatory. The tracker will panic if
+    /// the user doesn't provide an explicit value for them from one of the
+    /// configuration sources: TOML or ENV VARS.
+    ///
+    /// # Errors
+    ///
+    /// Will return an error if a mandatory configuration option is only
+    /// obtained by default value (code), meaning the user hasn't overridden it.
+    fn check_mandatory_options(figment: &Figment) -> Result<(), Error> {
+        let mandatory_options = ["metadata.schema_version", "logging.threshold"];
+
+        for mandatory_option in mandatory_options {
+            figment
+                .find_value(mandatory_option)
+                .map_err(|_err| Error::MissingMandatoryOption {
+                    path: mandatory_option.to_owned(),
+                })?;
+        }
+
+        Ok(())
+    }
+
     pub async fn get_all(&self) -> Settings {
         let settings_lock = self.settings.read().await;
 
@@ -474,6 +501,58 @@ mod tests {
         });
     }
 
+    #[test]
+    fn configuration_should_use_the_default_values_when_only_the_mandatory_options_are_provided_by_the_user_via_toml_file() {
+        figment::Jail::expect_with(|jail| {
+            jail.create_file(
+                "index.toml",
+                r#"
+                [metadata]
+                schema_version = "2.0.0"
+
+                [logging]
+                threshold = "info"
+            "#,
+            )?;
+
+            let info = Info {
+                config_toml: None,
+                config_toml_path: "index.toml".to_string(),
+            };
+
+            let settings = Configuration::load_settings(&info).expect("Could not load configuration from file");
+
+            assert_eq!(settings, Settings::default());
+
+            Ok(())
+        });
+    }
+
+    #[test]
+    fn configuration_should_use_the_default_values_when_only_the_mandatory_options_are_provided_by_the_user_via_toml_content() {
+        figment::Jail::expect_with(|_jail| {
+            let config_toml = r#"
+                [metadata]
+                schema_version = "2.0.0"
+
+                [logging]
+                threshold = "info"
+            "#
+            .to_string();
+
+            let info = Info {
+                config_toml: Some(config_toml),
+                config_toml_path: String::new(),
+            };
+
+            let settings = Configuration::load_settings(&info).expect("Could not load configuration from file");
+
+            assert_eq!(settings, Settings::default());
+
+            Ok(())
+        });
+    }
+
     #[tokio::test]
     async fn configuration_should_allow_to_override_the_tracker_api_token_provided_in_the_toml_file() {
         figment::Jail::expect_with(|jail| {