feat!: [torrust#938] add mandatory config options

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.

The mandatory options are:

```toml
[metadata]
schema_version = "2.0.0"

[logging]
threshold = "info"

[core]
private = false
listed = false
```

packages/configuration/src/lib.rs

@@ -303,6 +303,12 @@ pub enum Error {
 
  #[error("Unsupported configuration version: {version}")]
  UnsupportedVersion { version: Version },
+
+ #[error("Missing mandatory option: {path}")]
+ MissingMandatoryOption { path: String },
+
+ #[error("Missing figment metadata for mandatory option: {path}")]
+ MissingMandatoryOptionMetadata { path: String },
 }
 
 impl From<figment::Error> for Error {

packages/configuration/src/v2_0_0/mod.rs

@@ -332,6 +332,8 @@ impl Configuration {
  .merge(Env::prefixed(CONFIG_OVERRIDE_PREFIX).split(CONFIG_OVERRIDE_SEPARATOR))
  };
 
+ Self::check_mandatory_options(&figment)?;
+
  let config: Configuration = figment.extract()?;
 
  if config.metadata.schema_version != Version::new(VERSION_2_0_0) {
@@ -343,6 +345,49 @@ impl Configuration {
  Ok(config)
  }
 
+ /// 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", "core.private", "core.listed"];
+
+ for mandatory_option in mandatory_options {
+ let app = figment
+ .find_value(mandatory_option)
+ .map_err(|_err| Error::MissingMandatoryOption {
+ path: mandatory_option.to_owned(),
+ })?;
+
+ let metadata = figment
+ .get_metadata(app.tag())
+ .ok_or_else(|| Error::MissingMandatoryOptionMetadata {
+ path: mandatory_option.to_owned(),
+ })?;
+
+ match &metadata.source {
+ Some(source) => {
+ if let figment::Source::Code(_) = source {
+ return Err(Error::MissingMandatoryOption {
+ path: mandatory_option.to_owned(),
+ });
+ };
+ }
+ None => {
+ return Err(Error::MissingMandatoryOption {
+ path: mandatory_option.to_owned(),
+ })
+ }
+ }
+ }
+
+ Ok(())
+ }
+
  /// Saves the configuration to the configuration file.
  ///
  /// # Errors