Trait OptionalSection 

pub trait OptionalSection:
    DeserializeOwned
    + Send
    + Sync
    + 'static {
    // Required method
    fn section_name() -> &'static str;

    // Provided methods
    fn requires() -> &'static [&'static str] { ... }
    fn on_error() -> OnError { ... }
    fn metadata() -> FeatureMetadata { ... }
    fn validate_enabled(&self) -> Result<(), ConfigError> { ... }
    fn load_optional(
        loader: &DefaultLoader,
    ) -> Result<FeatureState<Self>, ConfigError>
       where Self: Sized { ... }
}

Marks a typed struct as an opt-in TOML feature section.

Unlike ConfigSection, which returns T::default() for absent keys, OptionalSection treats absence as “feature disabled” and returns FeatureState::Disabled — no defaults, no error.

Required Methods

fn section_name() -> &'static str

The top-level TOML key for this section (e.g. "message_broker").

Provided Methods

fn requires() -> &'static [&'static str]

Other section keys this feature requires to be enabled before it can run.

Checked by crate::FeatureRegistryOps::validate_dependencies after all features are loaded. Default: no dependencies (&[]).

fn on_error() -> OnError

What the feature registry should do when validate_enabled returns an error.

• OnError::Fail (default) — propagate the error; startup halts.
• OnError::Disable — treat the feature as disabled and continue startup.

fn metadata() -> FeatureMetadata

Static documentation and ownership annotations for this feature.

fn validate_enabled(&self) -> Result<(), ConfigError>

Validate cross-field constraints after the section has been deserialised.

Only called when the section key is present in TOML. Default: always Ok(()).

fn load_optional( loader: &DefaultLoader, ) -> Result<FeatureState<Self>, ConfigError>

where Self: Sized,

Load this section as an optional feature from loader.

Returns FeatureState::Enabled(Self) when the key is present and valid, FeatureState::Disabled when absent, and Err for I/O, parse, or validation failures.

Note: on_error and requires are only applied when loading through crate::FeatureRegistryOps::load. Use that for full startup coordination with graceful degradation and dependency validation.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors