Interface KernelMode

crates/kernel/src/mode.rs:188–232

Controls metadata behavior for all zero kernel types.

/// Controls metadata behavior for all zero kernel types.
pub trait KernelMode: 'static + Clone + Debug + Send + Sync {
  /// `true` iff this mode carries metadata. Enables compile-time
  /// pruning: code paths gated by `if M::HAS_META { … }` are
  /// monomorphized into the dead-branch-eliminated form for the Anon
  /// implementation. Use this to guard metadata lookups so they don't
  /// execute in Anon mode.
  const HAS_META: bool;

  /// A metadata field: stores `T` in Meta mode, erased to `()` in Anon mode.
  type MField<T: MetaHash + MetaDisplay + PartialEq + Clone + Debug + Hash + Send + Sync>:
    MetaHash + MetaDisplay + PartialEq + Clone + Debug + Hash + Send + Sync;

  /// Wrap a value into a metadata field. In Anon mode, the value is discarded.
  fn meta_field<
    T: MetaHash + MetaDisplay + PartialEq + Clone + Debug + Hash + Send + Sync,
  >(
    val: T,
  ) -> Self::MField<T>;

  /// Build a metadata field from a closure. Meta runs the closure to
  /// produce the wrapped value; Anon discards the closure unevaluated
  /// and returns `()`. The fallible counterpart is `meta_field_try`.
  ///
  /// Use this at metadata-extraction sites in mode-generic code: the
  /// closure body — including arena walks, name resolution, and any
  /// other work that only matters in Meta mode — is skipped entirely
  /// when `M = Anon`, with no `Name::anon`-style placeholder
  /// construction at the call site.
  fn meta_field_with<T, F>(f: F) -> Self::MField<T>
  where
    T: MetaHash + MetaDisplay + PartialEq + Clone + Debug + Hash + Send + Sync,
    F: FnOnce() -> T;

  /// Fallible variant of `meta_field_with`. Meta runs the closure (and
  /// may return its `Err`); Anon discards the closure and returns
  /// `Ok(())`. Use for sites where missing metadata is a Meta-mode
  /// error but a no-op in Anon mode.
  fn meta_field_try<T, F, E>(f: F) -> Result<Self::MField<T>, E>
  where
    T: MetaHash + MetaDisplay + PartialEq + Clone + Debug + Hash + Send + Sync,
    F: FnOnce() -> Result<T, E>;

  /// Extract a name from a metadata field when running in Meta mode.
  fn meta_name(field: &Self::MField<Name>) -> Option<Name>;
}

/// Const-generic kernel mode. `META` controls metadata fields.
#[derive(Clone, Debug)]