Enum LineItem 

#[non_exhaustive]
pub enum LineItem {
    Segment {
        id: Cow<'static, str>,
        segment: Box<dyn Segment>,
    },
    Separator(Separator),
}

One slot in a line layout: a configured segment or an inline separator between segments. The builder (build_segments / build_lines) interleaves separators between adjacent segments from [layout_options].separator; the renderer walks this list directly. See docs/specs/segment-system.md §Data model.

A plugin’s per-render override (RenderedSegment::with_separator) beats the inline Separator only when an inline-separator slot exists immediately to the segment’s right. An override on the rightmost segment, or a segment whose right-neighbor separator has already been pruned, has no boundary to apply to and is silently discarded.

Per-variant #[non_exhaustive] is omitted from LineItem::Segment because consumers pattern-match { id, segment } directly and the consumer set is narrow (builder + tests + benches). Contrast LayoutDecision’s per-variant #[non_exhaustive] (ADR-0026 §C): those events are observability surfaces with an unknown consumer set, so field-additive forward-compat justifies the , .. pattern cost.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Segment

A segment paired with the user-facing config id that names it (per ADR-0026). Sourced from LineEntry::segment_id() (the TOML key).

id is a label, not an identity: the layout engine threads it through LayoutDecision events but does not verify it against the inner segment’s type. External constructors must keep the two in sync.

Cow::Borrowed vs Cow::Owned is a per-emit allocation trade-off, not a correctness invariant. Built-in ids land as Cow::Borrowed; plugin and user-config ids land as Cow::Owned. External constructors that don’t preserve this partition are correct but pay one extra allocation per built-in emit.

Fields

id: Cow<'static, str>

segment: Box<dyn Segment>

Separator(Separator)

Trait Implementations

impl Debug for LineItem

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.