Struct DiffDescriptor 

pub struct DiffDescriptor {
    pub sources: Vec<Arc<dyn DiffParticipantSource>>,
    pub watch: Vec<BufferId>,
    pub participants: Vec<BufferId>,
}

The “what to diff against what” pair for a session.

sources is an arity-agnostic vector of N participant sources, one per slot in Hunk::ranges. The engine (crate::compute_diff) dispatches by sources.len() — N=2 is two-way (slot 0 = baseline / from, slot 1 = current / to), N=3 is three-way merge (slot 0 = base, slot 1 = local, slot 2 = remote), N≥4 returns DiffEngineError::Unsupported in v1.

watch is the explicit dependency declaration: every [BufferId] whose edits should wake this session. The descriptor’s author (a future :diffsplit / :Gdiff / AI-host call site) knows which sources are buffer-backed and contributes those BufferIds into watch. Static or git-blob sources contribute nothing.

Clone because the runtime sometimes wants a stable snapshot of the descriptor to feed a debounced recompute — the inner Vec<Arc<dyn ...>> and Vec<BufferId> clones are cheap (one Arc bump per source + a small heap allocation).

D.8.c shape (2026-05-31). Replaces the prior baseline + current + Option<remote> named-field triple with a single sources: Vec<...>; see [docs/dev/architecture/n-way-diff-membership.md] (docs/dev/architecture/n-way-diff-membership.md) for the rationale.

Fields

sources: Vec<Arc<dyn DiffParticipantSource>>

N participant sources in slot order. sources[i] produces the rope at Hunk::ranges[i] after a recompute. v1 supports N ∈ {1, 2, 3}; the engine returns DiffEngineError::Unsupported for N≥4.

watch: Vec<BufferId>

participants: Vec<BufferId>

D.5.a (2026-05-30): user-visible diff sides that should receive diff-mode activation while this session is registered. Distinct from Self::watch:

• watch declares edit-event subscriptions.
• participants declares which buffers are user-visible diff sides that should get the mode toggle.

For buffer-backed sources they coincide; they diverge when a baseline source contributes no live buffer (file-on-disk inline → [primary]; D.7 git baseline → [primary]). Two-pane is [baseline, primary]; D.6 three-way is [base, local, remote] (length 3).

Implementations

impl DiffDescriptor

pub fn arity(&self) -> usize

D.8.c (2026-05-31): the session’s arity — the source of truth for how many participants this session has. Equivalent to sources.len().

Trait Implementations

impl Clone for DiffDescriptor

fn clone(&self) -> DiffDescriptor

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for DiffDescriptor

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

Formats the value using the given formatter.