Struct DiffMode 

pub struct DiffMode;

diff-mode minor. Empty marker in v1 (D.5.a): the bit other layers consult. D.5.b/c land the do/dp chord bindings against the MinorMode(ModeId::new("diff-mode")) keymap layer (K.1.b shape).

Implementations

impl DiffMode

pub fn mode_id() -> ModeId

Trait Implementations

impl Mode for DiffMode

fn keymap(&self) -> Keymap

MO.x (2026-06-24): contribute the do/dp chords through the standard Mode::keymap() seam (the multibuffer ]e/[e pattern). The host’s K.2.4 translation pass resolves each entry’s cmd name against the CommandRegistry and pushes the layer under MinorMode(diff-mode), gated to diff-active buffers by K.1.c — retiring the host’s bespoke explicit push_layer (the emacs-keys host-push that DX.5/DX.7 left as this follow-up). The binding choice now lives wholly with the mode; the host pushes nothing diff-specific.

fn action_handlers(&self) -> Vec<ActionHandlerContribution>

CR.1 (2026-06-24): the do/dp chord handler bodies, now mode-owned (they were Editor::do_diff_get/do_diff_put + Action::DiffGet/DiffPut host-side). Bound globally (buffer-agnostic) at boot by the host’s register_mode_action_handlers walk: diff-mode is active on many buffers at once and the ActionHandlerRegistry is keyed by CommandId alone, so a per-on_activate registration would let one buffer’s deactivation evict the handler for the others — the snippet action:snippet-expand precedent. Each handler reads the active buffer + cursor from the ActionContext and the diff session from the DiffSubsystemHandle service, resolves the hunk via DiffSubsystem::diff_*_effect, and hands the host an Effect::ApplyEdit (CR.0): the mode owns the resolution, the host owns the apply. do/dp pass None as the target (auto-resolve the peer in 2-way; “target required” in 3-way); the :diffget/:diffput optional <bufnr> is a separate host call into the same diff_*_effect resolver.

fn on_activate( &self, ctx: ModeContext, ) -> Pin<Box<dyn Future<Output = Result<DiffModeGuard, ModeActivationError>> + Send + '_>>

DX.3-C7 (2026-06-24) / D-fix.5 (2026-06-26): register the buffer’s diff fold sources.

Mirrors MultibufferMode::on_activate: pull the FoldOverlayService + the data handle (DiffSubsystemHandle) + the ConfigRegistry from the service registry, resolve the diff session and the buffer’s ranges slot, and register TWO sources over them:

• HunkFoldSource — folds the hunks (open by default);
• UnchangedFoldSource (D-fix.5) — folds their complement, the unchanged gaps (closed by default; vimdiff foldmethod=diff).

D-fix.5 resolves via lookup_session_for (not the primary-only lookup) + participant_slot, so EVERY participant — including the baseline-side secondary buffer — registers sources folding its OWN side. Both panes fold in lockstep; under scroll-bind, folding only one side would desync the side-by-side view.

The returned DiffModeGuard’s Drop removes both sources when the mode deactivates. Missing service / no session / no slot just skips (empty guard) — folds inactive, never a panic.

type Guard = DiffModeGuard

Owned cleanup token returned by Self::on_activate.

fn id(&self) -> ModeId

Canonical identity. Same value every call.

fn kind(&self) -> ModeKind

Major or minor. Read at registration and on every activation call (activate_major on a minor, or vice versa, is ModeActivationError::WrongKind).

fn gutter_decorations(&self, ctx: &DecorationCtx<'_>) -> Vec<GutterDecoration>

Gutter sign decorations this mode contributes while active. Called once per pane per frame with a DecorationCtx carrying relevant render-state snapshots (diff sign map, LSP diagnostics arc). Returns per-line GutterDecoration values; the renderer partitions them by variant into the appropriate gutter column. Default: empty (no contribution).

fn target_buffer_kind(&self) -> Option<BufferKind>

For major modes, the BufferKind this mode is the default major for (H.2, 2026-05-31). ModeRegistry::register indexes this so ModeRegistry::find_major_for_kind can dispatch buffer-creation events to the right major without host-side match BufferKind { ... } blocks.

fn target_language(&self) -> Option<&str>

For major modes, the language this mode is the default major for, by canonical name (Lang::name() — "rust", "org") (OM.1). The peer of target_buffer_kind for the dispatch path BufferKind::Document takes: language detection rather than kind dispatch.

fn options(&self) -> OptionOverrideSet

Option overrides this mode contributes. Pure declarative (same return value every call); the host merges these into the buffer’s option-resolution layer stack while the mode is active, at the mode’s layer (later-activated minors win ties), and drops them on deactivation. Build with lattice_config::overrides! { lattice_config::Wrap = true, … }.

fn decorations(&self) -> Vec<DecorationProvider>

Decoration providers (gutter / inline / overlay / statusline). Stub — reserved for the WIT plugin path (M.10).

fn completion_sources(&self) -> Vec<CompletionSourceContribution>

Insert-mode completion sources this mode contributes while active on a buffer. Empty by default; minors that own a completion source (lsp-completion-mode, snippet-completion-mode, buffer-words-mode, tree-sitter-completion-mode, path-completion-mode, plugin sources) override.

fn required_capabilities(&self) -> CapabilitySet

Capabilities the mode requires. Validated at activation; missing capability ⇒ ModeActivationError::MissingCapability, never silent skip.

fn conflicts_with(&self) -> &[ModeId]

Modes this one cannot be active alongside.

fn implies(&self) -> &[ModeId]

Minor modes activating this mode also activates. Used by relative-line-numbers-mode ⇒ line-numbers-mode, and by read-only majors ⇒ read-only-mode.

fn presents_extensions(&self) -> &[&'static str]

File extensions (lowercase, no dot) this major PRESENTS rather than edits — the file is never loaded as text.

fn mirrors_option(&self) -> Option<&'static str>

Declarative mirror hint for “this mode is the on/off switch for a typed option of the same observable state”. Some(canonical_name) ⇒ a host-driven cascade keeps the mode’s active state and the option’s value in sync.

fn invocation_runner(&self) -> Option<ModeId>

Invocation-runner discovery (2026-05-26). Modes that own command-invocation dispatch for their buffer kind (terminal-mode, oil-mode, file-tree-mode, help-mode, …) return their canonical ModeId; the host registers a runner function under that id at boot, and Editor::run_invocation looks it up by walking the active modes on the active pane’s buffer (minors first, then major) before falling back to the central grammar Action gate.

fn refresh_action(&self) -> Option<&'static str>

Which of this mode’s own actions refreshes its view, or None (the default) when the mode backs nothing refreshable (RV.1, 2026-08-10).

fn fold_toggle_action(&self) -> Option<&'static str>

Which of this mode’s actions <Tab> fires, and the declaration that pulls in foldable-view-mode — the shared minor owning the chord.

fn refresh_on_open(&self) -> bool

Should re-opening this view re-run its refresh?

fn activation_policy(&self) -> ActivationPolicy

A minor mode’s default auto-activation policy (MA.1; mode-architecture.md §7.4). The host’s minor-activation resolver reads this for every registered minor when a buffer enters a major mode, and activates those whose policy admits the entered major. The default is ActivationPolicy::Manual — auto-activate nowhere until the mode or the user opts in. Ignored for major modes (a buffer’s major is chosen by the major resolver, not this allowlist).

fn editable_tail(&self) -> Option<EditableTail>

The mode’s editable tail on an otherwise read-only buffer, or None (the default) for a fully read-only / fully writable buffer (AU‑3).