editor-model

editor-model is the frontend side of the edit service: everything an editor needs that is not drawing. It has no UI toolkit, needs no async runtime and does no Bus I/O. The transport stays in the consumer; the mirror only produces requests (types::Outgoing) and consumes replies and events.

Used by:

• editor, the shared egui editor widget, which turns keys and pointer events into EditCommands;
• ced and its documents crate, including ced --headless, which drive the mirror against editd.

It builds on the edit library (Text, ot, view, wire, origins) and the syntax crate (lsh highlighting).

The source is libs/editor-model.

Modules

The editor model

EditorModel::command(&text, &cfg, command) applies an EditCommand to the current view text and returns the LocalEdit to send, or None for a pure motion. Commands: insert, newline, backspace, delete, delete word left or right, tab, outdent, duplicate line, delete line, move line up or down, toggle comment, Move { to, extend }, select all, select word (double-click), select line (triple-click) and set selection. Motions are left and right, word left and right, up and down, smart Home, End, page up and down, document start and end, and To(offset).

The contracts, from the module docs:

• Every motion is grapheme-correct through edit::view; Up and Down keep preferred_cells.
• A multi-line Tab or Outdent is one multi-item LocalEdit: one edit.apply, one undo group. coalesce is set only for single-grapheme typing and backspace/delete runs.
• Newline copies the line's leading whitespace and uses the buffer's line ending. ToggleComment uses the language's line-comment token (line_comment_for: -- for Mix, // for Rust, C, C++, Go and JavaScript, # for shell, Python, TOML and YAML; other languages get nothing).
• apply_delta maps the selection, remote carets and markers through a ViewDelta. A delta that overlaps the composition range cancels it.
• Lines are 1-based, cells 0-based.

use edit::text::Text;
use edit::view::MeasureCfg;
use editor_model::model::{EditCfg, EditCommand, EditorModel};

let cfg = EditCfg {
    measure: MeasureCfg { tab_size: 4, ambiguous_wide: false },
    insert_spaces: true,
    eol: "\n",
    line_comment: Some("--"),
};
let text = Text::from_text("hello\n").unwrap();
let mut m = EditorModel::default();
let edit = m.command(&text, &cfg, EditCommand::Insert("> ".into()));
// `edit` is Some(LocalEdit { items, coalesce, caret_after }) for the mirror.

The mirror

Mirror::bootstrap starts from an edit.open reply. The host then feeds it local_edit, server_op (undo, redo, save, reload, apply at a revision), on_event (edit.changed), on_reply, on_deadline, on_page and on_history, and after every call drains next_outgoing, take_retry_timer, take_echo_timer and take_outcomes. The deltas it produces are ViewDeltas, the one thing the editor side consumes: how the view text changed, with its kind (Local, Remote, Undo, Redo, Reload, Revert, Resync), revision and view generation.

The rules are binding and written out in the module docs of src/mirror.rs: one request in flight per buffer; how a server edit is folded (duplicate, gap, own ack, or a remote fold that rebases pending ops and reports a Conflict); how replies, busy backoff and refusals are handled; what happens at a deadline; recovery from an event gap, a reconnect or an epoch change (history first, then a paged snapshot); and the keep-mine transfer of a detached copy, staged over 1 MiB.

Highlighting and diagnostics

• Highlight: lsh languages are checkpointed every 1024 lines and seek under a per-frame SliceBudget; a line not reached yet draws plain. Mix languages (mix, scene, mix-data) are relexed whole off the UI thread, 150 ms after the last delta (the caller debounces and runs the worker); buffers over 2 MiB stay plain. A result tagged for another epoch, buffer, language or config is discarded; an older result is used only above the first line touched since.
• Diagnostics: one set per source. LINT_SOURCE is the frontend's own mix lint --json - run (schema version 2 only); any other source is an external set (ced.diagnostics). A diagnostic whose line was touched since its tagged generation is dropped; the rest map through the deltas.

Features

• mix (the crate default; the workspace dependency turns default features off, and ced and editor enable it): Mix highlighting through the Mix lexer. Without it, Mix buffers draw plain.
• fake: the fake module, for consumers' tests. ced's tests enable it.

Testing

Unit tests sit beside each module (src/model/tests.rs, src/highlight/tests.rs, src/diag/tests.rs). The mirror is tested end to end against FakeEditd:

• tests/fixture_server_side.rs runs the server side of every scripted scenario in tests/fixtures/mirror/ (format in its README), so a contradictory fixture fails there first.
• tests/mirror_convergence.rs replays every fixture through a real Mirror, checking the exact requests sent and the declared client expectations, then runs proptest properties over random interleavings of typing, agent edits, undo, reordered or dropped events and replies, lost requests, deadlines and dedup eviction. The emitted deltas are replayed onto a shadow string that must match the mirror's text.

On an authorised build worker:

cargo test --locked -p editor-model

A vertical-motion benchmark is #[ignore]d; run it in release on a build node.