scrive

A from-scratch code-editor widget for iced — a headless editing engine plus an iced::advanced::Widget that renders it.

Two crates, with the dependency pointing one way:

• scrive-core — the headless engine: a rope-backed buffer, atomic multi-range transactions with mechanically-derived undo/redo, selections and multi-cursor, tracked-range decorations (diagnostics, find matches, snippet stops), an incremental syntax-highlight cache, folding, and the language-intelligence controllers. Imports no GUI crate.
• scrive-iced — an iced::advanced::Widget wrapping the core: gutter and line numbers, N-caret selections, syntax highlighting, bracket-pair colors and matching, indent guides, diagnostic squiggles, code folding, and the completion / hover / signature-help popups. Depends on scrive-core; the dependency never points back.

Features

• Rope-backed buffer with an O(1) snapshot for background work; the document-size envelope is bounded only by the u32 offset space, not a load cap.
• Atomic transactions with undo/redo — every edit is one transaction with a mechanically-derived inverse, and undo/redo flow through the same view-rebase path as forward edits.
• Multi-cursor editing, column (box) selection, and word-wise motion.
• Syntax highlighting via an incremental, viewport-windowed syntect cache; the app supplies the grammar and theme (the core ships neither).
• Bracket-pair colorization, matching, and indent guides.
• Code folding — foldable ranges, gutter chevrons, nested and inline (sub-line) collapse, and fold-aware movement.
• Find — literal search with a match set repaired per edit, so results never go stale.
• Language intelligence — completion, snippets, signature help, and hover, exposed as trait seams the integrating application implements.
• Diagnostics — squiggles, a diagnostic hover, and scrollbar overview marks.

Every derived position — a caret, a find match, a diagnostic, a snippet stop — is moved through a windowed or O(log n) update per keystroke, so no editing operation scales with the size of the document.

Design

The load-bearing idea is one fact, one owner: every derived position moves through a single mapping function on every edit, and every change is one atomic transaction with a mechanically-derived inverse — so the class of bug where two copies of one fact drift apart cannot occur, on the forward path or on undo.

The editor is a direct iced::advanced::Widget rather than a canvas::Program, because only the low-level widget API participates in iced's focus/operation protocol. It is a controlled widget: it borrows the Document immutably for drawing and emits semantic actions (Type, Move, FindNext, …); the application owns the Document and applies the actions, so the widget never mutates state behind the app's back.

Example

cargo run -p scrive-iced --example scratch

opens a real editor over a sample Rust document — type, select, find (Ctrl+F), fold, and undo/redo. The host application must load scrive_iced::CODICON_FONT at startup (iced::application(..).font(scrive_iced::CODICON_FONT)) so the fold-gutter chevrons and find-bar icons render.

License

MIT.