This document contains a high-level overview of Helix internals.

NOTE: Use cargo doc --open for API documentation as well as dependency documentation.

Core

The core contains basic building blocks used to construct the editor. It is heavily based on CodeMirror 6. The primitives are functional: most operations won't modify data in place but instead return a new copy.

The main data structure used for representing buffers is a Rope. We re-export the excellent ropey library. Ropes are cheap to clone, and allow us to easily make snapshots of a text state.

Multiple selections are a core editing primitive. Document selections are represented by a Selection. Each Range in the selection consists of a moving head and an immovable anchor. A single cursor in the editor is simply a selection with a single range, with the head and the anchor in the same position.

Ropes are modified by constructing an OT-like Transaction. It's represents a single coherent change to the document and can be applied to the rope. A transaction can be inverted to produce an undo. Selections and marks can be mapped over a transaction to translate to a position in the new text state after applying the transaction.

NOTE: Transaction::change/Transaction::change_by_selection is the main interface used to generate text edits.

Syntax is the interface used to interact with tree-sitter ASTs for syntax highling and other features.

View

The view layer was supposed to be a frontend-agnostic imperative library that would build on top of core to provide the common editor logic. Currently it's tied to the terminal UI.

A Document ties together the Rope, Selection(s), Syntax, document History, language server (etc.) into a comprehensive representation of an open file.

A View represents an open split in the UI. It holds the currently open document ID and other related state.

NOTE: Multiple views are able to display the same document, so the document contains selections for each view. To retrieve, document.selection() takes a ViewId.

The Editor holds the global state: all the open documents, a tree representation of all the view splits, and a registry of language servers. To open or close files, interact with the editor.

LSP

A language server protocol client.

Term

The terminal frontend.

The main function sets up a new Application that runs the event loop.

commands.rs is probably the most interesting file. It contains all commands (actions tied to keybindings).

keymap.rs links commands to key combinations.

TUI / Term

TODO: document Component and rendering related stuff