Editor:
- Render monospace ascii
- Cursor movement
- Insert/delete text
- Selections
- Multiple cursors
- Multiple editors sharing one buffer
- Mouse interactions
- Cut/copy/paste
- Load/save
- Soft wrap
- Scrolling
- Undo/redo
- Status bar
Tools:
- Open file
- Search project files
- Search open buffers
- Search within buffer
- Search within project files
- Navigation stack
- Runner
- Search errors
- Bound in-buffer search results - one long line of matches builds a
list quadratic in its length (known failure, reproduced by
focus-core/tests/review_regressions.rs)
Language specific:
- Rust
- Python
- Shell
- Nix
- Markdown
- Highlighting
- Comment/uncomment
- Smart indent
- Manual indent (esp python)
- Paren matching
- Formatting
- Completion UI
Language server:
- Squigglies
- Completions
- Actions
VCS:
- Diff
- Traffic lights in editor gutter
- Revision picker
Testing:
- Deterministic simulation testing
- E2E fuzzing
- Replayable history of live sessions, for later debugging
- Test that IO functions are not reachable from focus-core build
- Max out fuzzer coverage
- Figure out how to effectively test daemonization and timeouts
Arch:
- Daemonize
Perf:
- Don't store undo for readonly buffers
- Test that fuzzer actions take at most linear time in buffer size
- Test that fuzzer actions never take longer than frame budget
- more text structure
- https://matklad.github.io/2023/03/08/an-engine-for-an-editor.html
- https://github.com/matklad/abont
- structured forms rather than adhoc ui
- eg code folding - surprisingly hard to support simply
- in general want it to be much easier to add ui. not custom per task.
- terminal editor
- ghostty helpful here?
- https://matklad.github.io/2025/08/31/vibe-coding-terminal-editor.html
- undo tree
- lsp
- magit (https://matklad.github.io/2026/03/05/jj-lsp-followup.html)
- file tree / dired
- tentative ideas for agent integration
- point agent at special comments, open magit diff, add review comments, run again
- conversation tree?