Boolean Toggle - Zed Extension

A Zed editor extension that toggles boolean-like values in any language

Supported toggles

A side	B side	Variants (all automatically detected & preserved)
true	false	true / True / TRUE
yes	no	yes / Yes / YES
on	off	on / On / ON
1	0	(numeric — no case to preserve)

Case preservation

The extension detects the case style of the token under your cursor and applies the same style to the replacement:

true   →  false       (lowercase)
True   →  False       (Title case)
TRUE   →  FALSE       (UPPER CASE)
tRuE   →  false       (Mixed → falls back to lowercase)

The same logic applies to YES/NO, ON/OFF, etc.

---

Demo

// TypeScript / JavaScript
const debug = true;       // → false
if (enabled === FALSE) …  // → TRUE

// Python / YAML config
verbose: yes              // → no
mode: ON                  // → OFF

// Any config / markdown
enabled = 1               // → 0
active: Yes               // → No

---

Language support

The extension is active in 40+ languages out of the box:

To add more, append Zed's language name to the languages = [...] array in extension.toml. The canonical names are listed in Zed's default settings under "languages".

Data flow

Zed editor
  │  1. Opens any supported file → spawns boolean-toggle-lsp via stdin/stdout
  │  2. User presses Code Actions (`ctrl-.`)
  │  3. Zed sends textDocument/codeAction with cursor line + column
  │
  LSP server
  │  4. Finds which keyword the cursor is on (case-insensitive scan)
  │  5. Detects case style: Lower / Title / Upper / Mixed
  │  6. Builds replacement with matching case style
  │  7. Returns CodeAction { WorkspaceEdit { newText: "<replacement>" } }
  │
  Zed editor
     8. User selects the action → edit applied, undoable with Ctrl+Z

Token detection (find_token_ci)

Line:    "const DEBUG = TRUE && isOn"
Cols:     0     6       14    19    25
                             ^^^^  (TRUE → cols 14–17)
                                   ^^^   (ON  ← rejected: part of "isOn")

For each keyword in TOGGLE_PAIRS the function:

1. Slides a case-insensitive window of keyword.len() bytes across the line.
2. Verifies word boundaries: the byte before and after must not match [A-Za-z0-9_$] — this rejects trueValue, isFalse, $true, 10, etc.
3. Checks cursor_col ∈ [token_start, token_end] (inclusive on both ends — a cursor right after the last character still counts).

All keywords are ASCII, so byte offsets equal UTF-16 code-unit offsets (what LSP uses for column positions).

Case detection

detect_case_style("TRUE")  → Upper   (all alpha chars uppercase)
detect_case_style("True")  → Title   (first upper, rest lower)
detect_case_style("true")  → Lower   (all lowercase)
detect_case_style("tRuE")  → Mixed   (fallback → lowercase replacement)
detect_case_style("1")     → Lower   (no alpha chars → treat as lower)

---

Requirements

Tool	Notes
Rust + Cargo	stable ≥ 1.78
wasm32-wasip1 target	make dev installs it automatically
Zed	0.140+ recommended

---

Quick start (development)

# 1. Clone
git clone https://github.com/unlight/zed-boolean-toggle
cd zed-boolean-toggle

# 2. Build + install
make dev

make dev does three things:

1. builds the native lsp binary
2. copies it to ~/.cargo/bin (on $PATH)
3. builds the WASM

Load the extension in Zed

Open the Extensions panel (⌘⇧X / Ctrl⇧X) → "Install Dev Extension" → select this directory.

How the UX works

1. Place the cursor on any supported token (true, YES, on, 1, …)
2. Press Ctrl + Alt + X — the code-actions panel opens
3. The panel shows exactly one action, e.g. Toggle: TRUE → FALSE
4. Press Enter (or click) to apply

When the cursor is not on a toggle token, editor::ToggleCodeActions falls through to other code actions from TypeScript, ESLint, etc. — no interference.

Tip: the action is marked "isPreferred": true. If a future Zed version adds an "apply preferred action" command, you'll be able to bind that to get a truly single-keystroke toggle.

Running tests

make test

The suite covers:

Category	Examples
All four pair types	true/false, yes/no, on/off, 1/0
Three case styles	lower, Title, UPPER
Mixed case fallback	tRuE → false
Cursor positions	start, middle, end, one-past-end of token
Word boundaries	trueValue, isFalse, $true, 10, online, notable, yesterday
Multiple tokens per line	Cursor selects the right one
WorkspaceEdit ranges	Exact character positions verified
Action metadata	isPreferred, kind, title format
Server dispatch	initialize, didOpen, didChange, didClose
Transport	Content-Length framing round-trip

Building manually

# Native LSP binary
cargo build --release
# → target/release/boolean-toggle-lsp

# WASM extension
rustup target add wasm32-wasip1
cargo build --target wasm32-wasip1 --release
# → target/wasm32-wasip1/release/boolean_toggle.wasm

Production deployment

For the Zed extension marketplace, bundle pre-built binaries instead of relying on PATH:

// extension/lib.rs
fn language_server_command(
    &mut self,
    _id: &LanguageServerId,
    _worktree: &zed::Worktree,
) -> Result<zed::Command> {
    let (os, arch) = zed::current_platform();
    let binary = self.download_if_needed(os, arch)?; // cache in extension dir
    Ok(zed::Command { command: binary, args: vec![], env: vec![] })
}

Upload platform binaries (linux-x86_64, linux-aarch64, macos-x86_64, macos-aarch64, windows-x86_64) to a GitHub Release and download them lazily on first use via Zed's zed::download_file API. See the Zed extension docs for the full API.

Adding new toggle pairs

Edit TOGGLE_PAIRS in src/main.rs:

const TOGGLE_PAIRS: &[(&str, &str)] = &[
    ("true",    "false"),
    ("yes",     "no"),
    ("on",      "off"),
    ("1",       "0"),
    // Add yours:
    ("enabled", "disabled"),   // ← new
    ("allow",   "deny"),       // ← new
];

Rules for new pairs:

• Always lowercase canonical form (case detection/application is automatic)
• Word-boundary checking is automatic — no extra configuration needed
• Rebuild with make build and cargo install --path .

Contributing

1. Fork → branch → make test must pass green
2. Every new toggle pair or behaviour needs a matching test in main.rs
3. No new runtime dependencies without discussion — serde_json is the only one

License

MIT License (c) 2026