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Alt+<printable key> sends the bare key with no ESC prefix (readline/emacs/tmux meta bindings lost)

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
72/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
typescript
Domain
frontend

Research direction

Start in lib/input-handler.ts, where isPrintableCharacter rejects Alt-modified keys and handleKeyDown passes them on to the key encoder. Check whether KeyEncoderOption.ALT_ESC_PREFIX is ever set. Done when a dispatched Alt+b produces the string "\u001bb", Alt+ArrowLeft and Alt+Backspace still encode as before, and the change works on Linux without breaking the macOS path referenced in #109.

Written by the indexing model from the issue text.

Description

Summary

Alt+<printable key> sends the bare key with no ESC prefix. Terminal applications rely on the meta prefix (readline Alt-b/Alt-f/Alt-d, emacs M-x, tmux/vim meta mappings), so all of them silently lose their Alt bindings. This is the Linux/Windows case of what #109 describes for macOS: isPrintableCharacter() correctly refuses Alt-modified keys, but they then reach the Ghostty key encoder without KeyEncoderOption.ALT_ESC_PREFIX ever being set, so the encoder emits just the character.

Seen on [email protected] (Chromium 14x on Linux). The same code path is unchanged on main (lib/input-handler.ts: isPrintableCharacter returns false for Alt, nothing sets ALT_ESC_PREFIX). (Shift+Tab from #109 is fixed on main but not in the published 0.4.0 -- see #137.)

Minimal reproduction

<div id="t"></div>
<script type="module">
  import { init, Terminal } from 'ghostty-web';
  await init();
  const term = new Terminal();
  term.open(document.getElementById('t'));
  term.onData((d) => console.log(JSON.stringify(d)));
  term.focus();
  // Press Alt+B, or dispatch it:
  term.element.dispatchEvent(new KeyboardEvent('keydown', { key: 'b', code: 'KeyB', altKey: true, bubbles: true, cancelable: true }));
</script>

Actual: "b". Expected (xterm.js, every native terminal, Ghostty itself with macos-option-as-alt/Linux defaults): "\u001bb".

Alt+ArrowLeft ("\u001b[1;3D") and Alt+Backspace ("\u001b\u007f") are fine, so the encoder path itself works; only the printable-key case loses the prefix.

Suggested fix

Either set KeyEncoderOption.ALT_ESC_PREFIX on the encoder (it is already a defined option) and let Alt+printable go through it, or handle altKey && !ctrlKey && !metaKey && event.key.length === 1 in handleKeyDown by emitting '\x1b' + event.key (on macOS, derive the letter from event.code as proposed in #109, since event.key is the composed character there).

Found while evaluating ghostty-web as a PTY renderer for https://github.com/erisera-code/clawser; the host currently works around it with attachCustomKeyEventHandler.

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TypeScript
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