The previous shape guessed the character from `event.key` on keydown, re-emitted
it, and then tried to suppress a late canonical copy with a 250 ms
character-keyed dedupe. Review found three defects in that, all reproducible:
the dedupe matched on the character alone with nothing scoping a candidate to
the keydown that created it, so the same character typed twice inside the window
had its second, real byte swallowed; anything whose committed text differed from
`event.key` (Enter, IME punctuation) was delivered twice, because the dedupe
could never match it; and the trigger ignored `key === 'Unidentified'`, which is
what a soft keyboard reports, so it may never have fired where it was needed.
The input event already carries the committed text in `ev.data` — exactly what
xterm itself would have forwarded — so nothing has to be guessed. The controller
now only decides WHETHER to forward, by asking whether xterm produced canonical
data since the keydown that began the keystroke. No character-keyed matching
survives, so the first two defects are structurally impossible rather than
defended against, and nothing reads `key`/`keyCode`, so the third cannot recur.
Three details are load-bearing and each has a test that fails without it:
- The "did xterm speak?" snapshot is taken at KEYDOWN, not at the input event.
`_keyPress` emits and sets `_keyPressHandled` before `input` fires, so a
snapshot read at input time already contains that emission, reads it as
silence, and delivers the character twice.
- Our `input` listener is registered with `capture: true`. The target is visited
twice in the event path, so a capture listener calling `stopPropagation()`
stops later BUBBLE listeners on that same target; xterm's `cancel()` runs
exactly in the branch where it handled the input, so on bubble we would never
observe handled events, and whether we observed them at all would hang off
`options.cancelEvents`. Measured in jsdom and headless chromium; the table is
in the module header.
- Enter is deliberately no longer special-cased. That mapping is what made the
committed text differ from the re-emitted value in the first place.
The scope is also narrower than the old name suggests, and the browser test now
proves it rather than assuming it. For a keydown that reports keyCode 229 xterm
ALREADY self-rescues, via `CompositionHelper._handleAnyTextareaChanges()`
diffing the helper textarea on a 0 ms timer. A test asserting "we recovered it"
there passes while xterm does all the work, so the browser tests assert WHO
delivered the byte: zero canonical emissions for the genuinely orphaned case,
exactly one delivery for the case xterm rescues itself.
Also addresses review notes: the module gains an `@fileoverview` with
`@dependency`/`@loadorder` and an entry in the load-order list and module
inventory, and the wiring test moves out of the Ctrl+C smart-copy file into its
own. The keydown hook deliberately still runs for every key event rather than
moving behind the 229 gate: gating it would reinstate exactly the blindness
described above, and it is now a single counter assignment.
Android/GBoard-style keyboards fire keydown with keyCode 229 and, on some
paths, never mutate xterm's helper textarea. xterm has nothing to diff, so
it emits no data and the typed character is silently dropped: it never
reaches the PTY and never appears on screen.
terminal-keycode229-recovery.js is a standalone controller that re-emits
exactly those keys, and only once. xterm stays authoritative throughout:
- Only an explicit keyCode 229 keydown carrying a single printable key (or
Enter) is eligible; Process/Unidentified/Dead, modifiers, AltGraph and a
live composition are all left alone.
- The re-emit is scheduled from a microtask and then a zero-delay timer, so
xterm's own textarea diff always gets the first opportunity; canonical
data for the same key cancels the pending fallback.
- compositionstart and blur drop every pending candidate, so a real IME
composition lifecycle is never second-guessed.
- After a recovery, one late canonical value attributed to that key token
(via beforeinput/input on the helper textarea) is suppressed so the
character cannot be delivered twice; the record expires after 250ms and
an unattributed byte is never suppressed.
terminal-ui.js wires it at the two existing choke points — the custom key
handler and the onData registration, the latter now a named handler so the
recovery path can re-enter it — with both hooks wrapped so a failure in the
fallback can never break canonical input.
Unit coverage drives the module directly in a vm; the wiring itself is
covered end-to-end in the (browser-only) terminal-copy-shortcut suite.
Aamer Akhter