Deletion on Android IME re-propigates previous composition

[ink404]

After completing a composition on Android devices deleting re-triggers a composition and propagates the input with the old composition text. (see video below).

I was able to achieve the desired behavior by clearing the _textarea (by calling _textarea.value = '';) when compositions are finalized in CompositionHelper here: https://github.com/xtermjs/xterm.js/blob/master/src/browser/input/CompositionHelper.ts#L171.

Unfortunately this breaks the following test cases for Korean.

 1) CompositionHelper
       Input
         Should insert simple characters:

      Uncaught AssertionError: expected 'ㅇㅇㅇ' to equal 'ㅇㅇ'
      + expected - actual

      -ㅇㅇㅇ
      +ㅇㅇ
      
      at Timeout._onTimeout (src/browser/input/CompositionHelper.test.ts:65:22)
      at listOnTimeout (node:internal/timers:557:17)
      at processTimers (node:internal/timers:500:7)

  2) CompositionHelper
       Input
         Should insert complex characters:

      Uncaught AssertionError: expected '앙앙앙' to equal '앙앙'
      + expected - actual

      -앙앙앙
      +앙앙
      
      at Timeout._onTimeout (src/browser/input/CompositionHelper.test.ts:101:30)
      at listOnTimeout (node:internal/timers:557:17)
      at processTimers (node:internal/timers:500:7)

  3) CompositionHelper
       Input
         Should insert complex characters that change with following character:

      Uncaught AssertionError: expected '아' to equal '아아'
      + expected - actual

      -아
      +아아
      
      at Timeout._onTimeout (src/browser/input/CompositionHelper.test.ts:133:24)
      at listOnTimeout (node:internal/timers:557:17)
      at processTimers (node:internal/timers:500:7)

Details

• Browser and browser version: Chrome, 106.x
• OS version: Android 13, GBoard
• xterm.js version: 5.x

Steps to reproduce

1. type 'a'
2. tap space (finishes composition)
3. tap delete
4. Observe there are two a's now

Video:

xterm-repro.mp4

[ink404]

@Tyriar If you have any suggestions for what changes to make to solve this I'm happy to make a PR, also please let me know if there's any additional information I can provide that would make this easier to debug.

[RahjIII]

I'll add that this has been a serious ongoing issue, as standard English text entry through Android IME keyboard is almost unusable in current xtermjs. Any backspace seems to break the user's intended input.

Related PRs #3600 , #4007

[Tyriar]

/duplicate #3600