Weird behaviors of IME composition on iOS

AndyL · February 1, 2022, 12:40pm

Another similar issue with a little bit different repro scenario on iOS:

Just use iOS default Chinese IME(pinyin or 简体拼音) and with default vault(no 3rd party plug-in nor theme enabled).
Type “- “ for a bulleted list.
Press any key.

The input process is really weird:

Licat · February 1, 2022, 5:11pm

iOS bug tracked upstream:

github.com/codemirror/view

Improve iOS IME handling

codemirror:main ← lishid:main

opened 05:10PM - 01 Feb 22 UTC

lishid

+2 -2

FIX: Avoids text duplication in some cases caused by weird behaviors of IME comp…osition on iOS. This might not be the best code to fix this issue, please let me know if there's a better way to achieve this. This patch fixes a specific case of iOS IME composition - it doesn't seem to happen everywhere but I have one case that triggers this (notice the space in the outer span). ```html <span class="outer"><span class="inner">-</span> </span> ``` When the cursor is placed at the end, typing causes exponential character duplication. I've logged the events and it seems that the following happens: - `compositionstart` - [MutationObserver event](https://github.com/codemirror/view/blob/b286dee2d43fd1a018c77df6a1bc8bad5bd79b9b/src/domobserver.ts#L69), during which - `view.composing` is false but `view.inputState.compositionFirstChange` is true. - `m.oldValue` is `" "` and `m.target.nodeValue` is `" g"` (assuming `g` is typed). - In this case, if `flush` is called, then iOS will immediately trigger another mutation and insert the entire composition string again (in this case, "g"). - Each new character typed repeats this process, each time inserting a full copy of the composed string, causing exponential insertion. This patch causes `flushSoon` to be used when that happens, which causes iOS to properly keep detecting the correct composed string in the DOM and avoids inserting a new copy. https://user-images.githubusercontent.com/609710/152015884-1af091c9-9327-403b-b171-ad1c9b65762e.mov

AndyL · February 4, 2022, 6:03pm

Thanks and now it’s solved!