Text typed in IME mode disappears

[t-hamano]

Hi.
I have encountered a problem where text entered in IME mode disappears when the following conditions are combined

• inputStyle is contenteditable
• Input after tab indentation

Screencast reproducing the issue

I tracked down the code and found that domTextBetween returns empty when the problem occurs.

codemirror5/src/input/ContentEditableInput.js

Line 307 in f006b57

let newText = cm.doc.splitLines(domTextBetween(cm, fromNode, toNode, fromLine, toLine))

My guess is that the walk() function, which recursively finds text, is not finding the correct text in the case of tab indentation. I have tried to plant console.log(node) at the beginning of the walk() function, but it seems that the parsing results are different if the indentation is space or tab.

Space indent

Tab Indent

As you can see, in the case of tab indentation, the span tags are nested, and I expect this is the reason why the text cannot be extracted correctly.
Perhaps we need to handle the case where span.cm-tab-wrap-hack is found.

Hope this report helps. Also, I use IME input mode all the time, and I will be happy to help with testing if you need..