#2480 Incorrect cursor position and incorrect uncommitted text highlight while typing Japanese text

[Anonymous]

Thank you for constantly improving your software.

I am using TexStudio 2.12.22 (Build 2.12.22+debian-1build1) using Qt Version 5.12.8, compiled with Qt 5.12.5R. I am on Ubuntu 20.04.1LTS, and I am typing input using Mozc.

I am writing Japanese text, and in certain situations the round brackets ( and ) are incorrectly displayed on the text editor (however, the text I am creating compiles correctly). Furthermore, the position of the cursor is also incorrect. Furthermore, the yellow highlight of uncommitted text input is also incorrect.

I think this is an issue with multibyte characters.

Before reading this detailed report in full length, I invite you to type (or copy+paste) in the following into your text editor, and then check the location of your blinking cursor at the end of each of the following four lines:

（
あ（
ああ（
あああ（

If you could reproduce my problem, then the cursor in your editor is NOT blinking at the end of the first and last line, but blinks at the end of the second and third line.

This behavior is extremely frustrating, because even after you commit your input, the cursor is unable to move past beyond the half-width empty space, blinking at the beginning of the parenthesis, and further text input will visually overwrite your bracket while typing it, and will only "jump" the text to the correct position, after you commit to it.

Here is how to reproduce the problem (assume that you have already set your computer to type in Japanese characters). For clarity, the Japanese left open round bracket visually looks like as a half-width space followed by a half-width left open round bracket, so essentially as " (".

Action: Press shift+9 (to create a Japanese left open parenthesis).
You expect the following: a Japanese left open parenthesis is shown, highlighted in yellow, waiting to be committed, and the cursor is at the right of the parenthesis waiting for further text input.
In reality, the following happens: a Japanese left open parenthesis is shown (correctly), however, only the first half of it (= the half-width empty space) is highlighted in yellow (incorrect), and the cursor is blinking at the end of the highlight (=after the end of the half-width empty space), and not at the end of the parenthesis.

Further testing showed the following inconsistent, and incorrect behavior:

1. Typing in a single Japanese left open parenthesis is incorrect, as described above.
2. Typing in a single "hiragana a", but NOT committing to it, then typing in a Japanese left open parenthesis highlights correctly the expression "あ（", and the cursor is blinking at the correct position, at the very end of the text. This behaves, as expected.
3. Typing in two "hiragana a", but NOT committing to it, then typing in a Japanese left open parenthesis highlights correctly the expression "ああ（", and the cursor is blinking at the correct position, at the very end of the text. This behaves, as expected. However...
4. Typing in three "hiragana a", but NOT committing to it, then typing in a Japanese left open parenthesis is once again incorrect, the same way as if just a single Japanese left open parenthesis would have been typed in (see the beginning of this report): The yellow background highlighting the uncommitted text only covers あああ and the first half of the Japanese left open parenthesis, and the cursor is blinking at the wrong position, NOT at the end of the text, but instead halfway at the middle of the Japanese left open parenthesis.

Thank you for looking into this issue.

[Benito van der Zander]

see here: https://github.com/texstudio-org/texstudio/issues/1099#issuecomment-632485580