mcedit: Wrong cursor position with 8-bit locale after nonprintable Unicode character

[egmontkob]

Is there an existing issue for this?

• I have searched the existing issues

Midnight Commander version and build configuration

4.8.33, current git

Operating system

Linux

Is this issue reproducible using the latest version of Midnight Commander?

• I confirm the issue is still reproducible with the latest version of Midnight Commander

How to reproduce

Create a file that contains some non-printable Unicode character (e.g. U+FEFF or U+10FFFF) encoded in UTF-8, perhaps followed by a few ASCII letters.

Start mcedit with an 8-bit locale (and the same 8-bit charset in the terminal). Open the file with UTF-8 as the file's encoding (this is the default, verify with Alt-E).

The said Unicode character is displayed as a single dot. Press the right arrow to jump over this character. The cursor moves by 3 or 4 columns, corresponding to the number of bytes in the UTF-8 sequence.

Insert new letters, or just observe the shown character code in the header: the cursor is consistently shown at the wrong offset. While on the display (the terminal's contents) the said character occupies 1 column, the cursor jumps as if that character occupied 3-4 columns.

Expected behavior

.

Actual behavior

.

Additional context

No response

[egmontkob]

Related: #3257. Possible duplicate (hard to tell): #3215.

[egmontkob]

This was an utterly random uneducated guess, my very first guess without having debugged anything about the problem, but it seems I got lucky, removing the isprint condition here seems to solve the problem:

https://github.com/MidnightCommander/mc/blob/4.8.33/src/editor/edit.c#L2842