Gvim 8.2 displays "Can't open file for writing" with a windows files that have a Unicode colon in the file name. Notepad, Wordpad, LibreOffice all work.
You mentioned in the comments, that the "unicode colon" is
According to codetable.net this is a
- "：" (Fullwidth Colon)
- ":" (normal colon)
I tested files with this character in its name on
- Vim on Linux -> OK
- Vim in Git Bash on Windows (MSYS2) -> OK
- Vim on Windows -> NOT OK
I only have a rather old 8.1.2188 available on Windows 10. On loading the file the Fullwidth Colon was replaced by a normal colon. So in fact Vim is not editing the file given as parameter (or selected via file dialog or opened via drag and drop).
So this is not the problem you see, but there is something wrong.
The problem in this case is, that the encoding of Vim internally is "latin1", a single-byte character set. So the file name is converted to latin1 and this results in replacing the Fullwidth Colon with a normal colon.
I changed the internal character set by adding
as the first line of my vimrc.
Just try this. After you restarted Vim you can execute
to validate that the encoding is really "utf-8". If not, something is resetting
it -- maybe you have a superfluous
With encoding set to utf-8 I can load and save the file containing the Fullwidth Colon in the name.