bug#64164: 29.0.92; buffer-file-coding-system changes unexpectedly after saving

[Michael Albinus]

miranda@pulusound.fi writes:

Hi Miranda,

> i am trying to edit remote files on another macOS system, using
> Tramp's ssh: method. i am running `emacs -Q`.
>
> when i open any file on this remote system, the initial value of
> `buffer-file-coding-system` is what i would expect,
> i.e. undecided-unix or utf-8-unix, depending on whether the file
> contains non-ASCII characters.
>
> however, after saving the file, `buffer-file-coding-system` suddenly
> changes to utf-8-hfs-mac. any subsequent save then changes all the
> line endings to CR, which i have not actively used since 2001 or
> so... :-)

Well, if Tramp detects a remote macOS system, it converts the coding
system to `utf-8-hfs-mac', see function
`tramp-open-connection-setup-interactive-shell'. This heuristic works
for many years w/o complaints from users.

We could suppress this. However, Tramp needs an indication when to
suppress. Do you have somthing like this?

> Emacs 28.2 works as expected.

This surprises me. I don't remember we have changed something here in
Tramp (but I might be wrong).

> best,
> miranda

Best regards, Michael.