bug#60929: 30.0.50; [FR] `file-name-extension' and backup suffixes

[Ruijie Yu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Ihor Radchenko <yantar92@posteo.net> writes:

> Hi,
>
> Would it be possible to make `file-name-sans-extension' strip extension
> upon removing backup suffixes (optionally)?
>
> Currently, Emacs' handling of backup extensions is a bit inconsistent:
>
> auto-mode-alist recognizes
>
>  ("\\.~?[0-9]+\\.[0-9][-.0-9]*~?\\'" nil t)
>  ("\\.\\(?:orig\\|in\\|[bB][aA][kK]\\)\\'" nil t)
>
> as backup extension and thus opens files like foo.org.bak with Org mode.
>
> [...]
>
> It would be useful if functions like `file-name-extension',
> `file-name-sans-extension', and similar could optionally strip backup
> suffixes that contain ".".
> [...]

Note that since the backup extensions can be stripped recursively in
`auto-mode-alist' (that is, "test.c.bak.Bak.BAK.baK" is opened in c-mode
because of the recursive extension stripping), if this FR is to be
accepted, we would need to ensure that the above scenario is covered.

Best,


RY