bug#70415: 30.0.50; [Cygwin] `lock-file' creates a symlink with funny name

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 16 Apr 2024 18:57:21 -0400
> Cc: 70415@debbugs.gnu.org
> From: Ken Brown <kbrown@cornell.edu>
> 
> On 4/16/2024 9:32 AM, Eli Zaretskii wrote:
> >> Date: Tue, 16 Apr 2024 21:33:07 +0900
> >> From: Katsumi Yamaoka <yamaoka@jpl.org>
> >>
> >> As you know, Emacs creates a lock file when start editing a FILE
> >> by default, it is a symbolic link that is linked to a name
> >> looking like this:
> >>
> >> .#FILE -> username@hostname.1234
> >>
> >> Where 1234 is Emacs' pid.  It will be removed after saving
> >> the FILE.  Even if the lock file is left, Emacs will remove it
> >> when opening the FILE for the next time.  However, recently lock
> >> files no longer got deleted on at least the latest Cygwin on
> >> Windows 11.  It is (probably) because Emacs came to create lock
> >> files with a funny name like this:
> >>
> >> .#FILE -> username@hostname.1234:-11644473599
> >>
> >> For that case `(unlock-file "FILE")' issues this warning:
> >>
> >> Warning (unlock-file): Unlocking file: Invalid argument, FILE, ignored
> > 
> > Does Cygwin support file names with a colon, such as the above?
> 
> I'm traveling at the moment, and it will be a while until I have a 
> chance to look at this report closely or try to reproduce it.  But I can 
> answer your question: Cygwin does support file names with a colon.  This 
> is documented at
> 
>    https://cygwin.com/cygwin-ug-net/using-specialnames.html

That's what I thought.  But in that case, someone will have to step
through the code in filelock.c and tell why removing these lock files
fails in the Cygwin build of Emacs.