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

[Ken Brown <kbrown@cornell.edu>]

On 4/22/2024 12:15 PM, Ken Brown wrote:
> On 4/17/2024 8:21 AM, Eli Zaretskii wrote:
>>> Date: Wed, 17 Apr 2024 08:58:42 +0900
>>> From: Katsumi Yamaoka <yamaoka@jpl.org>
>>> Cc: 70415@debbugs.gnu.org
>>>
>>> On Tue, 16 Apr 2024 16:32:17 +0300, Eli Zaretskii wrote:
>>>>> .#FILE -> username@hostname.1234:-11644473599
>>>>> For that case `(unlock-file "FILE")' issues this warning:
>>>>> Warning (unlock-file): Unlocking file: Invalid argument, FILE, ignored
>>>
>>>> The part after the colon is the system boot time, and is used on all
>>>> Posix hosts.
>>>
>>> Oh, I had never seen it until recently.  Thanks.
>>
>> The question is: why it started appearing only recently?  The code in
>> filelock.c hasn't changed since last December, if not earlier, so if
>> this started happening recently, it could only be because Gnulib's
>> get_boot_time or its Cygwin implementation changed, such that it was
>> previously returning zero whereas now it returns non-zero (which
>> triggers the addition of the ":BOOT_TIME" part to the file name).
>>
>>>>> | commit 393f58c85aeb78f814866ccaad9ae7efd3fa6766
>>>>> | Author: Adam Porter <adam@alphapapa.net>
>>>>> | Date:   Fri Mar 8 23:43:14 2024 -0600
>>>
>>>> This is extremely unlikely to have caused the problem.  It is more
>>>> likely that some change in Cygwin and/or in the Gnulib's boot-time
>>>> module causes this now.
>>>
>>> Indeed.  But the fact is that Emacs built with that revno adds
>>> a colon and a negative number to a link name and the one built
>>> with just before it does not.  No problem on 29.3.50 and earlier,
>>> either (i.e., not add a colon and numbers).
>>
>> Then please step with a debugger through the relevant code in
>> filelock.c, before and after that change, and see why they are
>> different.  I cannot explain that, even after doing "git log -L" on
>> all of filelock.c: the most recent change of the related code was in
>> Aug 2023, AFAICT, which is a very far cry from Mar 2024.
>>
>> And even if we understand why you now get the ":BOOT_TIME" part,
>> there's still the question why it cannot be unlinked, if Cygwin
>> supports file names with a colon.  Maybe it's because Emacs creates a
>> symlink, and symlinks with such names are not supported by Cygwin?
> 
> I'm still traveling for another week and won't have time to try to 
> reproduce and debug this until I return.  But I did do one quick test in 
> a Cygwin shell.  I created a symlink
> 
>    .#FILE -> username@hostname.1234:-11644473599
> 
> and deleted it with rm.  So symlinks like this are indeed supported by 
> Cygwin.
> 
> To be continued...

I finally had a chance to look at this, and I can't reproduce the 
problem.  The autosave file does not have the ":BOOT_TIME" part, and it 
gets deleted properly when the file is saved.  I'm running the latest 
stable release of Cygwin (3.5.3) on Windows 11 (version 23H2, build 
22631.3447).

Ken