bug#26911: 25.2; eshell "cd .." doesn't work correctly with TRAMP

[Paul Eggert]

On 8/29/20 11:26 AM, Eli Zaretskii wrote:

> > That's what Emacs 27 does on MS-Windows, no? So it's not a regression, and the
> > problem can be fixed at the convenience of whoever's interested in hacking on
> > the MS-Windows side of the code.
>
> It's a regression wrt behavior on Posix platforms: it fails one of the
> tests in fileio-tests.el:

That's not a regression in the usual sense of the word, since Emacs master on 
MS-Windows is behaving the same way it did in Emacs 27. It's merely a bug that 
has been fixed on most platforms but not on MS-Windows.

The test you mentioned is newly-added and already special-cases for MS-Windows, 
and it's easy to special-case it just a bit more. I installed the attached 
little patch as a workaround until we can get the bug fixed in the MS-Windows 
support code.

> If that is the case, I prefer that we revert all the changes made
> recently to fix bug#26911, and leave that bug open, until a fix is
> available that works on all platforms.

Although we should continue to leave the bug open (since it's still present on 
MS-Windows), reverting would be the tail wagging the dog. We should not 
reintroduce a bug on GNU and similar platforms merely because we haven't yet 
found the time to fix the bug on MS-Windows.

It surely would be better to fix the bug on MS-Windows. A good way to start 
doing that is to refactor the code a bit to avoid the tricky #ifdefs it 
currently uses, as these #ifdefs make bugs like this painful to fix. I can draft 
a patch along those lines if you like. I realize you're dubious about 
refactoring and so wouldn't install the patch without checking with you.

If you prefer fixing it a different way of course feel free to suggest 
something. Since I don't use MS-Windows your expertise would be helpful.

0001-Mark-failing-fileio-test-on-MS-Windows.patch
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