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

[Eli Zaretskii]

> Cc: 26911@debbugs.gnu.org, mattiase@acm.org, michael.albinus@gmx.de,
>  yegortimoshenko@gmail.com
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 31 Aug 2020 11:15:35 -0700
> 
> On 8/31/20 7:58 AM, Eli Zaretskii wrote:
> 
> > expand-file-name deals only with the syntax of file names.
> 
> Yes, but it does so under constraints imposed by semantics. This is why 
> expand-file-name can't simply remove *all* slashes from file names (which 
> would 
> be just a "syntax" thing, no? :-).

No, because a valid syntax of an absolute file name is to start with a
slash.

> > It is therefore perfectly valid for it to remove the trailing "/."
> > without appending a slash.
> 
> Not at all.

We disagree.  So any further argument is fruitless, because I will not
change my mind on this.  I'm pretty sure I'm right because this
function never did anything different from what I describe, until very
recently.

> In many cases that would change the meaning of the file name, and 
> expand-file-name is not supposed to do that.

Once again, the meaning of a file name is out of scope of
expand-file-name's job.

> Feel free to alter the code to fix these bugs in a different way. However, I 
> expect any such fix will be simpler if starts with the current code

I intend to fix the specific bugs that were reported, and will try
very hard not to alter any other behavior, but my baseline is how
expand-file-name behaved before your changes, not how it behaves now
(which is wrong).