bug#34834: 26.1; Remote `eshell/mv' and `eshell/cp' on Windows: Opening output file: Invalid argument, c:/home/ ...

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Date: Thu, 28 Mar 2019 18:44:09 +0100
> Cc: 34834@debbugs.gnu.org
> 
> --8<---------------cut here---------------start------------->8---
> C-x C-f /plinkx:detlefx:/home/albinus/ ;; This is a remote GNU/Linux machine.
> 
> M-: (expand-file-name "123" "tmp/") ;; 123 is a file, tmp is a directory 
> there.
> 
> => "c:/plinkx:detlefx:/home/albinus/tmp/123"
> --8<---------------cut here---------------end--------------->8---
> 
> I have added traces to this, with M-x trace-function-background for
> expand-file-name, tramp-sh-handle-expand-file-name, and
> tramp-file-name-handler. The latter function is Tramp's outmost
> function. The traces look like this:
> 
> ======================================================================
> 1 -> (expand-file-name "123" "tmp/")
> | 2 -> (tramp-file-name-handler expand-file-name "tmp/" 
> "/plinkx:detlefx:/home/albinus/")
> | | 3 -> (tramp-sh-handle-expand-file-name "tmp/" 
> "/plinkx:detlefx:/home/albinus/")
> | | | 4 -> (tramp-file-name-handler file-name-as-directory 
> "/plinkx:detlefx:/home/albinus/")
> | | | 4 <- tramp-file-name-handler: "/plinkx:detlefx:/home/albinus/"
> | | | 4 -> (expand-file-name "/home/albinus/tmp/")
> | | | 4 <- expand-file-name: "c:/home/albinus/tmp/"
> | | 3 <- tramp-sh-handle-expand-file-name: 
> "/plinkx:detlefx:/home/albinus/tmp/"
> | 2 <- tramp-file-name-handler: "/plinkx:detlefx:/home/albinus/tmp/"
> 1 <- expand-file-name: "c:/plinkx:detlefx:/home/albinus/tmp/123"
> ======================================================================
> 
> Looks, like Tramp returns the proper value 
> "/plinkx:detlefx:/home/albinus/tmp/",
> and then in its way through expand-file-name the drive letter is
> added. Since this is a C function, I'm not able to debug further.
> 
> Eli, could you pls check this?

I don't think I understand what should I check.  In general a file
name like "/foo/bar" will have a drive letter added to it by
expand-file-name.  What makes this case special?