bug#28156: Emacs quietly munges symlink contents

[Paul Eggert <eggert@cs.ucla.edu>]

Michael Albinus wrote:
>>> We have quoting for these cases.
>> Quoting does not work for these cases. If I try to rename a symlink to
>> the literal string '~eggert' on my machine, Emacs will misbehave as
>> described and there is no way to quote the string naming the symlink
>> to fix this.
> (make-symbolic-link "~/.emacs" "/:/tmp/~eggert") ...

That's not the problem I was referring to. Sorry, I should have given more 
detail. By "misbehave as described" I was referring to an earlier-mentioned 
scenario where rename-file copies because the source and destination are on 
different filesystems. For example, suppose the current directory is on a 
different filesystem from /tmp, and I execute the following in my *scratch* buffer:

(shell-command "ln -s '~' symlink")
0
(file-symlink-p "symlink")
"~"
(rename-file "symlink" "/tmp/symlink")
nil
(file-symlink-p "/tmp/symlink")
"/home/eggert"

Here, rename-file quietly expands the symlink contents, which is a bug. As far 
as I can see, one cannot work around the bug by using Tramp quoting; for 
example, (rename-file "/:symlink" "/:/tmp/symlink") does the same thing that 
(rename-file "symlink" "/tmp/symlink") does.