bug#28156: Emacs quietly munges symlink contents

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

Eli Zaretskii wrote:

>> (shell-command "ln -s '~' symlink")
>> 0
>> (file-symlink-p "symlink")
>> "~"
>> (rename-file "symlink" "/tmp/symlink")
>> nil
>> (file-symlink-p "/tmp/symlink")
>> "/home/eggert"
> 
> If this is the problem,

It's just one instance of the problem.

> then let's solve it without affecting
> make-symbolic-link.

This instance of the problem occurs because rename-file calls 
make-symbolic-link, and make-symbolic-link silently alters the link target. The 
real problem here is with make-symbolic-link: the rename-file bug is just a symptom.

>> 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.
> 
> But AFAIU, file-symlink-p can return a quoted name if its argument is
> quoted.

I don't know what you mean by "quoted". file-symlink-returns a string, and the 
string is supposed to be the contents of the symlink. file-symlink-p is working 
correctly here. It's make-symbolic-link (called from rename-file) that is 
screwing up.