bug#28156: Emacs quietly munges symlink contents

[Eli Zaretskii]

> Cc: michael.albinus@gmx.de, p.stephani2@gmail.com, 28156@debbugs.gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 21 Aug 2017 01:34:20 -0700
> 
> The proposed change to file-symlink-p doesn't affect support for file name 
> quoting in its argument string. All it affects is the returned string. There 
> is 
> no need for it to quote the returned string

What if readlink returns a name such as "/ssh:foo@bar:/quux"?  A
symlink cannot have a remote file name as its target, can it?  So
quoting it sounds like a good way to avoid triggering a slow and
erroneous connection to some possibly non-existent host.  If we don't
quote, the caller might be in for a surprise.

> just as there is no need for read-file-name to quote the string that
> it returns.

read-file-name gets the string from the user, so it's an entirely
different context.  In that context, it's user's responsibility to
quote the file name if needed.

> Neither function is documented to quote its return value, and
> neither should do so.

Documentation in Emacs was never 110% accurate, so reading it as a
kind of formal requirements is not a good idea, IME.  This behavior is
in file-symlink-p since more than 17 years ago, so it's a de-facto
standard by now; if we decide it is what we want, we could document it
and move on.