bug#28156: Emacs quietly munges symlink contents

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

Michael Albinus wrote:

> What about file-truename? I believe it still must quote the result,
> otherwise we run into problems. See
> 
> (make-symbolic-link "/x:y:" "/tmp/foo")
> (file-truename  "/tmp/foo")
> 
> The latter shall return "/:/x:y:" (as of today) instead of
> "/x:y:".

Thanks for catching that. While looking into it, I noticed that file-truename 
has long mishandled symlink contents starting with ~ as in the following example:

$ ln -s '~nosuchuser' /tmp/foo
$ ls -l /tmp/foo
lrwxrwxrwx. 1 eggert eggert 11 Aug 26 18:51 /tmp/foo -> ~nosuchuser
$ src/emacs -Q -batch -eval '(message "%S" (file-truename "/tmp/foo"))'
"/home/eggert/src/gnu/emacs/master-tmp/~nosuchuser"

I fixed both problems.

> Maybe we shall document it as well. Neither the docstring of
> `file-truename', nor the Lisp reference say something about.
Yes, the documentation could stand some improving here. I fixed it up a bit, 
though not in the file-truename area as I'm thinking we may need some more 
changes here and would like to cogitate about it first. I'll CC: you on any 
further bug reports in this area.

I rebased the patch to master which simplified it since I no longer had to worry 
about Tramp tests, and installed the result. Closing this bug report.