Re: (concat "/dir/name/" "foo") --> (expand-file-name "foo" "/dir/name/")

[prj@po.cwru.edu (Paul Jarc)]

Dave Love <d.love@dl.ac.uk> writes:
>  PJ> In that case, expand-file-name won't necessarily give you the
>  PJ> file name you want.
> 
> I don't understand this.  It sounds like cause for a bug report.

Not with regard to the implementation of expand-file-name, but perhaps
with various uses of it.  Consider "foo/../bar".  expand-file-name
will normalize it to "bar", but it's possible that foo is a symlink to
something other than a sibling directory.  In that case, "foo/../bar"
and "bar" might *both* name existing files, but not the same file.  Or
one might name an existing file, and the other might not.  Which
string names the file we actually want?  In each particular case of
deciding whether to use expand-file-name, you have to decide which
file you would want: the file named literally by the string you've
got, or the file named by the string's expansion.  There is no general
answer; you have to decide case by case.  Also, you want to be careful
not to expand an already-expanded name, if expand-file-name is indeed
not necessarily idempotent.  Otherwise you'll be dealing with two
different filenames, when you really want to work with just one file.

>  PJ> Handlers aren't involved until I/O is attempted, AFAIK.
> 
> I believe the operations listed under Info (elisp)Magic File Names
> accurately reflect the code.  If not, please make a bug report.

I was probably mistaken there, then.  I can't find that node in my
manual, but the Index node is inaccessible, so maybe my manual is
broken.
#    This Info file contains edition 2.5 of the GNU Emacs Lisp Reference
# Manual, corresponding to GNU Emacs version 20.3.
or is there a newer manual?


paul