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Re: copy-file with two remote files behaves strangely

From: Stefan Monnier
Subject: Re: copy-file with two remote files behaves strangely
Date: Tue, 14 Aug 2001 14:08:41 -0400

> >> From: address@hidden (Kai =?iso-8859-1?q?Gro=DFjohann?=)
> >> Date: Sun, 05 Aug 2001 13:43:22 +0200
> >> 
> >> I don't think that requiring filename patterns to be nonoverlapping
> >> is the right approach, anyway.
> > 
> > However, note that the current file-name-handler machinery is
> > _entirely_ based on this assumption.  Namely, the lookup for a handler
> > is based on regexp matching against the file's name, and thus
> > overlapping file-name patterns is generally a bad idea.  That is, you
> > are suggesting a significant change in how this feature works until
> > now.

Huh? jka-compr and ange-ftp patterns overlap rather happily.
As a matter of fact, I expect that overlapping patterns on file-name-handlers
are the rule more than the exception.

> The copy-file problem is the only problem with overlapping patterns
> that I've found so far.  For all the rest, Emacs takes the first
> matching entry in file-name-handler-alist, and that works nicely.  At
> least with Tramp and ange-ftp.

I think the best solution is for copy-file to do a bit more of the work:
if both files have a magic handler (and unless both have the same handler),
copy-file should use an intermediate /tmp file.

> Oh.  Maybe my message was a bit unclear.  Just getting tar to work is
> not the problem.  I think problems begin when several filename
> handlers apply to the same file.  Then the correct processing might
> depend on the order in which the handlers are invoked.  (Though who
> can tell for sure, it's not been done yet.)
> Hm.  Maybe I should try whether a gzipped file via ange-ftp works with
> jka-compr before ange-ftp in file-name-handler-alist as well as vice
> versa.

No need to try.  We already heard of problems of ordering between
jka-compr and Tramp, as well as between auto-image-file-mode and
jka (or was it ange-ftp).

I think that finding the right solution to the ordering problem will
require some work, to try and understand why it works one way and not
the other.


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