Re: file-relative-name and remote files

[Lars Hansen]

Richard Stallman wrote:

> Hmm, this raises the issue of what expand-file-name should do with
> "/foo:../..".  I guess it must leave that unchanged, which means that
> the expand-file-name handler for these file names should be rather
> careful in what it does to simplify whatever part of the name comes
> after.  It is not correct to simplify /X/../Y into /Y when /X
> is a remote prefix.
>  
I do not agree. Let me try to explain why.

One might describe ".." as "the parent directory". This makes good sense 
when files make up a tree, because in that case each file (except the 
root) has exactly one parent. However, as I mentioned earlier, files do 
not in general make up a tree, they make up a more general graph. A file 
might have more than one parent. An example is the file

 /foo:x

This file should be thought of as "the file x on the remote computer" as 
well as "the file "/foo:x" on the local computer. The file has (at 
least) two parents: The parent of x on the
remote computer and the parent of "/foo:x" on the local computer, i.e. 
the root on the local computer.

The fact that a file can have more than one parent is *not* special for 
the construct above. On a unix like system we have links. Consider the 
following example:

 galois:~/> mkdir y
 galois:~/> cd y
 galois:~/y/> mkdir x
 galois:~/y/> cd x
 galois:~/y/x/> ln -s ../x

Now the file x has two parents: y and itself! How does the system then 
decide what ".." should refer to? Take a look:

 galois:~/y/x/> cd x
 galois:~/y/x/x/> cd ..
 galois:~/y/x/> cd ..
 galois:~/y/>

We have a path to x, and ".." refers to the parent in that path. In the 
first "cd .." above ".." means x, in the second it means y.

In my opinion we should use the same strategy with remote files. Just as 
in the example above there is more than one path from a computer to the 
file y in my home directory on galois:

 /address@hidden:y
 /address@hidden:/home/l/larsh/y

In the first case ".." should refer to the root on the local machine, in 
the second case it should refer to the directory /home/l/larsh on the 
remote machine.

Thus I think that "/foo:../.." should refer to the root on the local 
machine (just like "/foo:bar/.." for any choice of "bar"). If you want 
to access files above the home directory on the remote machine, you 
should choose a path via the root on the remote machine.