bug#10489: 24.0.92; dired-do-copy may create infinite directory hierarchy

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> so what is the state of this bug and what do you plan for this?

> As a reminder, we needed:

> 1) A function to compare filenames locally.
> 2) A tramp handler for this function.
> 3) A function to check if file1 is subdir of file2, locally also.
> 4) A tramp handler for this one also?

> We have more or less 1 and 3, need tramp handlers for them.

> What else is needed?

Just before we try and solve this problem the hard way:
I just tried:

   % ln -s erlang-otp erl
   % cp -r erl/lib erlang-otp/lib/inviso/

on my Debian system, and it told me "cp: impossible de créer un
répertoire (« erl/lib ») dans lui-même (« erlang-otp/lib/inviso/lib »)",
but note that it only told me so *after* performing the copy.
I.e. it only detected the problem when trying to make
erlang-otp/lib/inviso/lib/inviso/lib

So it seems that the coreutils guys have found it sufficient to detect
the inf-loop after the fact and interrupt the operation at that point
rather than to try and predict that the cp will loop and don't perform
it at all.
It might be easier to get a solution that catches all cases that way:
remember the name and identity (inode/file-attributes/younameit) of
the top directory we create, and whenever we're about to copy
a directory of the same name, check whether it happens to have the
same identity, in which case we've hit an inf-loop.


        Stefan