Re: Tramp and VC integration: "calling user"

[Andre Spiegel <spiegel@gnu.org>]

On Thu, 2005-03-31 at 08:34 -0500, Stefan Monnier wrote:

> Could you remind me why file-writable-p can't be used?

The conditions "file is writable by the calling user" and "file is
locked by the calling user" are not equivalent.  They can differ if
somebody modifies file permissions deliberately (I've seen this happen
at most sites where RCS is used).  They also differ if RCS is used with
non-strict locking.

VC has lots of code to detect mismatches between the two conditions,
because they do occur all the time in real world situations.  There is
also a special user option, vc-mistrust-permissions, which does
precisely what the name suggests.

So, in short, it is not possible to use file-writable-p.  There needs to
be a way, as Kai described, to compare the name of the calling user and
the name of the locking user as per the RCS master file.

I think the suggestion no. 2, file-calling-user, is best.  Conceptually,
it is something like "user-login-name relative to a given file".  For
files on the local machine, it is the name of the user running Emacs.
For files on a remote machine, it is the name of the user under which
the files are accessed (the login account at the remote machine).
Perhaps it would be worthwhile to add an optional FILE argument to
user-login-name, but it already has an optional argument, UID, so
perhaps a new function, file-calling-user, as Kai suggests, is best.