bug#10319: 24.0.92; doc string of `file-remote-p'

[Michael Albinus <michael.albinus@gmx.de>]

"Drew Adams" <drew.adams@oracle.com> writes:

>> The second sentence means that a relative filename like 
>> "/sudo::../../.." does not make sense, because it cannot
>> expand out of the "/sudo::" jail.
>
> So what are we trying to tell _users_ here?
> Is this what we are really trying to say?
>
>  FILE must be an absolute file name.
>
> If so, what should we say happens if you nevertheless pass a relative
> file name?  Return value is unspecified (could be nil or non-nil)?  An
> error is raised?  What should we tell users is the behavior?

Any relative filename cannot expand to a different remote connection, or
a filename of your local filesystem. But you are right, this information
is irrelevant for the docstring of `file-remote-p'.

>> > We should also perhaps say what "the complete 
>> > identification" is/means.  IOW, when IDENTIFICATION is nil,
>> > what can we say about the return value?
>> 
>> In that case, the returned string could make a local file 
>> name remote. We could always offer to apply
>>    (concat (file-remote-p "whatever") "local-file-name")
>> given that `concat' accepts nil as argument.
>
> Sorry, I just don't understand your reply to my question (what is the
> complete identification - what is returned if IDENTIFICATION is nil).
> Could you rephrase or elaborate?

When IDENTIFICATION is nil, the returned string is everything until the
last ":" (with expanded default method, default user, default host).

(file-remote-p "/sudo::/") => "/sudo:root@localhost:"

(file-remote-p "/localhost:/") => "/scpc:localhost:"

What I have tried to explain is a common technique for creation of new
remote filenames, derived from an existing one. Let's say you have a
variable `file' containing the remote filename "/sudo::/path/to/file",
and you want to create a new remote filename for the file "/bin/sh". You
apply then (concat (file-remote-p file) "/bin/sh")

> Thx - Drew

Best reards, Michael.