bug#31317: 26.1; Add a tramp-make-tramp-temp-file* variant which returns the full tramp filename?

[Phil Sainty]

I have a tramp use-case where I want to create a temporary file
on the remote host and then populate that file via elisp -- I am
using (with-temp-file tramp-file-name (insert contents)) -- and
`tramp-make-tramp-temp-file' doesn't seem to facilitate this
nicely due to it returning only the local part of the generated
filename, which means I need to *recreate* the full tramp path
for that file before I can edit the file.

At present I am using `tramp-make-tramp-file-name' using the
returned local path and the original vector passed to
`tramp-make-tramp-temp-file'; but as well as being cumbersome,
I don't like making the assumption that I'm always going to get
the correct value (even if it turns out that I would in practice).

(I should perhaps even be dissecting the return value of
`tramp-get-remote-tmpdir' to obtain a new vector to recreate
that full path with, but that's even more work, and it looks
like it would wind up being the same values...)

It would seem useful to split `tramp-make-tramp-temp-file' into
two functions; one to generate the temporary file and return the
full path, and the other to return the localname.

Does the following seem reasonable?


(defun tramp-make-tramp-temp-file (vec)
  "Create a temporary file on the remote host identified by VEC.
Return the local name of the temporary file."
  (with-parsed-tramp-file-name (tramp-make-tramp-temp-file* vec)
      nil localname))

(defun tramp-make-tramp-temp-file* (vec)
  "Create a temporary file on the remote host identified by VEC.
Return the full tramp file name of the temporary file."
  (let ((prefix (expand-file-name
                 tramp-temp-name-prefix (tramp-get-remote-tmpdir vec)))
        result)
    (while (not result)
      ;; `make-temp-file' would be the natural choice for
      ;; implementation.  But it calls `write-region' internally,
      ;; which also needs a temporary file - we would end in an
      ;; infinite loop.
      (setq result (make-temp-name prefix))
      (if (file-exists-p result)
          (setq result nil)
        ;; This creates the file by side effect.
        (set-file-times result)
        (set-file-modes result (string-to-number "0700" 8))))
    result))



In GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll 
bars)
 of 2018-04-15 built on shodan
Windowing system distributor 'The X.Org Foundation', version 
11.0.11804000
System Description:     Ubuntu 16.04.4 LTS

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For information about GNU Emacs and the GNU system, type C-h C-a.
GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll 
bars) of 2018-04-15
uncompressing tramp.el.gz...done
Making completion list...

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