Computing a derivation for a profile

[Ricardo Wurmus]

Hi Guix,

I would like to compute a derivation for a profile specified by a
manifest.  I do not (yet) want to actually build that derivation.

This seems like a simple thing to do, but I haven’t been able to
accomplish this.  Here is one of the things I’ve tried in “guix repl”:

--8<---------------cut here---------------start------------->8---
(begin
  (use-modules (gnu packages) (guix) (guix profiles))
  (derivation-file-name
   (with-store s
     (run-with-store s
       (lower-object
        (profile
         (content
          (specifications->manifest
           (list "texlive-collection-latex"
                 "texlive-collection-latexextra"
                 "texlive-collection-latexrecommended"
                 "texlive-collection-fontsrecommended"
                 "texlive-pgf")))))))))
--8<---------------cut here---------------end--------------->8---

Unfortunately, lowering this profile object appears to invariably result
in substitutes for all these texlive packages to be downloaded, even
though I only want to get the derivation.

Am I doing something wrong here?  Is this supposed to work?  Is this a
regression?

-- 
Ricardo