bug#32844: Allow profiles to be instantiated from a profile's "manifest" file

[Ludovic Courtès]

Hello Guix,

Quoth <https://gnunet.org/bot/log/guix/2016-05-27>:

--8<---------------cut here---------------start------------->8---
<alezost> I think it's impossible to use ~/.guix-profile/manifest for "guix 
package --manifest"                                                             
  
<civodul> ah yes, we cannot convert an instantiated profile into source (where 
"source" is the thing that one passes to --manifest)                           
<civodul> but we could/should have an option to allow:                          
                                                                              
<civodul> guix package -X ~someone/.guix-profile/manifest                       
                                                                              
<civodul> guix package -Y /gnu/store/...-profile.drv                            
                                                                              
<civodul> so people could simply carry over these things                        
                                                                              
<civodul> also: guix package -W /gnu/store/...-profile                          
                                                                              
<civodul> all these are quite easy to implement                                 
                                                                              
--8<---------------cut here---------------end--------------->8---

Ludo’.