On Mon, 06 Mar 2017 17:04:18 +0100
ludo@gnu.org (Ludovic Courtès) wrote:

> Sergei Trofimovich <slyfox@inbox.ru> skribis:
> 
> >> Question time:
> >> 
> >> - Is there a way to run 'guix environment --target=' in the same way as 'guix build --target='
> >>   sets it up? I'd like to see how both compilers are supposed to be present in there.
> >>
> >> - Why default g++ in PATH is the host g++ and not target g++?
> >>   Target seems to make most sense if no explicit compiler is specified.
> >> 
> >> - How to actually set CXX to point to target g++?
> >>   It looks like implicitly there already both host (through native-inputs)
> >>   and target (through build-inputs) compilers available.
> >>   I would expect something like
> >>       #:make-flags (list (string-append "CXX=" <.?.>)) 
> >>   What should be in place of that "<.?.>" to refer to target g++?  
> >
> > I think I've found a workaround at least for my third question.
> >
> > Both host and target compilers are available as g++ and ${target}-g++.
> >
> > Thus the following workaround seems to work:
> >
> > diff --git a/gnu/packages/regex.scm b/gnu/packages/regex.scm
> > index f04cba706..a8fa689ab 100644
> > --- a/gnu/packages/regex.scm
> > +++ b/gnu/packages/regex.scm
> > @@ -20,11 +20,13 @@
> >
> >  (define-module (gnu packages regex)
> >    #:use-module ((guix licenses) #:prefix license:)
> >    #:use-module (guix packages)
> >    #:use-module (guix download)
> > -  #:use-module (guix build-system gnu))
> > +  #:use-module (guix build-system gnu)
> > +  #:use-module (guix utils) ; for %current-target-system
> > +  )
> >
> >  (define-public re2
> >     (package
> >       (name "re2")
> >       (version "2017-01-01")
> > @@ -40,11 +42,15 @@
> >                   "0yij1ajh66h3pj3kfz7y0ldrsww8rlpjzaavyr5lchl98as1jq74"))))
> >       (build-system gnu-build-system)
> >       (arguments
> >        `(#:test-target "test"
> >          ;; There is no configure step, but the Makefile respects a prefix.
> > -        #:make-flags (list (string-append "prefix=" %output))
> > +        #:make-flags (list (string-append "prefix=" %output)
> > +                           (string-append "CXX=" ,(string-append (if (%current-target-system)
> > +                                                                     (string-append (%current-target-system) "-")
> > +                                                                     "")
> > +                                                                 "g++")))  
> 
> As John wrote, this is the right fix for this package.

Aha!

> If you can send it with ‘git send-email’ (see
> <https://www.gnu.org/software/guix/manual/html_node/Submitting-Patches.html>),

Sent as:
    http://debbugs.gnu.org/cgi/bugreport.cgi?bug=26004

About the 'guix environment --target=' / 'guix build --target=' part or question:

Would it make sense to have '--target=' support in 'guix environment' tool or is it
too tricky?

Thanks!

-- 

  Sergei