guix package: '--search-paths' can report combined search paths.

Partly fixes <http://bugs.gnu.org/20255>.

* guix/scripts/package.scm (search-path-environment-variables): Change
  'profile' to 'profiles'; expect it to be a list.
  (display-search-paths): Likewise.
  (%default-options): Remove 'profile' entry.
  (%options) <--profile>: Keep previous values associated with 'profile'
  in RESULT.
  (guix-package)[process-actions, process-query]: Handle the possible
  lack of 'profile' pair in OPTS.

1 files changed, 14 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 896a8c8496..09a860a64f 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -1347,6 +1347,20 @@ meaning that the returned environment variable definitions will either
 be exact settings, or prefixes or suffixes of the current value of these
 variables.  When omitted, @var{kind} defaults to @code{exact}.
 
+This option can also be used to compute the @emph{combined} search paths
+of several profiles.  Consider this example:
+
+@example
+$ guix package -p foo -i guile
+$ guix package -p bar -i guile-json
+$ guix package -p foo -p bar --search-paths
+@end example
+
+The last command above reports about the @code{GUILE_LOAD_PATH}
+variable, even though, taken individually, neither @file{foo} nor
+@file{bar} would lead to that recommendation.
+
+
 @item --profile=@var{profile}
 @itemx -p @var{profile}
 Use @var{profile} instead of the user's default profile.