environment: Add --manifest option.

* guix/scripts/environment.scm (show-help, %options): Add -m/--manifest.
(options/resolve-packages): Handle manifests.
* tests/guix-envronment.sh: Add a test.
* doc/guix.texi (Invoking guix environment): Document it.

doc/guix.texi

@@ -7231,6 +7231,15 @@ As an example, @var{file} might contain a definition like this
 @verbatiminclude environment-gdb.scm
 @end example
 
+@item --manifest=@var{file}
+@itemx -m @var{file}
+Create an environment for the packages contained in the manifest object
+returned by the Scheme code in @var{file}.
+
+This is similar to the same-named option in @command{guix package}
+(@pxref{profile-manifest, @option{--manifest}}) and uses the same
+manifest files.
+
 @item --ad-hoc
 Include all specified packages in the resulting environment, as if an
 @i{ad hoc} package were defined with them as inputs.  This option is

guix/scripts/environment.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014, 2015 David Thompson <davet@gnu.org>
+;;; Copyright © 2014, 2015, 2018 David Thompson <davet@gnu.org>
 ;;; Copyright © 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -141,6 +141,8 @@ COMMAND or an interactive shell in that environment.\n"))
   (display (G_ "
   -l, --load=FILE        create environment for the package that the code within
                          FILE evaluates to"))
+  (display (G_ "
+  -m, --manifest=FILE    create environment with the manifest from FILE"))
   (display (G_ "
       --ad-hoc           include all specified packages in the environment instead
                          of only their inputs"))
@@ -220,6 +222,11 @@ COMMAND or an interactive shell in that environment.\n"))
                    (alist-cons 'expression
                                (tag-package-arg result arg)
                                result)))
+         (option '(#\m "manifest") #t #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'manifest
+                               arg
+                               result)))
          (option '("ad-hoc") #f #f
                  (lambda (opt name arg result)
                    (alist-cons 'ad-hoc? #t result)))
@@ -286,6 +293,16 @@ packages."
       (((? package-or-package+output?) ...) ; many packages
        (map (cut package->output <> mode) packages))))
 
+  (define (manifest->outputs manifest)
+    (map (lambda (entry)
+           (cons 'ad-hoc-package ; manifests are implicitly ad-hoc
+                 (if (package? (manifest-entry-item entry))
+                     (list (manifest-entry-item entry)
+                           (manifest-entry-output entry))
+                     ;; Direct store paths have no output.
+                     (list (manifest-entry-item entry)))))
+         (manifest-entries manifest)))
+
   (compact
    (append-map (match-lambda
                  (('package mode (? string? spec))
@@ -299,6 +316,9 @@ packages."
                   ;; Add all the outputs of the package defined in FILE.
                   (let ((module (make-user-module '())))
                     (packages->outputs (load* file module) mode)))
+                 (('manifest . file)
+                  (let ((module (make-user-module '())))
+                    (manifest->outputs (load* file module))))
                  (_ '(#f)))
                opts)))
 

tests/guix-environment.sh

@@ -62,6 +62,15 @@ fi
 guix environment --bootstrap --ad-hoc guile-bootstrap --pure \
      -- "$SHELL" -c 'test -f "$GUIX_ENVIRONMENT/bin/guile"'
 
+# Make sure 'GUIX_ENVIRONMENT' points to the profile when building from a
+# manifest.
+echo "(use-modules (guix profiles) (gnu packages bootstrap))
+
+(packages->manifest (list %bootstrap-guile))
+" > $tmpdir/manifest.scm
+guix environment --bootstrap --manifest=$tmpdir/manifest.scm --pure \
+     -- "$SHELL" -c 'test -f "$GUIX_ENVIRONMENT/bin/guile"'
+
 # Make sure '-r' works as expected.
 rm -f "$gcroot"
 expected="`guix environment --bootstrap --ad-hoc guile-bootstrap \