scripts: environment: Allow lists of packages in expressions.

* guix/scripts/environment.scm (options/resolve-packages): Match against
  lists of packages when evaluating expressions.
* tests/guix-environment.sh: Add test.
* doc/guix.texi ("invoking guix environment"): Add docs.

doc/guix.texi

@@ -4730,7 +4730,8 @@ The available options are summarized below.
 @table @code
 @item --expression=@var{expr}
 @itemx -e @var{expr}
-Create an environment for the package that @var{expr} evaluates to.
+Create an environment for the package or list of packages that
+@var{expr} evaluates to.
 
 For example, running:
 
@@ -4741,10 +4742,18 @@ guix environment -e '(@@ (gnu packages maths) petsc-openmpi)'
 starts a shell with the environment for this specific variant of the
 PETSc package.
 
+Running:
+
+@example
+guix environment --ad-hoc -e '(@ (gnu) %base-packages)'
+@end example
+
+starts a shell with all the GuixSD base packages available.
+
 @item --load=@var{file}
 @itemx -l @var{file}
-Create an environment for the package that the code within @var{file}
-evaluates to.
+Create an environment for the package or list of packages that the code
+within @var{file} evaluates to.
 
 As an example, @var{file} might contain a definition like this
 (@pxref{Defining Packages}):

guix/scripts/environment.scm

@@ -253,6 +253,18 @@ (define (compact lst)
 (define (options/resolve-packages opts)
   "Return OPTS with package specification strings replaced by actual
 packages."
+  (define (package->outputs package mode)
+    (map (lambda (output)
+           (list mode package output))
+         (package-outputs package)))
+
+  (define (packages->outputs packages mode)
+    (match packages
+      ((? package? package)
+       (package->outputs package mode))
+      (((? package? packages) ...)
+       (append-map (cut package->outputs <> mode) packages))))
+
   (compact
    (append-map (match-lambda
                  (('package mode (? string? spec))
@@ -261,17 +273,11 @@ (define (options/resolve-packages opts)
                     (list (list mode package output))))
                  (('expression mode str)
                   ;; Add all the outputs of the package STR evaluates to.
-                  (match (read/eval str)
-                    ((? package? package)
-                     (map (lambda (output)
-                            (list mode package output))
-                          (package-outputs package)))))
+                  (packages->outputs (read/eval str) mode))
                  (('load mode file)
                   ;; Add all the outputs of the package defined in FILE.
-                  (let ((package (load* file (make-user-module '()))))
-                    (map (lambda (output)
-                           (list mode package output))
-                         (package-outputs package))))
+                  (let ((module (make-user-module '())))
+                    (packages->outputs (load* file module) mode)))
                  (_ '(#f)))
                opts)))
 

tests/guix-environment.sh

@@ -111,4 +111,15 @@ then
     grep -E '^export CPATH=.*-gcc-bootstrap-0/include'      "$tmpdir/a"
     grep -E '^export CPATH=.*-glibc-bootstrap-0/include'    "$tmpdir/a"
     grep -E '^export LIBRARY_PATH=.*-glibc-bootstrap-0/lib' "$tmpdir/a"
+
+    # Make sure a package list can be used with -e.
+    expr_list_test_code="
+(list (@@ (gnu packages commencement) gnu-make-boot0)
+      (@ (gnu packages bootstrap) %bootstrap-guile))"
+
+    guix environment --ad-hoc --no-substitutes --search-paths --pure \
+         -e "$expr_list_test_code" > "$tmpdir/a"
+
+    grep -E '^export PATH=.*-make-boot0-4.1/bin'      "$tmpdir/a"
+    grep -E '^export PATH=.*-guile-bootstrap-2.0/bin' "$tmpdir/a"
 fi