pack: Allow multiple '--manifest' options.

* guix/scripts/pack.scm (guix-pack): Collect 'manifest' options, and
concatenate the resulting manifests.
* tests/guix-pack.sh: Test it.
* doc/guix.texi (Invoking guix pack): Document it.

doc/guix.texi

@@ -5178,7 +5178,8 @@ build} (@pxref{Additional Build Options, @code{--expression} in
 @item --manifest=@var{file}
 @itemx -m @var{file}
 Use the packages contained in the manifest object returned by the Scheme
-code in @var{file}.
+code in @var{file}.  This option can be repeated several times, in which
+case the manifests are concatenated.
 
 This has a similar purpose as the same-named option in @command{guix
 package} (@pxref{profile-manifest, @option{--manifest}}) and uses the

guix/scripts/pack.scm

@@ -965,7 +965,10 @@ (define (manifest-from-args store opts)
                                   (list (transform store package) "out")))
                                (reverse
                                 (filter-map maybe-package-argument opts))))
-           (manifest-file (assoc-ref opts 'manifest)))
+           (manifests     (filter-map (match-lambda
+                                        (('manifest . file) file)
+                                        (_ #f))
+                                      opts)))
       (define properties
         (if (assoc-ref opts 'save-provenance?)
             (lambda (package)
@@ -979,11 +982,15 @@ (define properties
             (const '())))
 
       (cond
-       ((and manifest-file (not (null? packages)))
+       ((and (not (null? manifests)) (not (null? packages)))
         (leave (G_ "both a manifest and a package list were given~%")))
-       (manifest-file
-        (let ((user-module (make-user-module '((guix profiles) (gnu)))))
-          (load* manifest-file user-module)))
+       ((not (null? manifests))
+        (concatenate-manifests
+         (map (lambda (file)
+                (let ((user-module (make-user-module
+                                    '((guix profiles) (gnu)))))
+                  (load* file user-module)))
+              manifests)))
        (else
         (manifest
          (map (match-lambda

tests/guix-pack.sh

@@ -109,3 +109,14 @@ drv1="`guix pack -n guile 2>&1 | grep pack.*\.drv`"
 drv2="`guix pack -n --with-source=guile=$test_directory guile 2>&1 | grep pack.*\.drv`"
 test -n "$drv1"
 test "$drv1" != "$drv2"
+
+# Try '--manifest' options.
+cat > "$test_directory/manifest1.scm" <<EOF
+(specifications->manifest '("guile"))
+EOF
+cat > "$test_directory/manifest2.scm" <<EOF
+(specifications->manifest '("emacs"))
+EOF
+drv="`guix pack -nd -m "$test_directory/manifest1.scm" -m "$test_directory/manifest2.scm"`"
+guix gc -R "$drv" | grep `guix build guile -nd`
+guix gc -R "$drv" | grep `guix build emacs -nd`