scripts: refresh: Support --list-dependent=packages.issue-58824

* guix/scripts/refresh.scm (%options)[list-dependent]: Allow an
  optional argument.  Set 'LIST-DEPENDENT-MACHINE-READABLE? to
  #T in RESULT if the argument is "packages".
(list-dependents): Support #:MACHINE-READABLE?.
(guix-refresh): Pass #:MACHINE-READABLE? #T to LIST-DEPENDENTS if
'LIST-DEPENDENT-MACHINE-READABLE? is #T.
* doc/guix.texi: Document 'guix refresh --list-dependent=packages'.

2 files changed, 49 insertions, 26 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 1eb47e31cf..680666b58b 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -14108,11 +14108,20 @@ be used when passing @command{guix refresh} one or more package names:
 
 @table @code
 
-@item --list-dependent
-@itemx -l
+@item --list-dependent[=packages]
+@itemx -l [packages]
 List top-level dependent packages that would need to be rebuilt as a
 result of upgrading one or more packages.
 
+If the option is called with the optional @code{packages} argument, it
+will display only the list of packages, without the header stating the
+number of packages that will be rebuilt.  This can be used to run
+commands such as this, which builds all the dependents of @code{gtk}:
+
+@example
+$ guix build $(guix refresh gtk -l packages)
+@end example
+
 @xref{Invoking guix graph, the @code{reverse-package} type of
 @command{guix graph}}, for information on how to visualize the list of
 dependents of a package.
diff --git a/guix/scripts/refresh.scm b/guix/scripts/refresh.scm
index 14329751f8..7c3f392a96 100644
--- a/guix/scripts/refresh.scm
+++ b/guix/scripts/refresh.scm
@@ -9,6 +9,7 @@
 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2020 Simon Tournier <zimon.toutoune@gmail.com>
 ;;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
+;;; Copyright © 2022 ( <paren@disroot.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -93,9 +94,12 @@
         (option '(#\e "expression") #t #f
                 (lambda (opt name arg result)
                   (alist-cons 'expression arg result)))
-        (option '(#\l "list-dependent") #f #f
+        (option '(#\l "list-dependent") #f #t
                 (lambda (opt name arg result)
-                  (alist-cons 'list-dependent? #t result)))
+                  (append `((list-dependent? . #t)
+                            (list-dependent-machine-readable?
+                             . ,(and arg (string=? arg "packages"))))
+                          result)))
         (option '(#\r "recursive") #f #f
                 (lambda (opt name arg result)
                   (alist-cons 'recursive? #t result)))
@@ -417,8 +421,10 @@ releases for ~a~%")
                  '()
                  #:select? (const #t)))           ;include hidden packages
 
-(define (list-dependents packages)
-  "List all the things that would need to be rebuilt if PACKAGES are changed."
+(define* (list-dependents packages #:key (machine-readable? #f))
+  "List all the things that would need to be rebuilt if PACKAGES are
+changed.  If MACHINE-READABLE? is #T, display only a list of packages,
+with no human-friendly extra text."
   ;; Using %BAG-NODE-TYPE is more accurate than using %PACKAGE-NODE-TYPE
   ;; because it includes implicit dependencies.
   (define (full-name package)
@@ -431,27 +437,31 @@ releases for ~a~%")
            (covering   (filter (lambda (node)
                                  (null? (edges node)))
                                dependents)))
-      (match dependents
-        (()
-         (format (current-output-port)
-                 (N_ "No dependents other than itself: ~{~a~}~%"
-                     "No dependents other than themselves: ~{~a~^ ~}~%"
-                     (length packages))
-                 (map full-name packages)))
-
-        ((x)
-         (format (current-output-port)
-                 (G_ "A single dependent package: ~a~%")
-                 (full-name x)))
-        (lst
-         (format (current-output-port)
-                 (N_ "Building the following ~d package would ensure ~d \
+      (if machine-readable?
+          (format (current-output-port)
+                  (G_ "~{~a~^ ~}~%")
+                  (map full-name covering))
+          (match dependents
+            (()
+             (format (current-output-port)
+                     (N_ "No dependents other than itself: ~{~a~}~%"
+                         "No dependents other than themselves: ~{~a~^ ~}~%"
+                         (length packages))
+                     (map full-name packages)))
+            ((x)
+             (format (current-output-port)
+                     (G_ "A single dependent package: ~a~%")
+                     (full-name x)))
+            (lst
+             (format (current-output-port)
+                     (N_ "Building the following ~d package would ensure ~d \
 dependent packages are rebuilt: ~{~a~^ ~}~%"
-                     "Building the following ~d packages would ensure ~d \
+                         "Building the following ~d packages would ensure ~d \
 dependent packages are rebuilt: ~{~a~^ ~}~%"
-                     (length covering))
-                 (length covering) (length dependents)
-                 (map full-name covering))))
+                         (length covering))
+                     (length covering) (length dependents)
+                     (map full-name covering)))))
+      
       (return #t))))
 
 (define (list-transitive packages)
@@ -528,6 +538,8 @@ all are dependent packages: ~{~a~^ ~}~%")
          (updaters        (options->updaters opts))
          (recursive?      (assoc-ref opts 'recursive?))
          (list-dependent? (assoc-ref opts 'list-dependent?))
+         (list-dependent-machine-readable?
+          (assoc-ref opts 'list-dependent-machine-readable?))
          (list-transitive? (assoc-ref opts 'list-transitive?))
          (key-download    (assoc-ref opts 'key-download))
 
@@ -543,7 +555,9 @@ all are dependent packages: ~{~a~^ ~}~%")
           (mlet %store-monad ((packages (options->packages opts)))
             (cond
              (list-dependent?
-              (list-dependents packages))
+              (list-dependents packages
+                               #:machine-readable?
+                               list-dependent-machine-readable?))
              (list-transitive?
               (list-transitive packages))
              (update?