ui: Factorize `--version'.

* guix/ui.scm (show-version-and-exit): New procedure.
* guix-build.in (show-version): Remove.
  (%options)["version"]: Use `show-version-and-exit'.
* guix-download.in: Likewise.
* guix-package.in: Likewise.

guix-build.in

@@ -71,9 +71,6 @@ When SOURCE? is true, return the derivations of the package sources."
   `((system . ,(%current-system))
     (substitutes? . #t)))
 
-(define (show-version)
-  (display "guix-build (@PACKAGE_NAME@) @PACKAGE_VERSION@\n"))
-
 (define (show-help)
   (display (_ "Usage: guix-build [OPTION]... PACKAGE-OR-DERIVATION...
 Build the given PACKAGE-OR-DERIVATION and return their output paths.\n"))
@@ -113,8 +110,7 @@ Report bugs to: ~a.~%") "@PACKAGE_BUGREPORT@"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version)
-                  (exit 0)))
+                  (show-version-and-exit "guix-build")))
 
         (option '(#\S "source") #f #f
                 (lambda (opt name arg result)

guix-download.in

@@ -88,9 +88,6 @@ exec ${GUILE-@GUILE@} -L "@guilemoduledir@" -l "$0"    \
   ;; Alist of default option values.
   `((format . ,bytevector->nix-base32-string)))
 
-(define (show-version)
-  (display "guix-download (@PACKAGE_NAME@) @PACKAGE_VERSION@\n"))
-
 (define (show-help)
   (display (_ "Usage: guix-download [OPTION]... URL
 Download the file at URL, add it to the store, and print its store path
@@ -131,8 +128,7 @@ Report bugs to: ~a.~%") "@PACKAGE_BUGREPORT@"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version)
-                  (exit 0)))))
+                  (show-version-and-exit "guix-download")))))
 
 
 ;;;

guix-package.in

@@ -30,6 +30,7 @@ exec ${GUILE-@GUILE@} -L "@guilemoduledir@" -l "$0"    \
 ;;; along with Guix.  If not, see <http://www.gnu.org/licenses/>.
 
 (define-module (guix-package)
+  #:use-module (guix ui)
   #:use-module (guix store)
   #:use-module (guix derivations)
   #:use-module (guix packages)
@@ -192,9 +193,6 @@ all of PACKAGES, a list of name/version/output/path tuples."
     (format (current-error-port) fmt args ...)
     (exit 1)))
 
-(define (show-version)
-  (display "guix-package (@PACKAGE_NAME@) @PACKAGE_VERSION@\n"))
-
 (define (show-help)
   (display (_ "Usage: guix-package [OPTION]... PACKAGES...
 Install, remove, or upgrade PACKAGES in a single transaction.\n"))
@@ -228,8 +226,7 @@ Report bugs to: ~a.~%") "@PACKAGE_BUGREPORT@"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version)
-                  (exit 0)))
+                  (show-version-and-exit "guix-package")))
 
         (option '(#\i "install") #t #f
                 (lambda (opt name arg result)

guix/ui.scm

@@ -19,12 +19,14 @@
 (define-module (guix ui)
   #:use-module (guix utils)
   #:use-module (guix store)
+  #:use-module (guix config)
   #:use-module (guix packages)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:export (_
             N_
             leave
+            show-version-and-exit
             call-with-error-handling
             with-error-handling))
 
@@ -46,6 +48,12 @@
     (format (current-error-port) fmt args ...)
     (exit 1)))
 
+(define* (show-version-and-exit #:optional (command (car (command-line))))
+  "Display version information for COMMAND and `(exit 0)'."
+  (simple-format #t "~a (~a) ~a~%"
+                 command %guix-package-name %guix-version)
+  (exit 0))
+
 (define (call-with-error-handling thunk)
   "Call THUNK within a user-friendly error handler."
   (guard (c ((package-input-error? c)