guix package: Display generation diffs.

* guix/ui.scm (display-profile-content-diff): New variable.
* guix/scripts/package.scm (process-query): Use display-profile-content-diff.

In collaboration with Benz Schenk.

guix/scripts/package.scm

@@ -3,6 +3,8 @@
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
 ;;; Copyright © 2013, 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2014, 2016 Alex Kost <alezost@gmail.com>
+;;; Copyright © 2016 Roel Janssen <roel@gnu.org>
+;;; Copyright © 2016 Benz Schenk <benz.schenk@uzh.ch>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -667,24 +669,30 @@ (define (process-query opts)
                      ((head tail ...) head))))
     (match (assoc-ref opts 'query)
       (('list-generations pattern)
-       (define (list-generation number)
+       (define (list-generation display-function number)
          (unless (zero? number)
            (display-generation profile number)
-           (display-profile-content profile number)
+           (display-function profile number)
            (newline)))
-
+       (define (diff-profiles profile numbers)
+         (unless (null-list? (cdr numbers))
+           (display-profile-content-diff profile (car numbers) (cadr numbers))
+           (diff-profiles profile (cdr numbers))))
        (cond ((not (file-exists? profile))      ; XXX: race condition
               (raise (condition (&profile-not-found-error
                                  (profile profile)))))
              ((string-null? pattern)
-              (for-each list-generation (profile-generations profile)))
+              (list-generation display-profile-content
+                               (car (profile-generations profile)))
+              (diff-profiles profile (profile-generations profile)))
              ((matching-generations pattern profile)
               =>
               (lambda (numbers)
                 (if (null-list? numbers)
                     (exit 1)
                     (leave-on-EPIPE
-                     (for-each list-generation numbers)))))
+                     (list-generation display-profile-content (car numbers))
+                     (diff-profiles profile numbers)))))
              (else
               (leave (_ "invalid syntax: ~a~%")
                      pattern)))

guix/ui.scm

@@ -7,6 +7,8 @@
 ;;; Copyright © 2014, 2015 Alex Kost <alezost@gmail.com>
 ;;; Copyright © 2015 David Thompson <davet@gnu.org>
 ;;; Copyright © 2015, 2016 Mathieu Lirzin <mthl@gnu.org>
+;;; Copyright © 2016 Roel Janssen <roel@gnu.org>
+;;; Copyright © 2016 Benz Schenk <benz.schenk@uzh.ch>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -87,6 +89,7 @@ (define-module (guix ui)
             matching-generations
             display-generation
             display-profile-content
+            display-profile-content-diff
             roll-back*
             switch-to-generation*
             delete-generation*
@@ -1070,6 +1073,31 @@ (define (display-generation profile number)
           (format #t (_ "~a\t(current)~%") header)
           (format #t "~a~%" header)))))
 
+(define (display-profile-content-diff profile gen1 gen2)
+  "Display the changed packages in PROFILE GEN2 compared to generation GEN2."
+
+  (define (equal-entry? first second)
+    (string= (manifest-entry-item first) (manifest-entry-item second)))
+
+  (define (display-entry entry prefix)
+    (match entry
+      (($ <manifest-entry> name version output location _)
+       (format #t " ~a ~a\t~a\t~a\t~a~%" prefix name version output location))))
+
+  (define (list-entries number)
+    (manifest-entries (profile-manifest (generation-file-name profile number))))
+
+  (define (display-diff profile old new)
+    (display-generation profile new)
+    (let ((added (lset-difference
+                  equal-entry? (list-entries new) (list-entries old)))
+          (removed (lset-difference
+                    equal-entry? (list-entries old) (list-entries new))))
+      (for-each (cut display-entry <> "+") added)
+      (for-each (cut display-entry <> "-") removed)))
+
+  (display-diff profile gen1 gen2))
+
 (define (display-profile-content profile number)
   "Display the packages in PROFILE, generation NUMBER, in a human-readable
 way."