[bug#66296] [PATCH v2] pack: Allow setting a custom image tag for Docker images

[soeren@soeren-tempel.net]

From: Sören Tempel <soeren@soeren-tempel.net>

Previously, the image repository name was automatically computed from
the packages in the manifest without allowing the user to set a custom
one. As such, changing the packages in the manifest would result in a
new image name. Thereby requiring updating documentation et cetera when
using `docker load` directory on the resulting image.

Inspired by `docker build -t`, this commit adds a new Docker-specific
option to `guix pack` which allows setting a custom repository name for
the resulting image. If this option is not specified, pack falls back
to computing the name from the manifest. Therefore, this change is
entirely backwards compatible.

* guix/scripts/pack.scm (guix-pack): add --image-tag option
* guix/scripts/pack.scm (%docker-format-options): new constant
* guix/scripts/pack.scm (show-docker-format-options): new procedure
* guix/scripts/pack.scm (show-docker-format-options/detailed): new procedure
* guix/scripts/pack.scm (docker-image): allow setting a custom
  repository name for the created docker image via extra-options.
* doc/guix.texi (Invoking guix pack)[docker]: Document --image-tag option

Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
---
Changes since v1: Document the new --image-tag and --help-docker-format
options in the Guix manual (Invoking guix pack).

 doc/guix.texi         |  9 ++++--
 guix/scripts/pack.scm | 66 ++++++++++++++++++++++++++++++-------------
 2 files changed, 52 insertions(+), 23 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 8c5697589f..b9b45cfe9d 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -7314,9 +7314,12 @@ specified binaries and symlinks.
 @item docker
 This produces a tarball that follows the
 @uref{https://github.com/docker/docker/blob/master/image/spec/v1.2.md,
-Docker Image Specification}.  The ``repository name'' as it appears in
-the output of the @command{docker images} command is computed from
-package names passed on the command line or in the manifest file.
+Docker Image Specification}.  By default, the ``repository name'' as it
+appears in the output of the @command{docker images} command is computed
+from package names passed on the command line or in the manifest file.
+Alternatively, the ``repository name'' can also be configured via the
+@option{--image-tag} option.  Refer to @option{--help-docker-format} for
+more information on such advanced options.
 
 @item squashfs
 This produces a SquashFS image containing all the specified binaries and
diff --git a/guix/scripts/pack.scm b/guix/scripts/pack.scm
index 01995c48b7..e7005e7bc6 100644
--- a/guix/scripts/pack.scm
+++ b/guix/scripts/pack.scm
@@ -507,7 +507,7 @@ (define* (docker-image name profile
 image is a tarball conforming to the Docker Image Specification, compressed
 with COMPRESSOR.  It can be passed to 'docker load'.  If TARGET is true, it
 must a be a GNU triplet and it is used to derive the architecture metadata in
-the image."
+the image.  EXTRA-OPTIONS may contain the IMAGE-TAG keyword argument."
   (define database
     (and localstatedir?
          (file-append (store-database (list profile))
@@ -531,7 +531,7 @@ (define build
                          (guix build utils)
                          (guix profiles) (guix search-paths)
                          (srfi srfi-1) (srfi srfi-19)
-                         (ice-9 match))
+                         (ice-9 match) (ice-9 optargs))
 
             #$(procedure-source manifest->friendly-name)
 
@@ -560,23 +560,26 @@ (define directives
 
             (setenv "PATH" #+(file-append archiver "/bin"))
 
-            (build-docker-image #$output
-                                (map store-info-item
-                                     (call-with-input-file "profile"
-                                       read-reference-graph))
-                                #$profile
-                                #:repository (manifest->friendly-name
-                                              (profile-manifest #$profile))
-                                #:database #+database
-                                #:system (or #$target %host-type)
-                                #:environment environment
-                                #:entry-point
-                                #$(and entry-point
-                                       #~(list (string-append #$profile "/"
-                                                              #$entry-point)))
-                                #:extra-files directives
-                                #:compressor #+(compressor-command compressor)
-                                #:creation-time (make-time time-utc 0 1))))))
+            (let-keywords '#$extra-options #f
+                          ((image-tag #f))
+              (build-docker-image #$output
+                                  (map store-info-item
+                                       (call-with-input-file "profile"
+                                         read-reference-graph))
+                                  #$profile
+                                  #:repository (or image-tag
+                                                   (manifest->friendly-name
+                                                     (profile-manifest #$profile)))
+                                  #:database #+database
+                                  #:system (or #$target %host-type)
+                                  #:environment environment
+                                  #:entry-point
+                                  #$(and entry-point
+                                         #~(list (string-append #$profile "/"
+                                                                #$entry-point)))
+                                  #:extra-files directives
+                                  #:compressor #+(compressor-command compressor)
+                                  #:creation-time (make-time time-utc 0 1)))))))
 
   (gexp->derivation (string-append name ".tar"
                                    (compressor-extension compressor))
@@ -1287,6 +1290,20 @@ (define (required-option symbol)
                    (alist-cons symbol arg result)
                    rest))))
 
+(define %docker-format-options
+  (list (required-option 'image-tag)))
+
+(define (show-docker-format-options)
+  (display (G_ "
+      --help-docker-format  list options specific to the docker format")))
+
+(define (show-docker-format-options/detailed)
+  (display (G_ "
+      --image-tag=NAME
+                         Use the given NAME for the Docker image repository"))
+  (newline)
+  (exit 0))
+
 (define %deb-format-options
   (list (required-option 'control-file)
         (required-option 'postinst-file)
@@ -1407,6 +1424,10 @@ (define %options
                  (lambda (opt name arg result)
                    (alist-cons 'bootstrap? #t result)))
 
+         (option '("help-docker-format") #f #f
+                 (lambda args
+                   (show-docker-format-options/detailed)))
+
          (option '("help-deb-format") #f #f
                  (lambda args
                    (show-deb-format-options/detailed)))
@@ -1415,7 +1436,8 @@ (define %options
                  (lambda args
                    (show-rpm-format-options/detailed)))
 
-         (append %deb-format-options
+         (append %docker-format-options
+                 %deb-format-options
                  %rpm-format-options
                  %transformation-options
                  %standard-build-options
@@ -1433,6 +1455,7 @@ (define (show-help)
   (newline)
   (show-transformation-options-help)
   (newline)
+  (show-docker-format-options)
   (show-deb-format-options)
   (show-rpm-format-options)
   (newline)
@@ -1586,6 +1609,9 @@ (define (process-file-arg opts name)
                                       manifest)))
                    (pack-format (assoc-ref opts 'format))
                    (extra-options (match pack-format
+                                    ('docker
+                                     (list #:image-tag
+                                           (assoc-ref opts 'image-tag)))
                                     ('deb
                                      (list #:control-file
                                            (process-file-arg opts 'control-file)