[bug#38441] [PATCH 5/5] guix system: Add "describe" action.

[Ludovic Courtès]

* guix/scripts/system.scm (show-help): Add "describe".
(process-command): Handle it.
(guix-system): Likewise.
* doc/guix.texi (Invoking guix system): Document it.
---
 doc/guix.texi           |  4 ++++
 guix/scripts/system.scm | 11 ++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 198792c54a..cb4b0b45e7 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -26240,6 +26240,10 @@ bootloader boot menu:
 
 @table @code
 
+@item describe
+Describe the current system generation: its file name, the kernel and
+bootloader used, etc., as well as provenance information when available.
+
 @item list-generations
 List a summary of each generation of the operating system available on
 disk, in a human-readable way.  This is similar to the
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index 0ddb40a03c..ccff68f1ab 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -921,6 +921,8 @@ Some ACTIONS support additional ARGS.\n"))
    reconfigure      switch to a new operating system configuration\n"))
   (display (G_ "\
    roll-back        switch to the previous operating system configuration\n"))
+  (display (G_ "\
+   describe         describe the current system\n"))
   (display (G_ "\
    list-generations list the system generations\n"))
   (display (G_ "\
@@ -1187,6 +1189,12 @@ argument list and OPTS is the option alist."
                       ((pattern) pattern)
                       (x (leave (G_ "wrong number of arguments~%"))))))
        (list-generations pattern)))
+    ((describe)
+     (match (generation-number %system-profile)
+       (0
+        (error (G_ "no system generation, nothing to describe~%")))
+       (generation
+        (display-system-generation generation))))
     ((search)
      (apply (resolve-subcommand "search") args))
     ;; The following commands need to use the store, but they do not need an
@@ -1226,7 +1234,8 @@ argument list and OPTS is the option alist."
           (case action
             ((build container vm vm-image disk-image reconfigure init
               extension-graph shepherd-graph
-              list-generations delete-generations roll-back
+              list-generations describe
+              delete-generations roll-back
               switch-generation search docker-image)
              (alist-cons 'action action result))
             (else (leave (G_ "~a: unknown action~%") action))))))
-- 
2.24.0