guix/etc/snippets/text-mode/guix-commit-message-update-package

# -*- mode: snippet -*-
# name: guix-commit-message-update-package
# key: update
# condition: git-commit-mode
# --

gnu: ${1:`(with-temp-buffer
           (magit-git-wash #'magit-diff-wash-diffs
             "diff" "--staged")
           (goto-char (point-min))
           (when (re-search-forward "^[ ]*(define-public \\(\\S-+\\)" nil 'noerror)
             (match-string-no-properties 1)))`}: Update to ${2:`(with-temp-buffer
    (magit-git-wash #'magit-diff-wash-diffs
      "diff" "--staged")
    (goto-char (point-min))
    (search-forward "name" nil 'noerror)
    (search-forward "+" nil 'noerror)   ; first change
    (when (and (search-forward "version " nil 'noerror)
               (looking-at-p "\""))
      (let ((end (save-excursion (search-forward "\")" nil 'noerror))))
        (when end
          (forward-char)
          (buffer-substring-no-properties (point) (- end 2))))))`}.

* `(car (magit-staged-files))` ($1): Update to $2.$0
`(mapconcat (lambda (file) (concat "* " file)) (cdr (magit-staged-files)) "\n")`