Export patches from Emacs' Notmuch

I’m reading several linux-kernel related mailing lists. They are full of proposed patches. And from time to time a few of them look interesting. So I wanted to have an easy (and fast) solution of exporting those patches: with a keystroke, and without the need of specifying patch names.

Format of a patch email

If you ever contributed a patch to Linux, you’d know that your patch must follow some formatting rules, or it might be ignored. Some of those rules are import for my purpose:

  • if a patch isn’t self, consistent, it should have some ¼ (1 of 4) marking in the subject
  • patches must have a [PATCH …] tag at the start of the subject.
  • patches must be directly in the e-mail text, not in an attachment. This effectively means that I don’t have to deal with MIME parts.

Here are two examples of such email subjects:

[PATCH] mmc: host: use pr_err for sdhci_dumpregs
[PATCH 3/9] clocksource/drivers/rockchip_timer: Convert init function to return error


Let’s define some local variables:

(defun my-notmuch-export-patch ()
  (let* ((from (notmuch-show-get-from))
         (date (notmuch-show-get-date))
         (subject (notmuch-show-get-subject))
         (id (notmuch-show-get-message-id))
         (filename subject)

The first step is to extract the patch number:

(when (string-match "\\[PATCH.+?0*\\([0-9]+\\)/[0-9]+\\]" filename)
  (setq patchnum (string-to-number (match-string 1 filename))))

We now do the following steps with the raw subject:

  • remove the optional [PATCH …] prefix
  • replace everything that are not letters/digits with a dash
  • convert consecutive dashes into one dash
  • make sure we don’t have a dash at the start
  • make sure we don’t have a dash at the end

So let’s do this:

(setq filename (replace-regexp-in-string "\\[PATCH.*\\]" "" filename))
(setq filename (replace-regexp-in-string "\[^a-zA-Z0-9]" "-" filename))
(setq filename (replace-regexp-in-string "\\-+" "-" filename))
(setq filename (replace-regexp-in-string "^-" "" filename))
(setq filename (replace-regexp-in-string "-$" "" filename))

Prepend the patchnum to the future filename:

(when patchnum
  (setq filename (concat (format "%04d" patchnum) "-" filename)))

And prepend a directory as well:

(setq filename (concat "/tmp/" filename ".patch"))

And now we need write things out.

First we create a temporary buffer and insert some of message properties as a header.

Then we need to get the actual patch. In a non-MIME-encoded e-mail, the text is the (sic!) MIME part 1. We call the notmuch binary to give us back this text and insert it into the buffer as well. Note: the t as the 3rd argument to (call-process makes the output of the notmuch command end in the current buffer.

Finally I write this buffer to a file and kill the buffer. buffer.

  (let ((buf (generate-new-buffer (concat "*notmuch-export-patch-" id "*"))))
    (with-current-buffer buf
      (insert (format "Subject: %s\n" subject))
      (insert (format "From: %s\n" from))
      (insert (format "Date: %s\n" date))
      (insert (format "Message-Id: %s\n\n" (substring id 3)))
      (let ((coding-system-for-read 'no-conversion))
        (call-process notmuch-command nil t nil "show" "--part:1" id))
      (write-file filename))
    (kill-buffer buf)))))



And the last step is to bind this to some keys. As the function works both in tree-view and in message-show mode, I bind it to both places.

(define-key notmuch-show-mode-map "x" #'my-notmuch-export-patch)
(define-key notmuch-tree-mode-map "x" #'my-notmuch-export-patch)