emacs/notmuch-wash.el: Add `notmuch-wash-convert-inline-patch-to-part'.

Detect inline patches and convert them to fake attachments, in order
that `diff-mode' highlighting can be applied to the patch. This can be
enabled by customising `notmuch-show-insert-text/plain-hook'.

emacs/notmuch-show.el

@@ -71,7 +71,8 @@ any given message."
   "Functions used to improve the display of text/plain parts."
   :group 'notmuch
   :type 'hook
-  :options '(notmuch-wash-wrap-long-lines
+  :options '(notmuch-wash-convert-inline-patch-to-part
+	     notmuch-wash-wrap-long-lines
 	     notmuch-wash-tidy-citations
 	     notmuch-wash-elide-blank-lines
 	     notmuch-wash-excerpt-citations))

emacs/notmuch-wash.el

@@ -23,6 +23,8 @@
 
 (require 'coolj)
 
+(declare-function notmuch-show-insert-bodypart "notmuch-show" (msg part depth)
+
 ;;
 
 (defvar notmuch-wash-signature-regexp
@@ -231,4 +233,40 @@ When doing so, maintaining citation leaders in the wrapped text."
 
 ;;
 
+(require 'diff-mode)
+
+(defvar diff-file-header-re) ; From `diff-mode.el'.
+
+(defun notmuch-wash-convert-inline-patch-to-part (depth)
+  "Convert an inline patch into a fake 'text/x-diff' attachment.
+
+Given that this function guesses whether a buffer includes a
+patch and then guesses the extent of the patch, there is scope
+for error."
+
+  (goto-char (point-min))
+  (if (re-search-forward diff-file-header-re nil t)
+      (progn
+	(beginning-of-line -1)
+	(let ((patch-start (point))
+	      (patch-end (point-max))
+	      part)
+	  (goto-char patch-start)
+	  (if (or
+	       ;; Patch ends with signature.
+	       (re-search-forward notmuch-wash-signature-regexp nil t)
+	       ;; Patch ends with bugtraq comment.
+	       (re-search-forward "^\\*\\*\\* " nil t))
+	      (setq patch-end (match-beginning 0)))
+	  (save-restriction
+	    (narrow-to-region patch-start patch-end)
+	    (setq part (plist-put part :content-type "text/x-diff"))
+	    (setq part (plist-put part :content (buffer-string)))
+	    (setq part (plist-put part :id -1))
+	    (setq part (plist-put part :filename "inline patch"))
+	    (delete-region (point-min) (point-max))
+	    (notmuch-show-insert-bodypart nil part depth))))))
+
+;;
+
 (provide 'notmuch-wash)