Sanjoy Mahajan <sanjoy@olin.edu> writes:

>
> (require 'gnus-alias)
> (gnus-alias-init)
> ;;; upstream version checks just for message-mode, but notmuch uses
> ;;; notmuch-message-mode, which is derived from message-mode
> (defun gnus-alias-ensure-message-mode ()
>   "Assert that the current buffer is a message buffer."
>   (when (not (derived-mode-p 'notmuch-message-mode))
>     (gnus-alias-error "Must be in `message-mode' or mode derived from it. ")))
> (add-hook 'message-setup-hook 'gnus-alias-determine-identity)

Maybe upstream Emacs would accept something like that if it says
"(derived-mode-p 'message-mode)".

d