Emacs collaborative buffers open in the wrong mode

Question

I am using Emacs and Rudel to collaborate with a remote programmer. Rudel has a concept of published buffers. When my partner publishes a buffer, I can subscribe to it and the we can both edit it simultaneously.

My problem is that when he publishes a Python file with a *.py extension and I subscribe to it, my buffer is not set to python-mode automatically (it is in fundamental mode). How can I get it so that the buffer opens with the correct language mode?

Answer 1

I don't know Rudel well enough to give a 100% solution, but what you want to do is something like this:

(add-hook 'rudel-document-attach-hook 'my-rudel-set-mode-appropriately)
(defun my-rudel-set-mode-appropriately (document buffer)
  "try to set the mode appropriately"
  (set-buffer buffer)
  (let ((buffer-file-name ...get-name-from-document...))
    (set-auto-mode)))

Only, you need to replace the ...get-name-from-document... portion of the code with something that evaluates to the file name that you want, for example, if the buffer is named myfile.py, then you can change that to (buffer-name). But, if the buffers get odd names, perhaps you need to extract the name from the document object (Rudel internally uses a document object to represent the thing you are sharing). So, if (buffer-name) doesn't work, you can try (rudel-suggested-buffer-name document).

i.e. try the above code but using one of these lines:

  (let ((buffer-file-name (buffer-name)))

and

  (let ((buffer-file-name (rudel-suggested-buffer-name document)))

The set-auto-mode will use value of buffer-file-name to determine the major mode using the general Emacs mechanisms.

Answer 2

I know absolutely nothing about how rudel works. However, have you tried explicitly setting the mode in the text file? Try adding something like this to the first line of the file:

# -*- mode: python; fill-column: 75; comment-column: 50; -*-

Putting a line like this first in the file will cause emacs to ignore the file's extension and open in the given mode.