How to make desktop-save store relative paths?

Question

Perhaps I'm kind of misusing that feature – but I find desktop files rather handy to be kept with projects. Clearly, it doesn't make much sense then to store absolute paths for the files to be opened; rather, I would like paths relative to the desktop file's own folder, so I can move the entire project folder al gusto and always load the desktop file within.

Emacs has indeed no problem opening such “local desktop files”, like

(desktop-create-buffer 206
  "src/Main.hs"
  "Main"
  'haskell-mode
  ... )

However, as soon as I do desktop-save (e.g. because I added a new file to the project), all the stored paths will get changed to absolute format

(desktop-create-buffer 206
  "/home/me/right/now/the/project/is/stored/here/src/Main.hs"
  "Main"
  'haskell-mode
  ... )

It's not hard to undo this by hand or with a quick sed command, but that's quite annoying. Can I tell emacs not to store those paths in absolute format?

Answer 1

I believe you can achieve this by setting desktop-file-name-format to "local".

Here's what describe-variable says about it:

desktop-file-name-format is a variable defined in `desktop.el'.
Its value is absolute

Documentation:
Format in which desktop file names should be saved.
Possible values are:
   absolute -- Absolute file name.
   tilde    -- Relative to ~.
   local    -- Relative to directory of desktop file.

You can customize this variable.

This variable was introduced, or its default value was changed, in
version 22.1 of Emacs.

With the "local" desktop-file-name-format you just need to make sure that the desktop file is saved in the top directory of a project. One way to do this is by setting desktop-dirname using Per-Directory Local Variables.