Tell ido to ignore all star buffers except for some

Question

Normally I want ido to ignore all non-user buffers, i.e. all buffers which start with a *. I have achieved this using the following setting:

(setq ido-ignore-buffers '("\\` " "^\*"))

However, this poses a problem when working with a shell or an interpreter, e.g. ielm, where the interaction buffer is named *ielm*. Obviously adding all buffers to be ignored manually is not really an option because the list can get quite long with a lot of different emacs packages loaded. I know about C-a which disabled the ignore pattern from within ido, however, I don't want to hit C-a every time I switch to an ielm buffer.

My question is:

Is there some variable which allows to specify buffers which ido should not ignore (although they match the normal ignore list)? Or is there some other approach for solving this?

Answer 1

The list that the ido-ignore-buffers variable points to may contain not only regular expressions but also functions (any mix of them, actually). It's easy to provide a function to filter out all non-user buffers except *ielm*:

(defun ido-ignore-non-user-except-ielm (name)
  "Ignore all non-user (a.k.a. *starred*) buffers except *ielm*."
  (and (string-match "^\*" name)
       (not (string= name "*ielm*"))))

(setq ido-ignore-buffers '("\\` " ido-ignore-non-user-except-ielm))

Here's an example of having multiple unignored buffer names:

(setq my-unignored-buffers '("*ielm*" "*scratch*" "*foo*" "*bar*"))

(defun my-ido-ignore-func (name)
  "Ignore all non-user (a.k.a. *starred*) buffers except those listed in `my-unignored-buffers'."
  (and (string-match "^\*" name)
       (not (member name my-unignored-buffers))))

(setq ido-ignore-buffers '("\\` " my-ido-ignore-func))

An interesting example of using ignore functions can be found among comments in the ido.el source code (I've removed ;; at the beginning of each line):

(defun ido-ignore-c-mode (name)
  "Ignore all c mode buffers -- example function for ido."
  (with-current-buffer name
    (derived-mode-p 'c-mode)))

Basically, once you've got buffer name, you can do any checking/ignoring you want.